Abstracts of LT23

Session 22CP Session 22CP

Pressure effect on the resistivity of the filled skutterudite compounds

Masato Hedo^a, Yoshiya Uwatoko^a, Hitoshi Sugawara^b, Tatsuma D. Matsuda^c, Hideyuki Sato^b

^aISS, University of Tokyo, Kashiwanoha 1-5-1, Kashiwa-shi, Chiba 277-8581, Japan.

^bTokyo metropolitan University, Minami-Osawa 1-1, Tokyo 192-0397, Japan.

^cAdvanced Science Research Center, JAERI, Tokai, Ibaraki 319-1195, Japan.

Ternary intermetallic compounds RT₄X₁₂ with the filled skutterudite structure have attracted much attention, since the large number of novel phenomena have been discovered in these compounds. Among them, PrFe₄P₁₂ have received special attentions because of their quite uncommon properties,such as the anomalous heavy electron state with quadrupole ordering at low temperature. CeOs₄Sb₁₂ shows semiconducting behavior with a very small energy gap. These unique properties might be attributed to the large c-f hybridization strength, which originated in the unique structure. In order to clarify the electronic structure in these compounds, we have measured the transport properties under high pressure.

22CP3 paper-pdf

Low temperature properties of Sm-based filled skutterudite phosphides

R. Giri^a, Y. Shimaya^a, K. Kihou^a, C. Sekine^a, I. Shirotani^a, K. Matsuhira^b, T. Yagi^c

^aDepartment of Electrical and Electronic Engineering, Muroran Institute of Technology, 27-1 Mizumoto cho, Muroran 050-8585 Japan

^bKyushu Institute of Technology, Kitakyushu 804-8550 Japan

^cISSP,University of Tokyo, Kashiwa 277-8581 Japan

Filled skutterudite compounds SmTP(T=Fe,Ru,Os) have been prepared at high temperature and high pressure. The low temperature properties of these materials have been studied by means of electrical resistivity, magnetic susceptibility and specific heat measurements. SmFeP and SmOsP behave as a metalic below room temperature. On the other hand, SmRuP shows metal-insulater transition near 16K. SmOsP shows an antiferromagnetic ordering at 5K and transition temperature shifts to lower temperature, while applying high magnetic field. SmFeP is paramagnetic down to 2K.

22CP4 paper-pdf

Ferromagnetic Heavy Fermion System SmFe₄P₁₂

Naoya Takeda, Masayasu Ishikawa

Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan

We present the magnetic properties of a filled skutterudite compound SmFe₄P₁₂. The magnetic susceptibility and specific heat measurements reveal a ferromagnetic phase transition at 1.5 K. The temperature dependence of the electrical resistivity exhibits a Kondo effect and the electronic specific heat coefficient atains as large as 370 mJ/mole· K². This compound is the first Sm-based heavy fermion system with a ferromagnetic ground state.

22CP5 paper-pdf

Anisotropy of the heavy fermion state in PrFe₄P₁₂

T. Namiki, Y. Aoki, E. Kuramochi, T. D. Matsuda, H. Sugawara, H. Sato

Dept. of Physics, Tokyo Metropolitan University, Hachioji-shi, Tokyo 192-0397, Japan

Recently it has been confirmed that PrFe₄P₁₂ has a rare 4f²-based heavy fermion (HF) state in high fields where a non-magnetic ordered state is suppressed. We have studied the anisotropy of the HF state by applying magnetic fields (H) along different crystalline directions. For H//á100 ñ and H//á110 ñ, the electronic part of specific heat (C_el/T) shows Fermi-liquid like behaviors at low temperatures, while C_el/T shows a lnT-like divergence below 2 K for H//á111 ñ. Correspondingly, electrical resistivity r(T) shows an almost linear-in-T behavior below 1 K for H//á111 ñ, while T² dependence is dominating for the other two directions. A fact that the observed non-Fermi-liquid (NFL) behaviors for H//á111 ñ are insensitive to the magnetic field may reflect the NFL nature of the ground state that is concealed by the non-magnetic ordered state in low fields.

22CP6 paper-pdf

FLAPW Electronic Band Structure of the Filled Skutterudite ThFe₄P₁₂

Katsuhiko Takegahara^a, Hisatomo Harima^b

^a Dept. of Materials Science and Technology, Hirosaki University, Hirosaki, Aomori 036-8561, Japan

^b The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan

The LaFe₄P₁₂ compound has been known to be the metal with one hole per formula unit. Thus the ThFe₄P₁₂ compound is expected to be semiconducting, since thorium ion is believed to be tetravalent. However, the electric resistivity and infrared reflectance spectroscopy measurements have suggested that the ThFe₄P₁₂ compound behaves like metal.¹

The electronic band structure is calculated for ThFe₄P₁₂ by using an FLAPW method. The result reveals that, between the filled valence bands and empty conduction bands, there is a direct band gap at the G point with gap width of 0.0331 Ry (0.45 eV), contrary to experimental results.

22CP7 paper-pdf

Resonant X-ray Scattering Study on the filled skutterudite PrFe₄P₁₂

K. Ishii^a, L. Hao^b, T. Inami^a, Y. Murakami^a,^d, K. Iwasa^b, M. Kohgi^b, Y. Aoki^b, H. Sugawara^b, H. Sato^b, S. Imada^c, H. Nakao^d, H. Sawa^e, Y. Wakabayashi^e

^aSynchrotron Radiation Res. Ctr., Japan Atomic Energy Research Institute, Hyogo 679-5148, JAPAN

^bDepartment of Physics, Tokyo Metropolitan University, Tokyo 192-0397, JAPAN

^cDepartment of Material Physics, Osaka University, Osaka 650-8531, JAPAN

^dDepartment of Physics, Tohoku University, Sendai 980-8578, JAPAN

^ePhoton Factory, Institute of Materials Structure Science, Tsukuba 305-0801, JAPAN

One of the filled skutterudites, PrFe₄P₁₂, attracts interest because of a non-magnetic ordered ground state and a heavy fermion state under high magnetic field. Theoretically, antiquadrupolar ordering is proposed as the ordered state. We have performed resonant x-ray scattering study at the Pr-L_III absorption edge, and found that two Pr ions in a body-centered cubic unit cell certainly have a different electronic state.

22CP8 paper-pdf

⁵⁷Fe Mössbauer spectroscopic Study of PrFe₄P₁₂

Satoshi Tsutsui^a, Kaori Kuzushita^b, Takashi Tazaki^b, Shotaro Morimoto^b, Saburo Nasu^b, Tatsuma D. Matsuda^c, Hitoshi Sugawara^d, Hideyuki Sato^d

^aJapan Synchrotron Radiation Research Institute, Mikazuki, Hyogo 679-5198, Japan

^bGraduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan

^cAdvanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan

^dGraduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan

PrFe₄P₁₂ has recently been the most interesting compounds in the filled-skutterddite compounds. This compound shows the phase transition at 6.5 K. The ⁵⁷Fe Mössbauer parameters obtained in the present work show no temperature dependence around this temperature. We have also performed the ⁵⁷Fe Mössbauer spectroscopy under the applied magnetic field.

22CP9 paper-pdf

Elastic properties of Re-Ru₄Sb₁₂ (Re; La, Pr)

Tomoyuki Kumagai^a, Yoshiki Nakanishi^a, Masahito Yoshizawa^a, Hitoshi Sugawara^b, Hideyuki sato^b

^aDepartment of Materials Science and Engineering, Iwate University, Morioka 020-8551, Japan

^bDepartment of Physis, Tokyo Metropolitan University, Hachioji 192-0397, Japan

We have studied elastic properties of Re-Ru₄Sb₁₂ (Re; La, Pr) by means of ultrasonic measurement. They both exhibit a superconducting transition at temperature of T_c = 3.2 K for LaRu₄Sb₁₂ and T_c = 1.0 K for PrRu₄Sb₁₂. No distinct anomaly was observed at T_c in the both compounds. Elastic softening towards low temperature, which is reflected a 4f ground state of Pr ion doesn't appear. It suggests the 4f ground state to be G₁ singlet in PrRu₄Sb₁₂.

22CP10 paper-pdf

Structural Phase Transition in Trivalent Skutterudites

S. H. Curnoe^a, K. Ueda^b, H. Harima^c, K. Takegahara^d

^aDepartment of Physics and Physical Oceanography, Memorial University of Newfoundland, Canada

^bInstitute for Solid State Physics, University of Tokyo, Kashiwa, Japan

^cInstitute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan

^dDepartment of Materials Science and Technology, Hirosaki University, Hirosaki, Aomori 036-8561, Japan

The trivalent skutterudites PrRu₄P₁₂, PrFe₄P₁₂, NdFe₄P₁₂, SmRu₄P₁₂, GdRu₄P₁₂ and TbRu₄P₁₂ display resistivity upturns, attributable to a partial (or full) metal-insulator transition, and magnetisation anomalies indicative of an ordered ground state. The common feature of these materials may be nesting of the Fermi surface, which is unstable due to coupling between local f-electrons and lattice distortions. We examine symmetry allowed couplings in order to determine which types of distortions may lead to a structural phase transition, and the possible 4f-electron ground states with which they are compatible.

22CP11 paper-pdf

NMR study of magnetic properties in SmRu₄P₁₂

K. Fujiwara^a, K. Ishihara^b, K. Miyoshi^a, J. Takeuchi^a, C. Sekine^c, I. Shirotani^c

^aDepartment of Materials Science, Shimane University, Matsue 690-8504, Japan

^bMterials Research Laboratory, FURUKAWA CO. LTD., Tsukuba 305-0856, Japan

^cMuroran Institute of Technorogy, 27-1, Mizumoto, Muroran 050-8585, Japan

³¹P-NMR spectra and nuclear spin-lattice relaxation time T₁ have been measured in the temperature range between 1.3 and 300 K. NMR spectrum becomes suddenly broad below metal-insulator transition temperature (T_M-I=16.5K), suggesting that SmRu₄P₁₂ shows magnetic phase transition just below T_M-I. Broadening of the NMR line indicates that the amplitude and direction of internal field distribute randomly at P sites , that is, antiferromagnetic order is complicated, such as SDW or incommensurate one. Relaxation rate 1/T₁ obeys exponential relation (exp[-DE/k_BT]) below T_M-I. This seems to be because a gap is open in the spin excitation spectrum.

22CP12 paper-pdf

Magnetic Field Effects on the Pressure-Induced Colossal Maximum in Electrical Resistivity of CeSb

Okayama Yasushi^a, Suzuki Takashi^b, Môri Nobuo^b

^aDepartment of physics, Saga University, Saga 840-8502, Japan

^bInstitute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 227-8581, Japan

Pressure-induced sharp maximum in electrical resistivity r(T) is observed near 35K at pressures above 1.5GPa. The peak value increases rapidly in proportion to the square of pressure up to 6GPa, and at 7GPa it reaches a vaule nearly 23 times as large as that at ambient pressure. We have measured r(T) curves of CeSb at 4GPa under high magnetic fields up to 16T. The peak value of this colossal maximum exhibits a very rapid decrease with increasing magnetic field and disappears completely above 6T. This result strongly suggests that the cause of the colossal maximum is attribute to some magnetic origin.

22CP13 paper-pdf

Antiferromagnetism and magnetoleasticity of UNiAl

V. Sechovský^a, F. Honda^a, P. Svoboda^a, M. Doerr^b, M. Rotter^b, M. Loewenhaupt^b

^aDept. of Electronic Structures, Charles University, 121 16 Praha 2, The Czech Republic

^bInstitut für Angewandte Physics, TU-Dresden, 01062 Dresden, Germany

Results of thermal-expansion (TE) and magnetostriction (MS) measurements will be presented for the antiferromagnet UNiAl (T_N = 19.3 K), which undergoes at T < 7 K metamagnetic transition (MT) with a critical field B_C = 11.4 T (applied along the c-axis of hexagonal structure). The anomalous TE contributions observed at T up to 3T_N can be removed by magnetic fields sufficiently high ( > 16 T) to suppress the AF correlations (or short range AF order), which are believed to be responsible for TE anomalies in paramagnetic state. The MT at T < 7 K is accompanied by an abrupt MS step of the order of 10-4; negative (positive) along the c-axis (a-axis) leaving the volume effect negligible.

22CP14 paper-pdf

Specific Heat of CeMg₂Cu₉ with a Two-dimensional Ce Arrangement

Masakazu Ito^a, Koji Asada^a, Yuko Nakamori^b, Hironobu Fujii^b, Toshizo Fujita^a, Takashi Suzuki^a

^aDepartment of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima 739-8530

^bFaculty of Integrated Arts & Science, Hiroshima University, Higashi-Hiroshima 739-8526

We have carried out the specific heat measurements under pressures between 0 and 0.91 GPa on CeMg₂Cu₉, in which the Ce atoms are a two-dimensional arrangement. A large peak is observed at T_N = 2.5 K for 0 GPa. The position of T_N increases below 0.89 GPa, and changes into decrease with pressurization. The released magnetic entropy S_m below T_N is about 60% of that expected for the twofold spin degeneracy. This suggests the Kondo-compensated moments are formed in the low temperature range. These behaviors are similar to the pressure-induced superconductor CeRhIn₅ with a two-dimensional arrangement of Ce atoms.

22CP15 paper-pdf

Insulator-metal transition studied by heat capacity measurements on SmS

Kazuyuki Matsubayashi, Hitoshi Mukai, Takashi Tsuzuki, Takashi Nishioka, Noriaki K. Sato

Department of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan

We have measured the specific heat of SmS at pressures up to ~ 7.5 kbar. We observed that the electronic specific heat coefficient g shows a steep increase at around P_c ~ 3.5 kbar, which corresponds to an insulator-metal phase transition. In the metal phase above P_c, we found that g exceeds 100 mJ/mole K², indicating a strongly correlated metallic state. On the other hand, we observed an anomaly in the temperature dependence of the specific heat around 1 K; a sample exhibits a huge g-value that amounts to ~ 200 mJ/mole K². We will discuss this origin of the anomaly.

22CP16 paper-pdf

Magnetic properties of URhSi single crystal

Fuminori Honda^a, Sechovský Vladimir^a, Andreev V. Alexander^a, Prokes Karel^b

^aJoint Lab. for Magnetic Studies, Ke Karlovu 5, 121 16 Prague 2, Czech Republic

^bHahn-Meitner-Institute, SF-2, D-141 09 Berlin, Germany

URhSi which crystallizes in the orthorhombic TiNiSi-type structure, is an itinerant 5f- electron ferromagnet having T_c = 9.5 K with tiny magnetic moment of uranium. Due to the existence of strong magnetocrystalline anisotropy in this compound, single crystalline studies are desired. In the present work, we have grown URhSi single crystal and carried on magnetization, M(B), measurement at 2 K and magnetic field up to 9 T. It is found that the M(B) of URhSi is highly anisotropic and easy-magnetization direction is the c-axis. M(B) curves along a- and b- axis are similar and non-zero spontaneous moment are observed for all axes. Specific heat result will also be presented.

22CP18 paper-pdf

Magnetic Properties of CeRu₂Si₂ at Ultra Low Temperatures

D. Takahashi^a, S. Abe^a, H. Mizuno^a, T. Ogawa^a, K. Hayashi^a, K. Matsumoto^a, H. Suzuki^a, Y. ¯Onuki^b

^aDepartment of Physics, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan

^bGraduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan

We simultaneously measured the ac susceptibility and dc magnetization of the heavy fermion compound CeRu₂Si₂ in various small magnetic fields at temperatures down to 170mK. The susceptibility and magnetization increased below 100mK followed by Curie law with small magnetic moment 0.02m_B/Ce. In fields higher than 0.20mT, the susceptibility showed the peak, the temperature (T_M) and height of which were higher and lower with increasing the field, respectively. In addition, approaching T_M, increase in the static magnetization became flat and showed a plateau in fields higher than 0.39mT. These results reflect the spin fluctuation of the itinerant 4f electron with the antiferromagnetic correlations.

22CP19

Bound states in the one-dimensional Kondo lattice model

Simon Trebst^a, Hartmut Monien^a, Manfred Sigrist^b

^aPhysikalisches Institut der Universität Bonn, Germany

^bTheoretische Physik, ETH, 8093 Zürich, Switzerland

We apply recently developed high-order coupling expansion techniques to study zero-temperature properties of 2-hole excitations in the one-dimensional Kondo lattice model around half-filling. Starting from the insulating Kondo spin liquid phase which is the strong-coupling limit of isolated dimers we expand effective Hamiltonians in the subspaces of single-hole and two-hole excitations. This way we can expand the dispersion of a single hole excitation up to 10th order. With growing hopping amplitudes the effective mass of the holes is found to strongly increase. In the two-hole sector we find a continuum of scattering states and two distinct states which separate from the continuum around k=p momentum. These 2-hole states can be identified as singlet and triplet combination of two hole excitations.

22CP20 paper-pdf

M⁴ Scaling of Negative Magnetoresistance in CeSi

Satoru Noguchi

Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan

CeSi crystallizes in the orthorhombic FeB type structure. Below 6 K it has a sinusoidally modulated magnetic structure, which is incommensurate with the crystal lattice. Magnetization for H||b shows a metamagnetic transition at 0.5 T and saturates with the moment of 1.7m_B/Ce. In the compound, a large negative magnetoresistance for H||b was observed. It was found that the scaling between the magnetoresistance and the magnetization shows an interesting relation of Dr/r₀ µ -(M/M_s)⁴ in a wide field region up to 8 T. This may suggest that in the system an interatomic coupling of fluctuation is dominant as well as a single-site fluctuation with relation to the unique magnetic structure.

22CP21

Specific Heat and Electrical Resistivity Measurements in Pr_0.03La_0.97Pb₃

Tatsuya Kawae^a, Tatsuharu Yamamoto^a, Kenji Yurue^a, Masaki Mito^a, Kazuyoshi Takeda^a, Tetsuo Kitai^b

^aDepartment of Applied Quantum Physics, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan

^bFaculty of Engineering, Kyushu Institute of Technology, Kitakyushu 804-8585, Japan

We have measured specific heat C and electrical resistivity r for Pr_0.03La_0.97Pb₃ with the G₃ doublet in the crystalline-electric-field ground state to examine the Kondo effect arising from the correlation between the quadrupolar moments and the conduction electrons. It is found that C/T increases monotonically with lowering temperature below 1.5 K, which is clearly different from that in the Pr concentrated region. Moreover, r shows the clear drop below 3 K. The possible origin of these results is discussed.

22CP22 paper-pdf

Magnetic Susceptibility of LaRu₃Si₂

Yutaka Kishimoto^a, Takashi Ohno^a, Takehiko Hihara^b, Kenji Sumiyama^b, Goutam Ghosh^c, Laxmi C. Gupta^c

^aFaculty of Engineering, Tokushima University, Tokushima 770-8506, Japan

^bNagoya Institute of Technology, Nagoya 466-8555, Japan

^cTata Institute for Fundamental Research, Bombay 400 005, India

To study the mixed valence behavior in RRu₃Si₂ (R=rare earth elements), the magnetization M of LaRu₃Si₂ was measured in the normal state. The magnetization curve ( M-H curve ) was analyzed with assuming that it consists of an intrinsic paramagnetic part and a ferromagnetic impurity part. The obtained magnetic susceptibility is very dependent on temperature, which is considered to be due to a high density of states and narrow band. This result is also considered to be related to its considerably high superconducting transition temperature T_s=7 K.

22CP23 paper-pdf

A Simple Tight-Binding Model Description of the Conduction Band of the Kondo Insulator YbB₁₂

Tetsuro Saso

Department of Physics, Faculty of Sciences, Saitama University, Shimo-Ohkubo 255, Saitama-City, 338-8570 Japan.

It is shown that the conduction band of typical Kondo insulator YbB₁₂ can be expressed rather well by a simple tight-binding model of 5d_e-orbitals on Yb. The (dds) overlapping integral is considered to include the effect of B₁₂. Mixing of f-states with the conduction band can be described in terms of the extended Slater-Koster integrals with the spin-orbit interactions. Using this model, thermal, thermoelectric, transport and magnetic properties of YbB₁₂ will be discussed. Effect of strong correlation on the thermal current will be also discussed

22CP24 paper-pdf

Magnetism of UCo_1-xT_xAl (T = Fe, Ni) single crystals

A.V. Andreev^a, V. Sechovský^a, N. V. Mushnikov^b, T. Goto^b

^aJoint Lab. for Magnetic Studies, Ke Karlovu 5, 121 16 Prague 2, Czech Republic

^bISSP, Tokyo Univ. Kashiwanoha 5-1-5, Kashiwa-shi, Chiba-ken 277-8581 Japan

The specific metamagnetic (M) behavior of UCoAl is easily modified to ferromagnetism (F) or conventional paramagnetism with doping UCoAl by suitable elements. We demonstrate these features in the magnetization study of single crystals of the UCo_1-xT_xAl (T = Fe, Ni) at 1.5-40 K. The Ni substitution for Co yields an increase of the critical field and a gradual suppression of M, which disappears at x=0.10. The compounds UCo_0.95Fe_0.05Al and UFe_0.50Ni_0.50Al are F below 30 K and 52 K, respectively. For UCo_0.95Fe_0.05Ni_0.05Al and UCo_0.98Fe_0.02Al, which also exhibit F, traces of M are indicated on magnetization curves. The doping-induced F is very sensitive to external pressure. Hydrostatic pressure of only 0.3 GPa is sufficient to suppress all signs of F and restore M in UCo_0.98Fe_0.02Al.

22CP25 paper-pdf

Evolution of magnetic structures in U(Ni_1-xPd_x)₂Si₂ system

P. Svoboda^a, A.V. Andreev^b, F. Honda^a, J. Vejpravová^a, K. Prokes^c, V. Sechovský^a

^aCharles Univ., Dept. of Electronic Structures, 121 16 Prague 2, The Czech Rep.

^bInst. of Physics, Acad. of Sciences, 182 21 Prague 8, The Czech Rep.

^cBENSC, HMI - Berlin, D 14109 Berlin, Germany

The influence of Pd-Ni substitution on the formation of magnetic phases in the tetragonal U(Ni_1-xPd_x)₂Si₂ system and the corresponding magnetic phase diagrams are presented. The single crystals of two different substitutions x = 0.15 and 0.10 were grown and detailed studies by neutron diffraction were performed in horizontal magnetic fields up to B = 6 T. Both compounds order antiferromagnetically (AF) and exhibit three different AF structures below the Neel temperature. All three structures are formed by ferromagnetic basal planes stacked along c-axis with different q = (0, 0, q_z) propagation. For x = 0.10, the co-existence of two magnetic phases in the ground-state was observed.

22CP26 paper-pdf

Thermodynamic properties of SmCu₂

Jana Vejpravová^a, Pavel Svoboda^b, Martin Rotter^b, Mathias Doerr^b, Michael Loewenhaupt^b

^aCharles Univ., Dept. of El. Structures, 121 16 Prague 2, Czech Republic

^bTU Dresden, IAPD, D-01069 Dresden, Germany

Intermetallic compound SmCu₂ crystallizes in the CeCu₂-type structure (space group Imma) and orders antiferromagnetically (AF) below the N\' eel temperature T_N = 23 K. A single crystal of SmCu₂ was grown and the temperature dependence of specific heat was measured in the low-temperature region to determine the magnetic phase transitions. Four sharp anomalies were detected at temperatures T = 22.3, 17.7, 16.4 and 3.7 K, which were attributed to T_N and three additional order-to-order magnetic phase transitions between three AF phases. The detailed analysis of specific heat in the low-temperature region was performed by comparing the specific heat of SmCu₂ and that of non-magnetic analogues LuCu₂ and YCu₂. The thermodynamic properties of SmCu₂ in ordered state are presented here.

22CP27 paper-pdf

Low temperature specific heat enhancement in Fe₂VGa

C. S. Lue^a, H. D. Yang^b, Y. -K. Kuo^c

^aDepartment of Applied Physics, National Chiayi University, Chiayi 600, Taiwan

^bDepartment of Physics, National Sun-Yat-Sen University, Kaohsiung 804, Taiwan

^cDepartment of Physics, National Dong Hwa University, Hualien 974, Taiwan

Low-temperature specific heat measurements on the Heusler-type compounds Fe₂VGa have been performed. We observed the sample-dependent upturn in C/T at low temperature which is attributed to the effect of magnetic impurities and/or clusters. After subtracting this extrinsic effect, the resulting g still indicated heavy fermion behavior with an effective mass of about 50 times larger than the value extracted from NMR results. Possible mechanisms for such an enhancement will be discussed and compared to those in other Heusler alloys.

22CP28 paper-pdf

Magnetic Behavior in Nonmagnetic Atom Disorder System Ce₂CuSi₃

D. X. Li^a, Y. Shiokawa^a, S. Nimori^b, Y. Haga^c, E. Yamamoto^c, T. D. Matsuda^c, Y. Onuki^c

^aInstitute for Materials Research, Tohoku University, Oarai, Ibaraki, 311-1313 Japan

^bNational Institute for Materials Science, 3-13 Sakura, Tsukuba, 305-0003 Japan

^cAdvanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki, Japan

Nonmagnetic atom disorder system Ce₂CuSi₃ is found to show the spin-glass behaviors below T_f=2.7 K, e.g. the frequency-dependent ac susceptibility, the irreversibility of the dc magnetization and the long-time magnetic relaxation effect etc. On the other hand, the appearances of a broad peak in specific heat curve and the evident decrease of electrical resistivity around T=3.5 K seem to suggest the formation of magnetically ordered state or the extended magnetic clusters in this compound. The complex magnetic behaviors are considered to originate from the competition between ferro- and antiferromagnetic exchange interactions and discussed comparing with other isostructural 2:1:3 compounds.

22CP29 paper-pdf

Crossover between "localized" and ïtinerant" antiferromagnetic states in Ce(Ru_0.9Rh_0.1)₂(Si_1-yGe_y)₂ driven by chemical pressure

Yoshikazu Tabata, Kenji Watanabe, Toshifumi Taniguchi, Chikahide Kanadani, Shuzo Kawarazaki

Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan

We have investigated the magnetization process of the pseudobinary Kondo-lattice system Ce(Ru_0.9Rh_0.1)₂(Si_1-yGe_y)₂. The base material Ce(Ru_0.9Rh_0.1)₂Si₂, which has a spin density wave(SDW) phase below T_N = 5.0 K, shows two-step metamagnetic behavior at H_c and H_m; the SDW-Fermi liquid(FL) transition occurs at H_c, and FL state becomes unstable and localized spin character recovers at H_m. By substituting Ge for Si, H_m reduces very rapidly and disappears for y > 0.08, where the magnetization curve is quite similar to those of localized Ising spin antiferromagnets(AF). This observation is interpreted as a manifestation of crossover of the character of the AF state from ïtinerant" to "localized" induced by the negative chemical pressure.

22CP30

Heat capacity of SmB₆ at low temperatures

S. Gabáni^a, K. Flachbart^a, E. Konovalova^b, M. Orendác^c, Y. Paderno^b, V. Pavlík^a, J. Sebek^d

^aInstitute of Experimental Physics, Slovak Acad. Sci., SK-04353 Kosice, Slovakia

^bInstitute for Problems of Material Sciences, National Acad. Sci. Ukraine, UA-252142 Kiev, Ukraine

^cDepartment of Experimental Physics, P.J. Safárik University, SK-04154 Kosice, Slovakia

^dInstitute of Physics, Acad. Sci. Czech Republik, CZ-18221 Prague, Czech Republik

We have investigated the low temperature properties of the narrow-gap semiconductor SmB₆ by means of heat capacity measurements at temperatures between 0.1 and 20 K and in magnetic field up to 9 T. The heat capacity measurements show a metallic-like behaviour of this material at low temperatures and reveal, moreover, an enhancement of the specific heat below about 2 K, which can be attributed to the formation of a coherent state. The influence of magnetic field on the formation of this state is discussed.

22CP31

Study of the magnetic properties of Ce₃Pd₂₀Si₆ and Ce₃Pd₂₀Ge₆ compounds

V. N. Duginov^a, A. V. Gribanov^b, K. I. Gritsaj^a, V. N. Nikiforov^b, V. Yu. Pomjakushin^a, A. N. Ponomarev^c, Yu. D. Seropegin^b

^aJoint Institute for Nuclear Research, Dubna 141980, Russia

^bMoscow State University, Moscow 119899, Russia

^cRSC "Kurchatov Institute", Moscow 123182, Russia

The compounds Ce₃Pd₂₀Ge(Si)₆ manifest the unusual physical properties which categorize them as a magnetic Kondo systems. The features of the magnetic behaviour of these compounds can be explained by the existence of two relatively separated Ce-subsystems.

We studied the magnetic properties of the polycrystalline samples of Ce₃Pd₂₀Ge(Si)₆ by the muonic technique (mSR method).

The details of the magnetic behaviour of Ce₃Pd₂₀Ge(Si)₆ at the temperatures below 1 K are presented.

22CP32 paper-pdf

Itinerant Antiferromagnetism of Mn₃Si and CuMnSb

C. Pfleiderer^a, J. Buf^a, A. Faißt^a, H. von Löhneysen^a,^b

^aPhysikalisches Institut, Universität Karlsruhe, Wolfgang-Gaede Str. 1, D-76137 Karlsruhe, Germany

^bForschungszentrum Karlsruhe, Institut für Festkörperphysik, D-76021 Karlsruhe, Germany

We report an experimental study of the specific heat, resistivity and magnetisation of the antiferromagnetically ordered metals Mn₃Si and CuMnSb at low temperatures and high magnetic fields. The bulk properties and the low values of T_N of these compounds are essentially unchanged up to 14 T. This suggests a stability of the antiferromagnetic order to high magnetic field that is incompatible with present day models for magnetism in metals, in particular the standard model of itinerant magnetism. In turn our observations question the validity of Fermi liquid theory in its present form free of a theoretical agenda, e.g., the vicinity to a magnetic quantum phase transition or perfect nesting of the band-structure.

22CP33

Magnetic properties of Ce(Rh_1-xRu_x)₂Si₂ single crystals for x up to 0.35

P. Haen^a, F. Lapierre^a, P. Lejay^a, C. Sekine^b, H. Bioud^c

^aCRTBT, laboratoire associé à l'Université Joseph Fourier, CNRS, BP 166, 38042 Grenoble cedex, France

^bDept. of Electr. Eng., Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran 050-8585, Japan

^cFac. des Sciences, Dépt. de Physique, Université Chouaib Doukkali, BP 20, El Jadida, Morroco

We report magnetic, volumic and transport properties of Ce(Rh_1-xRu_x)₂Si₂ single crystals. The antiferromagnetic (AF) transition occuring at T_N₁ = 36 K for x = 0 decreases rapidly on increasing x and vanishes for x = 0.35. This variation scales with an increase of the Kondo temperature. A second AF transition occuring at T_N₂ = 27 K for x = 0, has disappeared for x as small as 0.01. The anomalies at T_N₁ are smoothed for x ³ 0.05. However, the simultaneous large increase of residual resistivity is not only due to disorder, as shown by its 40 to 50 percent decrease in a magnetic field of 22 T. These results will be compared with the properties of non-ordered alloys (0.35 £ x £ 0.6) and discussed.

22CP34 paper-pdf

Contrastive transport properties in Y₇Rh₃ and La₇Rh₃

Yuko Nakamori^a, Takanori Tsutaoka^b, Toshihiko Tokunaga^b, Masakazu Ito^c, Takashi Suzuki^c, Toshizo Fujita^c, Hironobu Fujii^a

^aFaculty of Integrated Arts and Science, Hiroshima University, 739-8521 Hiroshima, Japan

^bFaculty of Education, Hiroshima University, 739-8524 Hiroshima, Japan

^cGraduate School of advanced Sciences of matter, 739-8526 Hiroshima, Japan

We have reported that light/heavy-rare-earth R₇Rh₃ compounds show ferromagnetic/antiferromagnetic behavior and metallic/semimetallic transport properties. To clarify the origin of contrastive properties in isostructural R₇Rh₃, we studied non-magnetic compound Y₇Rh₃ and La₇Rh₃, in which lattice constants are almost the same as in heavy- and light-rare-earth compounds respectively. The results of Hall effect indicated that the number of carrier for Y₇Rh₃ (0.04/atom) is smaller than that for La₇Rh₃ (0.29/atom). It was clarified from magnetic studies that Y₇Rh₃ is nearly localized 4d electron system.

22CP35

Magnetoresistance of URh₃B_0.7 Single Crystal

Y. Homma^a, T. Yoshida^b, Y. Shiokawa^a

^aInstitute for Materials Research, Tohoku University, Oarai Ibaraki-ken 311-1313, Japan

^bInstitute for Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577, Japan

Boron addition is a powerful technique for controlling of magnetism in the uranium compounds, such as URh₃B_x. We studied the magnetic and transport properties in the URh₃B_0.7 single crystal prepared by Czochralski method using a tetra-arc furnace. This crystal did not show magnetic order down to 1.8 K, just as reported data of the polycrystalline URh₃B_0.7. But large negative enhancement was observed in the transverse magnetoresistance of [100] axis at H ³ 5.5 T.

22CP36 paper-pdf

Neutron Diffraction Study of Itinerant Antiferromagnet UPtGa₅ and UNiGa₅

Koji Kaneko^a, Naoto Metoki^a, Yoshinobu Ishii^a, Yoshihumi Tokiwa^a,^b, Yoshinori Haga^a, Yoshichika ¯Onuki^a,^b

^aAdvanced Science Research Center, Japan Atomic Energy Institute, Tokai, Ibaraki 319-1195, Japan

^bGraduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan

UNiGa₅ and UPtGa₅ which is isostructural to the heavy fermion superconductors CeRhIn₅ and PuCoGa₅ undergo an antiferromagnetic order transition at 86 K and 26 K, respectively. It should be pointed out that the coupling of magnetic moments of uranium within the (0 0 1) plane is different in these compounds: ferromagnetic coupling in UPtGa₅ and antiferromagnetic one in UNiGa₅, while the coupling along the [0 0 1] is antiferromagnetic in both compounds. We observed a large changes of z parameter of Ga 4i site in UNiGa₅ around the antiferromagnetic order transition. This strain indicates that spin and orbital degree of freedom play an significant role in the different magnetic structures between these compounds.

22CP37 paper-pdf

High field magnetostriction of CeRh₂Si₂

Osamu Naito^a, Tetsuya Takeuchi^b, Koichi Kindo^a, Yoshikazu Tabata^c, Syuzo Kawarazaki^c

^aKYOKUGEN, Osaka University, Toyonaka, Osaka 560-8531, Japan

^bLow Temperature Center, Osaka University, Toyonaka, Osaka 560-0043, Japan

^cDepartment of Earth and Space Science, Osaka University, Toyonaka, Osaka 560-0043, Japan

Magnetostriction on a single crystal CeRh₂Si₂ was measured by using strain gauge in pulsed magnetic fields up to 50 T. CeRh₂Si₂ with a tetragnal crystal structure shows an antiferromagnetic ordering and a metamagnetic transition in the magnetization curve for the field along the c-axis. A sudden change in the megnetostriction was observed at the field of 26 T where the metamagnetic transition occurs.

22CP38 paper-pdf

Non-Fermi-liquid behavior in CeNiGe_2-xSi_x single crystals

S.O. Hong^a, E.D. Mun^a, H.E. Takeda^c, M. Ishikawa^c, Y.S. Kwon^a,^b

^aBK21 Physics Research Division and Institute of Basic Science, Sungkyunkwan University, Suwon 440-746 Korea

^bCenter for Strongly Correlated Materials Research, Seoul National University, Seoul 151-742, Korea

^cInstitute for Solid State Physics, University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8581, Japan

CeNiGe₂ is known as a heavy Fermion antiferromagnetic compound with T_N=3.5K, while CeNiSi₂ is an intermediated valence material. We have investigated the specific heats in the series of CeNiGe_2-xSi_x from 0.5 to 35K. In transition region from a magnetic order to a nonmagnetic ground state, NFL phenomenon appears. We found that the temperature dependence of the specific heat obeys C/T µ lnT at x=1, which is characteristic of the non-Fermi-liquid behavior.

22CP39 paper-pdf

Transport and magnetic properties of CeCo_1-xNi_xGe₂ system

E.D. Mun^a, S.O. Hong^a, D.L. Kim^c, H.C. Ri^c, Y.S. Kwon^a,^b

^aBK21 Physics Research Division and Institute of Basic Science, Sungkyunkwan University, Suwon 440-746 Korea

^bCenter for Strongly Correlated Materials Research, Seoul National University, Seoul 151-742, Korea

^cKorea Basic Science Institute, Taejeon 305-333, South Korea

The electric resistivity and the magnetic-susceptibility have been measured for the series of intermetallic compounds CeCo_1-xNi_xGe₂ (x=0.1, 0.2, 0.5, 0.7, 0.8, 0.9, 1). CeNiGe₂ is the antiferromagnetic compound with T_N=3.5K. CeCoGe₂ is the intermediate-valence compound with the cerium valence varying from 3.2 at room temperature to 3.8 at 1.8K. The valance fluctuations are quenched at x=0.5, while the heavy Fermion behavior appears in x > 0.5.

22CP40 paper-pdf

Transport and magnetic properties of CeNiGe_2-xSi_x single crystals

S.O. Hong^a, E.D. Mun^a, H.E. Takeda^c, M. Ishikawa^c, Y.S. Kwon^a,^b

^aBK21 Physics Research Division and Institute of Basic Science, Sungkyunkwan University, Suwon 440-746 Korea

^bCenter for Strongly Correlated Materials Research, Seoul National University, Seoul 151-742, Korea

^cInstitute for Solid State Physics, University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8581, Japan

We have studied the rare-earth ternary system CeNiGe_2-xSi_x by magnetization and resistivity measurements. The series crystallize in a CeNiSi₂-type orthorhombic structure. CeNiGe₂ is the antiferromagnetic compound with T_N=3.5K, m_eff @ 2.56m_B and q_p=-102.6K while CeNiSi₂ is the intermediated valence system with the cerium valence varying from 3.3 at room temperature to 3.8 at T=1.8K. The properties of CeNiGe_2-xSi_x are determined by the competition of the Kondo and the RKKY interactions. This competition is dependent on the change of lattice volume, which gives rise to the change of hybridization.

22CP41 paper-pdf

Competition between Kondo effect and RKKY interaction modified by carrier concentration in Ce(Pd_1-xCu_x)₂Al₃

Peijie Sun^a, Yosikazu Isikawa^a, Qingfeng Lu^b, Tomohiko Kuwai^a, Dexuan Huo^a, Junji Sakurai^a

^aDepartment of Physics, Toyama University, Toyama 930-8555, Japan

^bDepartment of Physics, Henan Normal University, Henan 453002, China

A series of compounds Ce(Pd_1-xCu_x)₂Al₃ was synthesized in this work. The substitution of Pd by Cu resulted in an increase of carrier concentration as well as a decrease of lattice volume. Measurements of the electrical resistivity, the magnetic susceptibility and the specific heat were performed on this series to investigate the competition between Kondo effect and RKKY interaction. It was found that the antiferromagnetic property of CePd₂Al₃ changes abruptly to a ferro-like one at about x=0.2, and returns to the antiferromagnetic state with a continuous substitution. No evidence shows an enhancement of Kondo effect although the lattice volume is reduced.

22CP42 paper-pdf

Thermoelectric and Magnetic Properties of CeRh_1-xT_xSn (T=Co, Ni, and Ru) Alloys

Yuji Echizen, Kyotaro Yamane, Toshiro Takabatake

Department of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima,739-8530,Japan

CeRhSn is a valence fluctuating compound with a large thermopower of 60 mV/K at 150 K¹. We report on the thermopower S, electrical resistivity r, and magnetic susceptibility c of CeRh_1-xT_xSn (T=Co, Ni, and Ru; x £ 0.25) alloys. The Ni substitution changes c(T) to the Curie-Weiss type, whereas the Ru one to the Pauli-type. The maximum in S(T) is suppressed by all the substitutions. These results indicate that the coherence in the c-f hybridization plays the important role in the large thermopower of CeRhSn. ¹Bando et al., J. Alloys and compds. 313, 1 (2000).

22CP43 paper-pdf

Anisotropic Transport and Magnetic Properties of CeRhSn

M. S. Kim^a, Y. Echizen^a, T. Sasakawa^a, T. Suemitsu^a, K. Umeo^a, S. Kobayashi^a, M. Sera^a, T. Tayama^b, T. Sakakibara^b, T. Takabatake^a

^aDepartment of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima, 739-8530, Japan

^bInstitute for Solid State Physics, University of Tokyo, Kashiwa, 277-8581, Japan

CeRhSn with the quasi-Kagome lattice of Ce ions is a valence fluctuating compound². We have found strong anisotropy in both the resistivity (r_a > r_c) and magnetic susceptibility (c_c > c_a). The r_c(T) shows a strong anomaly below 10 K, where the c_c(T) exhibits a power law behavior. Below 8 K, an upturn is observed in C/T, the specific heat divided by temperature. These results suggest the presence of low-energy excitations at ~ 0.5 meV in CeRhSn.

22CP44 paper-pdf

De Hass-van Alphen effect of CeRhIn₅ under pressure

Hiroaki Shishido^a, Rikio Settai^a, Shingo Araki^a, Taiki Ueda^a, Yoshihiko Inada^a, Hisatomo Harima^b, Yoshichika [`(O)]nuki^a

^aGraduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan

^bThe Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan

We have studied quasi-two dimensional compounds LaRhIn₅ and CeTIn₅(T: Co, Rh) via the de Hass-van Alphen (dHvA) effect. The main Fermi surface in CeRhIn₅ is approximately the same as that in LaRhIn₅. The 4f electron in CeRhIn₅ is thus concluded to be localized, which is compared to an itinerant 4f-electron in CeCoIn₅^[1]. We have also studied the dHvA effect of CeRhIn₅ under pressure. The volume of the Fermi surface is unchanged as a function of pressure, but the cyclotron effective mass increases rapidly above 1GPa.

[1] H.Shishido et al. ; J. Phys. Soc. Jpn. 71 (2002) 162

22CP45 paper-pdf

Magnetic and superconducting properties under high pressure in URu₂Si₂

Gaku Motoyama, Yasuhisa Ushida, Takashi Nishioka, Noriaki K. Sato

Department of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan

Recent NMR measurement has suggested a phase separation; a paramagnetic and an antiferromagnetic phase coexist below T₀ = 17.5 K, and the volume fraction of the antiferromagnetic phase increases with pressure. We have measured ac magnetic susceptibility and thermal expansion under pressure for a well-characterized single crystalline sample. We observed an additional anomaly below T₀ that appears only under pressure. We will report these experimental results and discuss them on the basis of aforementioned phase separation model.

22CP46 paper-pdf

Transport properties in UCoAl under uniaxial pressure

Shanta R. Saha^a, Hitoshi Sugawara^a, Takahiro Namiki^a, Yuji Aoki^a, Hideyuki Sato^a, Tatsuma D. Matsuda^b, Y. Haga^b, E. Yamamoto^b, Y. ¯Onuki^b

^aDepartment of Physics, Tokyo Metropolitan University, Minami-Ohsawa 1-1, Hachioji, Tokyo 192-0397, Japan

^bAdvanced Science Research Center, JAERI, Tokai, Ibaraki 319-1195, Japan

UCoAl, a unique 5f electron compound, exhibits a metamagnetic transition around a magnetic field B_c ~ 1 T along c-axis from a paramagnetic ground state, reflecting the anisotropic 5f ligand hybridization. Under the hydrostatic pressure, B_c increases, i.e., metamagnetism is suppressed towards a paramagnetism. In a very recent magnetic measurement under uniaxial pressure (P_u) along c-axis ferromagnetism is found to appear in zero field. We report the transport properties in which B_c is found to increase for P_u along a-axis, possibly indicating an enhancement of 3d-5f hybridization in the basal plane.

22CP47 paper-pdf

Resistivity of Ce(Ru_0.85Rh_0.15)₂Si₂ under pressure

Tomohito Nakano^a, Kaoru Fujita^a, Shigeyuki Murayama^a, Kensuke Hoshi^a, Yoshiya Uwatoko^b, Masato Hedo^b

^aMuroran Institute of Technology, Muroran 050-8585 Japan

^bInstitute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan

Heavy fermion compound Ce(Ru_1-xRh_x)₂Si₂ shows a Spin Desity Wave (SDW) transition for 0.03 < x < 0.35 and shows a hump-type jump in resistivity along the tetragonal c-axis. We performed resistivity measurement under hydrostatic pressure for x=0.15 for 0.5K T 50K that has the highest T_N( ~ 5.5K). The hump-type jump in resistivity shifts to lower temperature with increasing pressure, at finally, disappears above P=1.0GPa. This fact indicates that the SDW phase is collapsed by pressure. On the other hand, the broad peak corresponding to the Kondo effect exists around T ~ 20K, and shifts to higher temperature with increasing pressure, indicateing increase of T_K.

22CP48 paper-pdf

The Fermi Surface in the "Kondo Semiconductor" CeNiSn

Taichi Terashima^a, Chieko Terakura^a, Shinya Uji^a, Haruyoshi Aoki^b, Yuji Echizen^c, Toshiro Takabatake^c

^aNational Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan

^bCenter for Low Temperature Science, Tohoku University, Sendai, Miyagi 980-8578, Japan

^cDepartment of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima 739-8530, Japan

Although there is plenty of convincing evidence for gap formation at low temperatures in CeNiSn, it has frequently been suggested that the gap is actually a pseudogap with finite density-of-states (DOS) at the Fermi level.³ We have found Shubnikov-de Haas oscillations in magnetoresistance measured on high-quality single crystals, thus producing an unambiguous proof of intrinsic finite DOS. The quasiparticle mass is fairly large, 10-20 m_e, suggesting electron-correlation effects. We also show that the resistivity at zero field follows a T² law, characteristic of a Fermi liquid, but with an anomalously large coefficient.

22CP49 paper-pdf

Anisotropic Magnetic Behavior of GdBa₂Cu₃O_6+y Single Crystals

Vladimir N. Narozhnyi^a,^b, Dieter Eckert^a, Günter Fuchs^a, Vladimir Nekvasil^c, Karl-Hartmut Müller^a

^aInstitut für Festkörper- und Werkstofforschung Dresden e.V., 270116, D-01171 Dresden, Germany

^bInstitute for High Pressure Physics, Russian Academy of Sci., Troitsk, Moscow Reg., 142092, Russia

^cInstitute of Physics, Czech Academy of Sci., Cukrovarnická 10, 16253 Praha 6, Czech Republic

Magnetic properties of the high-quality Al-free nonsuperconducting GdBa₂Cu₃O_6+y (Gd-1236) single crystals grown by flux method have been studied. Magnetic anisotropy below Néel temperature T_N » 2.3 K corresponds to the direction of Gd³⁺ magnetic moments along tetragonal c-axis. At T < T_N clear indications on spin-flop transitions for H||c have been observed on magnetization curves at H_sf » 10 kOe. Magnetic phase diagrams have been obtained for H||c as well as for H^c. A pronounced anisotropy in the magnetic susceptibility (unexpected for Gd-based compounds) has been found above T_N. Possible reasons for the observed anisotropic behavior of Gd-1236 will be discussed.

22CP50 paper-pdf

Randomness Effects on the Ferromagnetism of the Double Exchange Model

Nobuo Furukawa^a, Yukitoshi Motome^b

^aDepartment of Physics, Aoyama Gakuin University, Setagaya, Tokyo 157-8572, Japan

^bERATO-SSS, JST, Tsukuba, Ibaraki 305-8562, Japan

Magnetic properties of the double-exchange model in the presence of randomness are investigated. Spin excitation spectrum is calculated using the spin wave approximation, which shows anomalies such as broadening, anti-crossing and gap opening. The anomalies qualitatively reproduce the spin excitation spectrum in colossal magnetoresistance manganites with relatively low Curie temperatures. We also study critical phenomena using the Monte Carlo technique. Our results suggest that the destabilization of the ferromagnetism due to randomness is more rapid than the previous predictions by the coherent-potential approximation. Finally, we discuss that randomness control is an important notion to understand effects of the A-site substitution which has previously been considered as the bandwidth control.

22CP51 paper-pdf

Theoretical study of orbital excitations observed by resonant inelastic x-ray scattering in doped manganites

Hiroshi. Kondo^a, Kenji. Tsutsui^a, Sumio. Ishihara^b, Sadamichi. Maekawa^a

^aInstitute for Materials Research, Tohoku University, Sendai 980-8578, Japan

^bDepartment of Physics, Tohoku University, Sendai 980-8578, Japan

In order to examine the orbital excitations, we study the resonant inelastic x-ray scattering (RIXS) in doped manganites with and without orbital orderings. The RIXS spectra for orbital excitations are calculated by using the mean field approximation and the exact diagonalization method in a finite-size cluster. It is shown that the RIXS spectra in doped manganites show a more remarkable momentum dependence rather than the spectra in LaMnO₃. We find that the RIXS spectra are sensitive to both the orbital and spin structures. In particular, the momentum and polarization dependence of the spectra are examined in detail by changing orbital ordered states.

22CP52 paper-pdf

Orbital ordering and fluctuation in Perovskite Titanates

Tomohiko Hatakeyama^a, Sumio Ishihara^b, Sadamichi Maekawa^a

^aIMR,Tohoku University, Sendai 980-8577 Japan

^bDepartment of Physics, Tohoku University Sendai 980-8578 Japan

In perovskite titanates RTiO₃ where R indicates a trivalent rare-earth ion, it is well known that the triply degenerate t_2g orbitals are active and the orbital orderings are experimentally observed. We examine the orbital ordering and fluctuation in perovskite titanates by using the mean field approximation. Because of the three fold degeneracy of the orbital, there are multi-components of the orbital order parameter and the corresponding fluctuations. We find that, in this consequence, the successive orbital ordering occurs with changing temperature. This is in contrast to the system with the doubly degenerate orbital, such as perovskite manganites.

22CP53 paper-pdf

Cu-O-Cu Bond-Angle Dependence of Magnetic Interactions in Antiferromagnetic Cuprates

T. Shimizu^a, T. Matsumoto^a, A. Goto^a, K. Yoshimura^b, K. Kosuge^b

^aNano-materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan

^bDepartment of Chemistry, Kyoto University, Kyoto 606, Japan

We present an experimental evidence for systematics to show the bond-angle dependence of the supertransferred hyperfine interaction and of the superexchange interaction in Cu - O - Cu bonds with the bond-angle ranging from 90 to 180 degrees. Both interactions in cuprates exhibit much more sensitive dependence on the bond-angle rather than on the atom distance.

22CP55 paper-pdf

On the tilted low temperature antiferromagnetic structure in Cr₂O₃.

Sergei S. Krotov, Alexei V. Lisnyak

Moscow State University, Leninskie Gori, 119899 Moscow, Russia

When considering the low temperature behavior of magnetoelectric Cr₂O₃ the existence of G-type collinear antiferromagnetic structure with L-vector fixed along 3-fold axis was common knowledge. The detailed consideration of higher order magnetic anisotropy in the enthalpy of the system showed that even in the absence of the external magnetic field the antiferromagnetic vector L is inclined to the easy axis and as a result the longitudinal magnetic susceptibility in the zero-temperature limit doesn't vanish. The latter is in accord with a great number of experimental results.We have also discovered peculiar magnetoelectric behavior of the system under consideration in the low temperature region.

22CP56

Stripes and Superstructures in Manganites: the Role of Elastic Interactions

Daniil I. Khomskii^a, Kliment I. Kugel^b

^a Laboratory of Solid State Physics, Groningen University, Nijenborgh 4, 9747 AG Groningen, The Netherlands

^b Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Izhorskaya Str. 13/19, 127412 Moscow, Russia

The role of elastic interactions between Jahn-Teller ions in formation of various orbital- and charge-ordered structures in manganites and related compounds is analyzed. It is shown that such interactions alone are often sufficient to reproduce the structures observed in different regions of the phase diagram. A special attention is focused on stripe structures at high doping levels.

22CP57 paper-pdf

Effects of impurities on the magnetic property in copper oxides

Daisuke Matsunaka^a, Hideaki Kasai^a, Hiroshi Nakanishi^a, Ayao Okiji^b

^aDepartment of Applied Physics, Osaka University, Suita, Osaka 565-0871, Japan

^bWakayama National College of Technology, Gob¯o, Wakayama 644-0023, Japan

We study effects of impurities, e.g., nonmagnetic impurity atoms substituted for Cu atoms and oxygen vacancies, on the normal states in the CuO₂ planes of copper oxides, on the basis of the d-p model. The impurity potential is taken account of within the single-site coherent potential approximation and the Coulomb repulsion at each Cu site is treated by the fluctuation-exchange approximation. The spin susceptibility is calculated as a function of the concentration of the impurity. In the lecture, we will discuss about effects of impurities on the magnetic property of the CuO₂ plane from the obtained results.

22CP58 paper-pdf

Resistance and Thermal Expansion Anomaly near the Martensitic Transformation in GdCu under Pressure

Masashi Ohashi^a, Atsushi Tashiro^a, Gendo Oomi^a, Almudena Señas^b, J. Rodríguez Fernández^b, J.C. Gómez Sal^b

^aDepartment of Physics, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan

^bDepartamento de Ciencias de la Tierray F\acute\isica de la Materia Condensada, Universidad de Cantabria, 39005 Santander, Spain

GdCu undergoes a martensitic transition evolving from the CsCl structure at room temperature to the FeB structure as decreasing temperature. In the present work, we report the thermal expansion and electrical resistivity of GdCu under pressure. A large anomaly at 239 K, indicating the transition temperature Ms, is observed in the thermal expansion at ambient pressure. Ms rapidly decreases by applying pressure at a rate of dMs/dP ~ -160 K/GPa.

22CP59 paper-pdf

Unusual Impurity Effects on the Dielectric Properties of CaCu_3-xMn_xTi₄O₁₂

Wataru Kobayashi, Ichiro Terasaki

Department of Applied Physics, Waseda University, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo 169-8555, Japan

CaCu₃Ti₄O₁₂ has a large dielectric constant (e ~ 10⁴ at 300 K), which is almost constant above 100 K, followed by a 100-fold reduction below 100 K. Since no other dielectric materials have such properties, the physical mechanism has been extensively investigated. We found that only 2% substitution of Mn for Cu dramatically quenches the huge e of 10⁴ down to 100 over the measured temperature range from 4 to 300 K. In usual substitution effects, 2% impurity induces a tiny change in e of the order of 2%. Thus the present substitution effect suggests that dipole moments interact (probably frustrate) in CaCu₃Ti₄O₁₂, which is broken by a small amount of impurities.

22CP60 paper-pdf

Out-of-plane dielectric constant of q-(BEDT-TTF)₂RbZn(SCN)₄ single crystal

Koichi Inagaki^a, Ichiro Terasaki^a, Hatumi Mori^b

^aDepartment of Applied Physics, Waseda University, Tokyo 169-8555, Japan

^bInstitute of Solid State Physics, The University of Tokyo, Kashiwa 277-8518, Japan

The out-of-plane dielectric constant e of the quasi-two-dimensional organic conductor
q-(BEDT-TTF)₂RbZn(SCN)₄, which exhibits a metal-insulator transition at 190K, was measured and analyzed from 120 to 300K in the frequency range of 10³-10⁹ Hz. Most unexpectedly in the metallic state above 190K, e shows a significant dielectric relaxation, which is seriously incompatible with the Drude model that successfully explains e for usual metals. This suggests that above 190K insulating and metallic phases coexist, and some kind of charge inhomogeneity plays an important role in the metallic state.

22CP61

Low temperature specific heat of polyaniline and HCl doped nanotubes

J. L. Luo^a, Z. J. Chen^a, J. Zhang^a, M. X. Wan^b

^aInstitute of Physics, Chinese Academy of Sciences, Beijing100080, China

^bInstitute of Chemistry, Chinese Academy of Sciences, Beijing100080, China

The specific heat C of insulator polyaniline (PANI) and conducting HCl doped polyaniline (PANI-HCl) have been measured between 1.8 and 50K using thermal-relaxation method. At lower temperatures(T < 6K), the specific heat of PANI behaves as bT³, whilst that of PANI-HCl behaves as gT + bT³. The existence of linear term gT in the specific heat of conducting PANI-HCl is suggested due to the electronic contribution. At higher temperature, the lattice specific heat can not be described by Debye model. The excess part may due to the additional vibrational states besides the acoustic phonons as found in other polymer.

22CP62 paper-pdf

THz Radiation from Charge-Ordered Manganite Excited by Ultrafast Optical Pulses

Noriaki Kida, Masayoshi Tonouchi

Research Center for Superconductor Photonics, Osaka University, Suita, Osaka 565-0871, Japan.

The rapid progress of a THz-pulse generation and detection system has been made by using semiconductors excited by femtosecond optical pulses and by the subsequent discovery of THz radiation from new class of materials including quantum wells and superconductors. Another candidate materials are strong correlated electron systems like manganites due to their sensitive responses by external stimuli. Here we describe the first finding of THz radiation from magnetoresistive manganite Pr_0.7Ca_0.3MnO₃ thin films by femtosecond optical pulses. We emphasis that THz radiation from magnetic materials has not been observed so far. In this work, we provide the detailed THz radiation characteristics as a function of external stimuli and point out the photo-induced spin modulation as a source of THz radiation.

22CP63 paper-pdf

Memory Effects for Glass-like States of Solid N₂-Ar Mixtures.

S. Pilla^a, Jaha A. Hamida^b, Khandker Muttalib^b, Neil S. Sullivan^b

^aDepartment of Physics, University of California, San Diego, CA, U.S.A.

^bDepartment of Physics, University of Florida, Gainesville, FL 32611, U.S.A.

The results of high sensitivity dielectric measurements are reported for solid N₂-Ar mixtures for N₂ concentrations 49 < x(N₂) < 100 mole %. The observations indicate the onset of memory effects for the dielectric susceptibility on thermal cycling to temperatures below 30 K. The temperature dependence of the dielectric susceptibilities in this low temperature regime are observed to be frequency dependent, even for pure N₂ samples. These observations are consistent with a departure from ergodicity associated with the trapping of the systems in small regions of a configuration space characterized by a frustration-induced rugged free energy landscape.

22CP64 paper-pdf

Ultrasonic Study on Superconducting HoNi₂B₂C and Ho_0.75Y_0.25Ni₂B₂C

Miki Suetake^a, Yoko Takahashi^a, Masaru Suzuki^a, Kohji Abe^a, Kichizo Asai^a, Kazuhiko Kuroki^a, Susumu Isida^b, Hiroyuki Takeya^b

^aThe University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan

^bNational Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan

We performed the ultrasonic measurements for HoNi₂B₂C and Ho_0.75Y_0.25Ni₂B₂C single crystals as a function of temperature and magnetic field. In zero magnetic field, C₆₆ for HoNi₂B₂C showed a remarkable softening from more than 80 K while (C₁₁ - C₁₂)/2 remained almost constant. For the field applied along the a(b)-axis, softening of C₆₆ was suppressed. This behavior is related to the tetragonal to orthorhombic transition associated with the antiferromagnetic order. A similar softening of C₆₆ was also observed for Ho_0.75Y_0.25Ni₂B₂C.

22CP65 paper-pdf

Theoretical Classification of Two-Dimensional Organic Conductors

Chisa Hotta

RIKEN, 352-0298, Saitama, Japan

Several different polytypes have been found in the family of quasi-two-dimensional organic conductors, designated in Greek letters, e.g. q, k, which exhibit characteristic ground states quite different from each other. We present a new unified scheme to classsify these polytypes; all of them are mapped on an anisotropic triangular lattice model, where the systematic characterization is made by the newly introduced band structural parameters. Our theoretical calculations based on the above model including the on-site and inter-site Coulomb interactions indicate the actual relavance of these parameters to the ground state nature.

22CP66 paper-pdf

Effects of doping and oxygen partial pressure on electrical and optical properties of Mg(In_2-xAg_x)O₄ system

Y. S. Wang, S. C. Chou, M. F. Tai, M. W. Lee

Department of Physics, Chung Cheng University, Chia-Yi, Taiwan 621, R.O.C.

Transparent conducting oxides were widely used as transparent electrodes of flat plane displays due to its lower electrical resistivity and higher optical transmittance. The magnesium indium oxide MgIn₂O_4-d has been demonstrated to be one of the promising new transparent conductive oxides. In this report, Mg(In_2-xAg_x)O_4-d system with x = 0 - 0.5 were prepared by the standard solid-state reaction technique in various flowing gas. The effects of the Ag doping on structural,transport and optical properties are investigated. A single phase of the inverse-spinel-type MgIn₂O₄ structure was observed in all samples by the X-ray diffraction patterns. The phase is a cubic structure of the space group Fd-3m(No.227). But this doping can largely reduce the annealing time and decrease the annealing temperature.

22CP67 paper-pdf

Infrared properties of W-doped charge-density-wave material K_0.3MoO₃

T. Feng^a, N. L. Wang^a, Z. J. Chen^a, M. L. Tian^b, Y. H. Zhang^b

^aInstitute of Physics, Chinese Academy of Sciences, P. O. Box 2711, Beijing 100080, P. R. China

^bStructure Research Laboratory, University of Science and Technology of China, Hefei 230026, P. R. China

The reflectance and conductivity spectra of quasi-one dimensional compounds K_0.3Mo_1-xW_xO₃ (x=0, 0.03 and 0.15) have been studied over a broad frequency from far infrared to visible light region. While the dc resistivity measurements indicate no sign of CDW transition in heavily W-doped blue bronze, the optical conductivity spectra still show a single particle gap at around 0.2 eV for E parallel to the conducting chain direction which is usually considered as a typical feature associated with CDW condensate. Such impurity effect challenges our understanding about the occurrence of the gap with the CDW transition.

22CP68 paper-pdf

Control of Spin-Wave Instability Threshold in YIG Sphere

Michinobu Mino, Misako Yamazaki, Masayuki Tsukamoto, Hitoshi Yamazaki

Department of Physics, Faculty of Science, Okayama University, Tsushima-naka 3-1-1 Okayama 700-8530, Japan

Spin-wave instability threshold under multiple drive excitations is studied in an yttrium iron garnet sphere at 4.2K. Both a DC magnetic field and a pulsed parallel RF field are applied along the [111] direction. This parallel RF field parametrically excites spin-waves. Another perpendicular RF field, which is generated by a one-turn coil, excites magnetostatic modes. Interactions between spin-waves and magneostatic modes cause a change of an instability threshold. These phenomena provide information about nonlinear interactions in a nonequilibrium spin-wave system.

22CP69 paper-pdf

Relaxation time of parametrically excited magnetostatic mode in YIG

Masayuki Tsukamoto^a, Michinobu Mino^b, Hitoshi Yamazaki^b

^aGraduate school of Natural Science, Okayama University

^bDepartment of physics, Faculty of Science, Okayama University

Parallel pumping experiments were conducted on a single crystal yttrium-iron-garnet sphere. Microwave radiation from magnetostatic modes, which were parametrically excited through parallel pumped spin-waves, was studied experimentally at several temperatures. As excitation microwave power is turned off, it will be thought that microwave radiation decreases exponentially. Relaxation time of a magnetostatic mode, which is excited beyond thermal equilibrium level, is estimated by this method. We report temperature dependence of relaxation times.

22CP70 paper-pdf

Exact Diagonalization for the Vibronic Levels of Dynamic Yahn-Teller Systems -E_g Orbitals with e_g modes in Trigonal Fields -

Hisatsugu Yamasaki, Yuhei Natsume

Graduate School of Science and Technology, Chiba University, Inage-ku, Chiba 263-8522, Japan

We calculate the electronic states of degenerate E_g orbitals of d-leves in transition-metal ions coupled with vibrational modes of e_g expressed as Q₁ and Q₂. This is the typical system of dynamic Jahn-Teller effects(DYTE). In fact, vibronic levels has been calculated [1] in rather small dimensional Hamiltonian matrices(H). Further, the effect of the trigonal fields expressed as A(Q₂³ - Q₁² Q₂ ) on some low-lying levels has also investigated [2]. Here, we perform exact diagonalizations of H, without approximations used in previous work [1,2]. As results, we can diccuss clearly DYTE observed in magnetic compunds.

[1]H.C.Longuet-Higgins et al, Proc.Roy.Soc.A244(1958)1.

[2]M.C.M.O'Breien, Proc.Roy.Soc.A281(1964)323.

22CP71 paper-pdf

Phase Transition of a Coulomb System on a Lattice

Arnulf Möbius, Ulrich K. Rößler

Leibniz Institute for Solid State and Materials Research Dresden, PF 27 01 16, D-01171 Dresden, Germany

The possible existence of a phase transition in the Coulomb glass has been under controversial debate for many years. We approach this problem considering a lattice half-filled with localised particles which interact via the long-range Coulomb potential (without static disorder). Our numerical simulations focus on the temperature dependences of the specific heat and of the susceptibility related to the staggered occupation. They show the presence of a phase transition in two- and three-dimensional systems. Surprisingly, the critical behaviour of two-dimensional samples, obtained by a finite-size analysis, resembles that of the Ising system with short-range interaction. The phase transition seems to persist if a small static disorder is added.

22CP72 paper-pdf

Numerical renormalization study on magnetic properties of edge states in nanographite ribbons and carbon nanotubes

Toshiya Hikihara, Xiao Hu

National Institute for Materials Sciences, Sengen 1-2-1, Tsukuba 305-0047, Japan

Magnetic properties of nanographite ribbons (NGRs) and carbon nanotubes (CNTs) with open edges are investigated. A p-electron network in NGRs and CNTs with zigzag edges exhibits strongly localized edge states, which are expected to exhibit peculiar magnetic properties. In this work, we study the effect of the electron-electron interaction on the low-energy properties of the systems using the density-matrix renormalization-group method, which allows us to obtain highly accurate results. We show that effective spins grow around the zigzag edges of the NGRs and the open ends of zigzag CNTs. A schematic picture representing the low-energy physics of nanographite systems is proposed. We also discuss possible applications of the results.

22CP73 paper-pdf

The elastic properties of silica aerogels between 400 mK and 400K

David Daughton, James MacDonald, Norbert Mulders

Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA

Using an acoustic resonance spectroscopy technique, we have measured the elastic properties of a range of silica aerogels between 400 mK and 400 K. Similar to what has earlier been observed at ultrasonic frequencies, both bulk and shear moduli show a large decrease with temperature around 100 K. This is accompanied by damping peak, and can be contributed to thermally activated relaxation. Above 100 K we find a linear increase in the elastic moduli, which we attribute to rubber-like behavior, i.e., the elastic behavior is governed by entropic effects rather than energetics. Surprisingly, the increase in elastic moduli is not observed in the ultrasonic experiments. 1)Y. Xie and J.R. Beamish, Phys. Rev. B 57, 3406 (1998).

22CP74 paper-pdf

High frequency ESR measurement on molecular oxygen using pulsed high magnetic field

Shojiro Kimura, Koichi Kindo

KYOKUGEN, Osaka University, Machikaneyama 1-3, Toyonaka, Osaka 560-8531, Japan

High field/high frequency ESR measurement on molecular oxygen, of which electronic ground state is ³S state with S=1, has been performed in its gas phase at the frequencies 730.5GHz and 1017.6GHz using pulsed high magnetic field. The observed ESR signals are analyzed by the theory of Tinkham and Strandberg including the coupling between the spin and the rotational angular momentums of the molecule. The Paschen-Back effect in high field limit, predicted by the theory, is observed.

22CP75 paper-pdf

Thermal Contact to Lithium Metal

Juha Tuoriniemi, Kirsi Juntunen, Johanna Uusvuori

Low Temperature Laboratory, Helsinki University of Technology, P.O.Box 2200, FIN-02015 HUT

Experiments at ultra-low temperatures require very low thermal contact resistances, a serious issue even for metallic specimens below 1 mK. Customary practices include pressed contacts or welding by some means, e.g. diffusion welding. When dissimilar metals are joined, one must avoid excess formation of an alloy, usually a poor thermal conductor. The most firm contact with possibly deep alloying does not always have the best thermal conductivity. We have studied this problem when pressing lithium metal to contact with copper, silver and gold. The results are surprisingly different - good contacts could be produced only between Li and Cu, not with Li and Ag or Au. This is obviously due to easy alloying of Ag and Au with Li even at room temperature. This information is essential for proper materials choice in our planned experiment on superconductivity and nuclear magnetism on lithium metal.

22CP76

Non-phonon low-temperature thermal conductivity in clathrate semiconductors

D. A. Parshin, C. Laermans, M. A. Parshin

K.U. Leuven, Dept. of Physics, Celestijnenlaan 200D, 3001 Leuven, Belgium

In a recent paper Cohn et al., Phys.Rev.Lett., 82, 779 (1999) report an observation of low-temperature (LT) glasslike ( ~ T²) heat conduction in semiconductors Sr₈Ga₁₆Ge₃₀ with type-I clathrate hydrate crystal structure. This behavior was attributed to phonon scattering by a broad distribution of two-level systems (TLS's). The experiment was carried out on polycrystalline samples with typical grain size around 10mm. Our simple estimates however show that in such a case at T < 1K the mean free path of phonons should be limited by boundary scattering inside single grains and not by resonant scattering on TLS's. Therefore we conclude that the observed LT thermal conductivity might be of non-phonon origin and rather due to the long-range interaction between dopant ions of Sr in big 24-vertex polyhedral cages.

22CP77

On the origin of high-temperature elastic anomalies in k-(ET)₂X (X=Cu(NCS)₂, Cu[N(CN)₂]Br)

Masahito Yoshizawa, Takayuki Simizu

Department of Materials Science and Engineering, Iwate University, Morioka 020-8551, Japan

It has been known that k-type organic superconductors show elastic softenings below 100 K. The temperatures of the sound velocity minimum are 46 K and 37 K for k-(ET)₂Cu(NCS)₂ and k-(ET)₂Cu[N(CN)₂]Br, respectively. The origin of these softenings have not been made clear, yet. These salts show a Insulator-to-Metal (IM) crossover below 100 K. The sound velocity anomalies have been considered to correlate with these IM behavior. On the other hand, the importance of the antifetrro spin fluctuation and the role of superconductivity have been pointed out by some authors. We will give discussions on the origin of the elastic anomalies of these salts by providing model calculations based on a simple band picture, which has been succsessfully used for the interpretation of the elastic anomalis in heavy fermion systems.

22CP79 paper-pdf

Optically Pumped NMR in Semiconductor InP

Kenjiro Hashi^a, Atsushi Goto^a, Ryo Miyabe^b, Susumu Machida^c, Tadashi Shimizu^a, Giyuu Kido^a, Shinobu Ohki^c

^aNational Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan

^bDepartment of Physics, Science University of Tokyo, Tokyo, Japan

^cJapan Science and Technology Corporation, Tokyo, Japan

We have developed an optically pumped (OP) NMR system for semiconductors. A circularly polarized laser light pumps up the polarizations of the electron spins, which are transferred to the nuclear spins via hyperfine couplings resulting in a significantly enhanced NMR signal. We have performed OPNMR measurements on InP with several kinds of dopants (S, Sn, Zn and Fe), and confirmed that the efficiency of the signal enhancement of ³¹P strongly depends on the dopants. In the presentation, we will discuss the conditions for the effective OPNMR in InP.

22CP80

Doppler-shifted cyclotron resonance with Alfven waves in LaSb

Makoto Yoshida^a, Keiich Koyama^a, Takahiro Tomimatsu^a, Makoto Shirakawa^b, Akira Ochiai^b, Mitsuhiro Motokawa^a

^aInstitute for Materials Research, Tohoku University, Sendai 980-8577, Japan

^bCenter for Low Temperature Science, Tohoku University, Sendai 980-8578, Japan

Cyclotron resonance measurements on a single-crystal of LaSb have been performed in the temperature range from 1.6 to 40 K in the frequency range from 50 to 190 GHz. For magnetic fields parallel to the [100] direction, the determined effective masses are 0.20m₀, 0.17m₀, and 0.45m₀, which correspond to the a-branch, the b-branch, and the g-branch, respectively. In addition to the "normal" cyclotron resonance, we have observed anomalous absorption lines which show nonlinear behavior on the frequency-field diagram. The nonlinear behavior is explained by Doppler-shifted cyclotron resonance with Alfven waves. The anomalous cyclotron resonance has been observed for the first time in rare-earth compounds.

22CP81 paper-pdf

Low-Temperature Specific Heat in the Charge-Density-Wave State in ZrTe₃ and TaTe₄

Shujirou Mori^a, Yoshitoshi Okajima^b, Katuhiko Inagaki^a, Satoshi Tanda^a, Kazuhiko Yamaya^a

^aDeaprtment of Applied Physics, Hokkaido University, Sapporo 060-8628, Japan

^bAsahikawa National College of Technology, Asahikawa 071-8142, Japan

Low-temperature specific heat of chain conductors, ZrTe₃ and TaTe₄, measured between 1.5 K and 10 K, were found to exhibit an anomaly which deviates from a T³ law; an excess heat capacity contribution with a peak around T=5 K. This contribution was well described by a Debye dispersion of low-energy mode with two cutoff frequencies, the phason analog of the Debye temperature and the pinning gap. The origin is discussed in comparison to results observed in other CDW systems.

22CP82 paper-pdf

Scheme for the energy-band calculation under the external magnetic field

Katsuhiko Higuchi^a, Masahiko Higuchi^b

^aDepartment of Electrical Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan

^bDepartment of Physics, Tohoku University, Sendai 980-8576, Japan

The current-density functional theory (CDFT) provides a promising method for the calculations of the electronic structure of the system in external magnetic fields. In this paper, we propose three kinds of approximation schemes on the basis of the coupling-constant expression for the exchange-correlation energy functional. These should be called the CDFT version of the local-density approximation, average-density approximation and weighted-density approximation. The validity of these approximate forms is estimated by using the sum rules which we have recently derived. We also discuss the symmetry of the noninteracting fictitious system of the CDFT. It is shown that the magnetic Bloch electrons of the fictitious system have the same symmetry as the real system.

22CP83 paper-pdf

Lom-Temperature Cathodouminescnce of ZnO Films Grown by Various Methods

Yahya Alivov^a, Mikhail Chukichev^b

^aInstitute of Microelectronics Technology, Russian Academy of Sciences, Chernogolovka, Moscow district, Russia

^bDepartment of Physics, Lomonosov Moscow State University, Moscow, Russia

The 4.2 K temperature optical properties of the ZnO films grown by various methods are studied by cathodoluminescence (CL) spectroscopy. Polycrystalline and epitaxial ZnO films doped with Cu, Ga were grown by oxydation of the metallic Zn layers and by chemical vapor deposition methods respectively. Triplet structure of green band phonon replica in CL spectra of Cu-doped ZnO films has been observed, not earlier reported. It is shawn that the typical green emission of ZnO originate from not-controllable natural Cu centers as a result of annigilation of acceptor excitons [d10h ].

22CP84 paper-pdf

STS study of spectrum of surface electronic states in bismuth

V.S. Edelman, A.V. Ofitserov

P.L. Kapitza Institute for Physical Problems RAS, ul. Kosygina 2, Moscow 117334, Russia

The concentration of conduction electrons in bismuth is very low, their wavelength is much longer than the interatomic distance, so the interaction of conduction electrons with the surface should result in forming of an independent two-dimensional system of electrons near the surface.

We performed scanning tunneling spectroscopy of the basal trigonal plane (0001) and "quasitrigonal" plane of twin interlayer on bismuth surface. The existence of surface electronic states with spectra characterized by well defined features is established for both crystallographic surfaces. An analysis of these spectra gives an explicit evidence of the existence of two-dimensional layer of conduction electrons with usual metallic density of electronic states on bismuth surface.

22CP85

Magnetic Field Effects in Amorphous Solids at Ultra Low Temperatures

Lidiya Polukhina, Stefan Ludwig, Danna Rosenberg, Douglas Osheroff

Department of Physics, Stanford University, Stanford, CA 94305-4060, USA

A series of recent experiments has revealed a surprising magnetic field dependence of the dielectric constant in various multicomponent glasses at low temperatures. This dependence is not predicted by the two level system model of non-interacting tunneling centers in amorphous insulators. A rigorous theoretical explanation of the observed effects requires a systematic study of different glasses in a broad parameter range. We present the design of a ³He immersion sample cell which will enable us to examine up to 6 materials simultaneously. We plan to investigate the dielectric properties of samples in a temperature range from 1 K down to 4 mK with an applied magnetic field up to 8 Tesla and frequencies ranging from 100 Hz to 100 kHz. In addition, we hope to find an amorphous solid whose dielectric constant shows no magnetic field dependence, making it suitable for thermometry in applied magnetic fields.

22CP86

The electrical resistivity of single-crystalline Al free from size-effect

Isao Nakamichi^a, Takao Kino^b

^aCryogenic center, Hiroshima University, Higashi-Hiroshima 739-8526, Japan

^b Faculty of engineering, Hiroshima-Kokusai-Gakuin University, Hiroshima 739-0321, Japan

The electrical resistivity r of high-purity single-crystalline and polycrystalline Al was measured at 1.5-80K for plates with various thickness. The surface-caused T² resistivity is much greater on polycrystalline than single-crystalline plates. The temperature-dependent part of r,r(T), of bulk single crystal is found to be as follows. 1)r(T)=a_hT²+bT⁵ at 10 - 39K, where a_h=5.3 fWm/K² and b=1.9 aWm/K⁵. 2)r(T)=a_LT²+gT⁴ at 4 - 10K, where a_L=1.8 fWm/K² and g=64 aWm/K⁴.The values a,bandgagree with the theoretical ones for the electron-electron (e-e) scattering, the normal electron-phonon (e-p) scattering, and the umklapp e-p scattering, respectively. These show the existence of e-e scattering at 4-39 K and the transition on scattering mechanism around 10 K.

22CP87 paper-pdf

Anomalous low temperature diamagnetism in compounds and alloys

I.V. Svechkarev^a, V.A. Desnenko^a, S.N. Dolya^a, G.E. Grechnev^a, A.E. Baranovskiy^a, G.P. Mikitik^a, A. Czopnik^b

^aB.Verkin Institute for Low Temperature Physics and Engineering, Kharkov, 61103, Ukraine

^bW.Trzebiatowski Institute of Low Temperature and Structure Research, Wrocaw, 50-950, Poland

Applications of pronounced features of orbital magnetic susceptibility c, related to the bands degeneracy points in close vicinity of the Fermi level E_F, are demonstrated experimentally and theoretically. Characteristics of scattering and band structure can be revealed by realizing features of c with doping and temperature. Band degeneracy points at E_F were found to be responsible for the anomalous diamagnetism in CaPb₃ and YbPb₃ at low temperatures. In Al the degeneracy point is located just under E_F, and the diamagnetic anomalies were realized by doping of Al with Li and Zn. The appearance and damping of these anomalies of c with temperature, impurities, and quenched vacancies are discussed.

22CP88 paper-pdf

The ³He gas and paramagnetic substance interaction

G. Mamin^a, H Suzuki^a, M.S. Tagirov^b, V.N. Efimov^b

^aFaculty of Science, Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan

^bMRS laboratory, Kazan state university, Kremlevskaja 18, Kazan, 420008, Russia

We searched way for dynamical polarization of noble gas. We choose the coal prepared from carbohydrate as paramagnetic substance. This coal surface consist many paramagnetic centers (about 10²⁰ centers/m.) and the EPR line is very narrow at vacuum (for our sample dH=1 Oe). The EPR linewidth in system with absorbed ⁴He gas is also narrow (dH=1.7 Oe, at T=4.2K). In case absorbed ³He the linewidth increase to dH=4.3 Oe due to hyperfine interaction with ³He nuclear spin. Also the saturation of EPR line detected at microwave power 200mW. Spin-lattice relaxation time for ³He nuclears is about 400 mS at 1.7 K, instead 1-3 hour at pure 3He gas. So, the system consists coal paramagnetic centers and absorbed ³He gas can be used for dynamical polarization of noble gas.

22CP89 paper-pdf

Magnetic Field Dependent Atomic Tunneling in Non-Magnetic Glasses

S. Ludwig, C. Enss, S. Hunklinger

Kirchhoffinstitut für Physik, Universität Heidelberg, 69120 Heidelberg, Germany

The low-temperature properties of insulating glasses are governed by atomic tunneling systems (TSs). Recently strong magnetic field effects in the dielectric susceptibility have been discovered in glasses at audio frequencies at very low temperatures. Moreover, it has been found that the amplitude of two-pulse polarization echoes generated in non-magnetic multi-component glasses at radio frequencies and at very low temperatures shows a surprising non-monotonic magnetic field dependence. The magnitude of the latter effect indicates that virtually all TSs are affected by the magnetic field, not only a small subset of them. We have studied the variation of the magnetic field dependence of the echo amplitude as a function of the delay time between the two excitation pulses and find a systematic variation. This suggests that the evolution of the phase of resonant TSs is changed by the magnetic field.

22CP90 paper-pdf

Effect of radiation-induced defects on the high-field magnetoresistivity of compensated transition metals

V. V. Marchenkov^a, V. E. Arkhipov^a, H.W. Weber^b

^aInstitute of Metal Physics RAS, Kovalevskaya Str. 18, 620219 Ekaterinburg, Russia

^bAtomic Institute of the Austrian Universities, Stadionallee 2, A-1020 Vienna, Austria

The radiation-induced defects, produced in tungsten and molybdenum single crystals by electrons (E=5 MeV), protons (E=20 MeV) and krypton ions (E=305 MeV), were studied both by magnetoresistivity and by field-ion microscopy. The transverse magnetoresistivity of tungsten and molybdenum single crystals with a residual resistivity ratio of up to 80,000 was measured before and after irradiation in the temperature range from 4.2 to 80 K and in magnetic fields up to 15 T. We show that the radiation-induced defects strongly affect the high-field magnetoresistivity and can be used to obtain new information about the type of the radiation-induced defects.

22CP91 paper-pdf

Using experimental data to constrain theories of hopping conduction in NTD germanium

Adam L. Woodcraft, Rashmi V. Sudiwala

Department of Physics and Astronomy, University of Wales, Cardiff, CF24 3YB, UK

The mechanism for low temperature electrical conduction in neutron transmutation doped (NTD) germanium is believed to be variable range hopping (VRH). The resistance, R, at temperature T should then follow R(T)=R₀ exp(T₀/T)^p, for constant T₀, R₀ and p. NTD Ge is thought to have a ``Coulomb gap'' in the density of states; theories then generally predict p=0.5. However, some theories suggest larger values, such as p=0.55. So far, experimental results have failed to distinguish between these values of p. We show that it is practical to make sufficiently accurate measurements to do so. We present measurements for several NTD Ge samples with different doping levels, and discuss the various possible sources of error. We compare the results with the different theoretical predictions.

22CP92 paper-pdf

Low Temperature Properties of Lead Dioxide: NMR Study and Calculation of Zone Structure

Leonid Boyarsky^a, Sviatoslav Gabuda^b, Svetlana Kozlova^b

^aNovosibirsk State University, Novosibirsk, Russia

^bInstitute of Inorganic Chemistry, Novosibirsk, Russia

The NMR spectra of ²07Pb at room temperature and 20 K with field 9.1 T was measured for study the nature of the lead dioxide metallic behavior. There was shown that the inhomogeneous distribution of Oxygen ions take place, it lead to create a number of oxides. There was shown that the Knight shift value corresponds to metallic conductivity. The calculations of zone structure have been created with taken into account the relativistic effects that have allowed to find the Fermi level inside of the filled zone. The nature of metallic state of the lead dioxide connects both with peculiarities of the zone structure and with inhomogeneous distribution of charge density.

22CP93 paper-pdf

Neutron Scattering Facility for High Magnetic Fields up to 40 Tesla at Hahn-Meitner-Institut Berlin and Berlin Neutron Scattering Center (BENSC)

P. Smeibidl, M. Meissner, F. Mezei, K. Prokes, B. Schröder-Smeibidl, M. Steiner

Hahn-Meitner-Institut Berlin GmbH, BENSC, Glienicker Str. 100, D-14109 Berlin, Germany

The Hahn-Meitner-Institut has made great efforts to offer the users of its neutron scattering facilities at BENSC outstanding experimental conditions especially in sample environment: our possibilities range from experiments at high temperatures up to 1500 K to low temperatures down to 30 mK and high magnetic fields up to 14.5 T (for temperatures down to 1.5 K even 17 T). To further extend the range of continuous magnetic fields to be used for neutron scattering and because of limitations with superconducting technique, we have proposed a new facility with normal conducting magnets up to 40 T. The technical concept (40 MW power station, magnets, cooling circuit) is described as well as results and perspectives of neutron scattering experiments at high magnetic fields (e.g. correlations in HTSC's).

22CP94 paper-pdf

Self-Trapping Features of Excitons in Elastically Deformed Alkali Halides

Sagyn Tulepbergenov, Kuanyshbek Shunkeev, Igor Spivak-Lavrov

Aktobe State University, 463000 Aktobe, Kazakhstan

The self-trapping (ST) features of excitons in alkali halides (AH) are theoretically studied under both hydrostatical and uniaxial compressions. The variational calculations of the ground state energy of interacting exciton-phonon system in elastically deformed AH are carried out within the adiabatic approximation and the continuum model of ionic crystals. The results are discussed in terms of the stress-induced change of the exciton ST barrier. It is shown that the small hydrostatic and uniaxial compressions (which almost do not change the force constants) of AH lead to the decreasing of the exciton ST barrier. But at large hydrostatic pressure the force constants of AH, the bandwidth of excitons and the exciton ST barrier are noticeably increased. While the lowering of the lattice symmetry of AH under uniaxial stress leads to the decreasing of the exciton ST barrier.

22CP95

Dispersion of helicon-doppleron-phonon modes in strong coupling regime

Vladimir V. Gudkov

Russian State Vocational Pedagogical University, 11, Mashinostroiteley St., Yekaterinburg 620012 Russia

The third-order dispersion equation of strongly coupled helicon-phonon and doppleron-phonon modes equation is solved analitically using the Fermi surface model which earlier has been used for interpretation of experiments on doppleron dispersion in single crystal of superpure indium. The results of the model calculation show that the dispersion curves w = w(k) (w - frequency, k - wave vector) have two different types of gaps. The first one is formed by the crosspoint of the dispersion curves of ultrasonic and electromagnetic waves with identically directed group velocities while the second one - by the crosspoint of the curves related to waves with oppositly directed group velocities. Principal differencies of the gaps should be seen in experiments dealing with a shear ultrasonic wave propagation along the high-symmetry cryslallographic axis (C₃, C₄ or C₆) of a metal in a longitudinal magnetic field.

22CP96

Thermal activation processes and harmonic oscillator relaxation contribution to the sound velocity in neutron irradiated quartz

M. A. Parshin, C. Laermans, D. A. Parshin

K.U. Leuven, Dept. of Physics, Celestijnenlaan 200D, 3001 Leuven, Belgium

The behaviour of the low temperture (LT) sound velocity in glasses above the maximum is not well understood. In this work we study the variation of the LT ultrasonic velocity ( ~ 300 MHz) in neutron irradiated quartz (NIRQ) in the temperature region above the LT maximum. NIRQ is very attractive as a model for the glassy state since varying the neutron dose allows continuous structural variations from the perfectly ordered crystal to the amorphous network disorder and tunneling states can be induced systematically. We found that there is an indication for the contribution to the temperature dependence, not only from the tunneling states, but also from the thermal activation processes and the harmonic oscillators.

22CP97 paper-pdf

Nonlinear Dielectric Response of Low-Energy Excitations in Glasses

Peter G. Strehlow

Physikalisch-Technische Bundesanstalt, Abbestrasse 2-10, 10587 Berlin, Germany

The nonlinear dielectric response of low-energy excitations in glasses is investigated on the basis of the two-level tunneling model. It appears that the tunneling model has sufficient flexibility to explain the low-temperature dielectric response of glasses, at least qualitatively. An explicit analysis of experimental data obtained on borosilicate glasses leads to a low-energy cutoff D_0min/k » 2 mK in the density of tunneling states, which is consistent with recent heat capacity measurements. The strong dependence of the nonlinear dielectric response on static magnetic and time-dependent electric fields can be interpreted in a generalized tunneling model as quantum effect of electromagnetic fluxes in glasses at ultra-low temperature.

22CP98 paper-pdf

Far-infrared transient- resonant Faraday rotation induced by non-equillibrium electrons in compensated p-InSb under pulsed photo-excitation

Masato Suzuki^a, Hiromi Kobori^b, Nobuo Kotera^c, Ken-ichi Fujii^a, Tyuzi Ohyama^a

^aGraduate School of Science, Osaka University, 1-16 Machikaneyama, Toyonaka, Osaka 560-0043, Japan

^bDepartment of Physics Faculty of Science and Engineering, Konan University, Hyogo, 658-8501, Japan

^cDepartment of Computer Science and Electronics, Kyushu Institute of Technology, 820-8502, Japan

We have for the first time investigated resonant-transient Faraday effect induced by conduction and bound electrons in compensated p-InSb under pulsed-photoexcitation at 4.2 K with use of the far-infrared laser. The Faraday rotation angle is extremely sensitive to the refractive index for both circularly polarized lights. Ionized donors in compensated p-InSb are neutralized by pulsed-photoexcitation and the donor cyclotron resonance by these photo-excited impurities causes large change of refractive index of the sample. As photo-excited impurities recombine with finite lifetime, the refractive index is time-dependent.

22CP99 paper-pdf

Optical phonon localization in self-assembled Ge dots

Tzueng-Rong Yang, Mykhaylo M. Dvoynenko

Department of Physics National Taiwan Normal University, 88 Sec.4 Ting-Chou Rd., Taipei 117, Taiwan

We have separated a Ge-Ge vibration mode (nearly 300 cm^-1) from Si substrate Raman signal caused by two acoustic phonons. The obtained Raman spectra have different and nonsymmetrical lines broadened to low frequencies. The width of the line decreases with quantum dot hight. We have not observed Raman signal in the geometry. It means that investigated Raman signal is associated with by LO phonon only. Considering the Ge dots and wetting layer as a totality of independent linear chains of Ge atoms directed along [001], we have found out the broadening as result of optical phonon localization in Ge wetting layer and dots. The wetting layer thickness increases (from 4.5Å to 10Å) with Ge dot hight. We have estimated the strain in Ge system. The strain decreases (from 4% to 1.5%) with Ge dot hight. In spite of the Ge LO and Si LA bands overlap, there is the confinement effect for Ge LO phonons.

Footnotes:

¹S. V. Dordevic et al.: Phys. Rev. B 60 (1999) 11321.

²Bando et al., J. Alloys Comp. 313, 1 (2000).

³For a review, see, Takabatake et al., J. Magn. Magn. Mater. 177-181, 277 (1998)