Non-linear Conductivity in the Spin-Density Wave Phase of (TMTSF-d12)2ClO4
K. Nomuraa, T. Terazakia, A. Hoshikawaa, N. Matsunagaa, M. Watanabeb, S. Nakatsujib, J. Yamadab
aDivision of Physics, Hokkaido University, Sapporo 060-0810, Japan
bDepartment of Material Science, Himeji Institute of Technology, Kamigohri 678-1201, Japan
We have measured the non-linear conductivity in the spin-density wave (SDW) phase of (TMTSF-d12)2ClO4, which has deuterated TMTSF molecules, in order to investigate the sliding motion of SDW. We found the anion ordering at TAO=27K as a resistance drop. The rapid cooling of sample at TAO induces the SDW phase as a ground state. In this SDW phase we have observed the non-linear electric conductivity with the threshold electric field ET, associated with the sliding of SDW. The value of ET decreases monotonously with decreasing temperature. In addition, the SDW excess conductivity shows a sharp drop below 0.3TSDW. We discuss the mechanism of SDW sliding from these results.
Pressure Effect on the Structure of an spin-Peierls Substance:MEM-[TCNQ]2
Kouji Ejimaa, Takayuki Tajiria, Hiroyuki Deguchia, Masaki Mitoa, Seishi Takagia, Kenji Ohwadab, Hironori Nakaoc, Youichi Murakamic
aFaculty of Engineering, Kyushu Institute of Technology, Kitakyushu 804-8550, Japan
bSping-8, Koto Mikazuki-cho Sayo-gun Hyogo 679-5148, Japan
cFaculty of Science, Tohoku University, Sendai 980-8578, Japan
The temperature dependence of the magnetic susceptibility of an spin-Peierls substance, MEM-[TCNQ]2, shows an anomalous pressure effect. As the pressure increases, the susceptibility at low temperatures increases as if free magnetic spins are produced and it overwhelms the spin-Peierls transition. In order to clarify the pressure effect, the crystal structure of the material under pressure has been studied by using synchrotron radiation at KEK. The reflection resulting from the super lattice of the spin-Peierls state disappears under pressure and the structure is significantly affected even at room temperature.
Effect of Charge Ordering on Spin Peierls State in Low Dimensional Electron Systems
Muneo Sugiura, Yoshikazu Suzumura
Department of Physics, Nagoya University, Nagoya 464-8602, JAPAN
The spin Peierls (SP) state in the presence of charge ordering (CO) is examined for a Peierls- Hubbard model with a quarter-filled band, a bond dimerization and a nearest-neighbor repulsive interaction (V). By applying the renormalization group method to the bosonized Hamiltonian, the SP state is calculated by varying the magnitude of V. The CO appears for large V due to the commensurability energy at quarter-filling while the SP state is enhanced by the dimerization due to effectively half-filled band. It is found that, with increasing V, the SP state is strongly reduced indicating a transition into spin density wave (SDW) state at low energy scale. We discuss the relevance to the competition between the SP state and the SDW state in organic conductors, DCNQI salt and Bechgaard salt.
Magnetic excitations in the high-temperature phase of a¢-NaV2O5
Tetsuo Ohamaa, Masahiko Isobeb, Yutaka Uedab
aGraduate School of Science and Technology, Chiba University, Chiba 263-8522, Japan
bInstitute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan
The quarter-filled ladder compound a¢-NaV2O5 exhibits a charge ordering transition at Tc ~ 34K. In the high-temperature phase above Tc, magnetic excitations with quasi-one dimensional character are observed, but it is not understood how the charge fluctuation affects the magnetic excitations. We measured the nuclear spin-lattice and spin-spin relaxation rates at the V sites above TC. We will discuss the effects of the charge fluctuation on the temperature dependence of the nuclear relaxation rates.
Ground state of antiferromagnetic Heisenberg two-leg ladder
in terms
of the valence-bond solid picture
Munehisa Matsumotoa, Synge Todob, Chitoshi Yasudaa, Hajime Takayamaa
aInstitute for Solid State Physics, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa 277-8581, Japan
bTheoretische Physik, Eidgenössische Technische Hochschule, CH-8093 Zürich, Switzerland
We have proposed the plaquette-singlet solid (PSS) picture for the ground state of the spin-1 antiferromagnetic Heisenberg (AFH) two-leg ladder. Based on the PSS picture, we discuss the hidden order in the ground state of spin-1 AFH two-leg ladder and its correspondence to that in the ground state of spin-2 AFH chain by introducing the appropriate hidden order parameters and evaluating them by the quantum Monte Carlo method. When the bond alternation is introduced, there are quantum phase transitions and each phase can be identified with that in the dimerized spin-2 chain. We argue that the valence-bond solid picture of spin-2S AFH chain can be applied to the ground state of spin-S AFH two-leg ladder.
Spin-Hole Order in the 1-D Chain Cuprate Ca0.824CuO2
Masaaki Isobe, Koji Kimoto, Eiji Takayama-Muromachi
National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
The hole-doped edge-sharing Cu-O chain compound CaxCuO2 (x ~ 0.83) has a novel quantum electronic state where spatially modulated spin staggered moment coexists in a site with a spin-singlet ground state. It is important to solve the magnetic structure in the coexisting state, because it seems to be related to an electronic state of the under-doped region in high-TC cuprate superconductors.
We have studied the magnetic state from a viewpoint of crystallographic features of the compound, and determined a possible spin-hole arrangement in the coexisting state by precisely analyzing local structural distortion in the CuO2 chain using a modulated-crystal-structure analysis technique. The essential periodic sequence obtained is ···°¯¯°··· ( ¯: up- or down-spin, °: hole) along the chain.
Optical Absorption of S=1/2 Two-Leg Spin Ladder Systems
Nobuyasu Haga, Sei-ichiro Suga
Department of Applied Physics, Osaka University, Suita, Osaka 565-0871, Japan
We calculate the spectrums for the phonon-assisted optical absorption of the S=1/2 two-leg spin ladder systems, using continued fraction method based on the Lanczos algorithm. When the interchain interaction (J^) is larger than the intrachain interaction (J||); J^/J|| ³ 1, the peak structure appears in the lower energy region and the hump structure appears in the higher energy region of the spectrums along the leg. The former is caused by the S=0 two-magnon bound state, and the latter is caused by the two-magnon continuum. When J^/J|| < 1, the broad peak caused by the continuum becomes dominant. We further investigate the effects of a cyclic four-spin interaction (Jcyc). When J^/J|| = 1 and Jcyc=0.1, the spectral peak caused by the S=0 two-magnon bound state gets large as compared to that without a cyclic four-spin interaction.
The quasi-one dimensional diffusive motion of spin solitons in the spin Peierls state of (DMe-DCNQI)2Li
Maki Hiraokaa, Hirokazu Sakamotoa, Kenji Mizoguchia, Reizo Katob
aDepartment of Physics, Tokyo Metropolitan University, Minami Osawa, Hachioji, Tokyo, 192-0397,Japan
bRIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan
(DMe-DCNQI)2Li is a 1/4 filled spin Peierls (SP) system with Tsp ~ 65K. Enough below Tsp, it is known that Curie paramagnetism is observed. With electron spin dynamics by ESR, we found the Curie spins diffuse quasi-one dimensionally, implying existence of spin solitons which could arise from finite chain length separated by impurities. The concentration of spin solitons is estimated from the Curie spin susceptibility to be ~ 1%. The spin soliton diffusion is activated by phonons and follows T2 relation. An extent of the spin soliton is estimated to be about one unit. This narrow extent may be related to missing antiferromagnetic long range order, contrary to the doped CuGeO3 case.
Magnetization Plateaux in S=1 Organic Spin Ladder BIP-TENO
Tôru Sakaia, Nobuhisa Okazakib, Kiyomi Okamotoc, Koichi Kindod, Yasuo Narumid, Yuko Hosokoshie, Keiichi Katohe, Katsuya Inouee, Tsuneaki Gotof
aDepartment of Physics, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan
bFaculty of Science, Himeji Institute of Technology, Kouto, Kamigori, Ako-gun, Hyogo 678-1297, Japan
cDepartment of Physics, Tokyo Institute of Technology, Megro-ku, Tokyo 152-8551, Japan
dKYOKUGEN, Osaka University, Toyonaka, Osaka 560-8531, Japan
eInstitute for Molecular Science, Okazaki, Aichi 444-8585, Japan
fInstitute for Solid State Physics, University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
We show a clear experimental evidence of the 1/4 plateau in the high-field magnetization measurement on the first-synthesized S=1 organic spin ladder compound BIP-TENO. The theoretical mechanism of the plateau formation is also proposed, based on the frustration due to the long-range exchange interactions.
Symmetry Control of the Spin Hamiltonian of the Haldane compound Ni ( C2 H8 O4 )2 NO2 ( Cl O4 ) under Uniaxial Pressure
Takehiro Kinoshita, Masaki Mito, Tatsuya Kawae, Kazuyoshi Takeda
Department of Applied Quantum Physics, Kyushu University, Fukuoka 812-8581, Japan
We have measured the magnetic susceptibility c(T) of the Haldane compound Ni ( C2 H8 O4 )2 NO2 ( Cl O4 ) (NENP) under uniaxial pressure P. When P is applied along the uniaxial anisotropy D, the system preserves the O(2) symmetry under uniaxial pressure. For P ^D, however, the system tends to crossover from the O(2) symmetry to the SU(2) symmetry, similar to the experimental results for hydrostatic pressure by Zalianyak et al.1. Within our experimental range of uniaxial pressure up to about 1 kbar, we have not observed any anomaly corresponding to the three-dimensional magnetic long range ordering and quantum phase transition.
Spin-Peierls Mechanism for the Non-Trivial Magnetization Plateaux in Two-Leg Spin Ladders
Kiyomi Okamotoa, Tôru Sakaib
aDepartment of Physics, Tokyo Institute of Technology, Oh-okayama, Meguro-ku, Tokyo 152-8551, Japan
bDepartment of Physics, Tohoku University, Aoba-ku, Sendai, 980-8577, Japan
We propose the spin-Peierls mechanism for the non-trivial magnetization plateaux in S=1/2 and S=1 two-leg spin ladders. In the former case we discuss the (1/2)Ms plateau (Ms is the saturation magnetization), and for the latter case we discuss the (1/4)Ms and (3/4)Ms plateaux. We use the degenerate perturbation theory from the strong rung coupling limit and also the numerical diagonalization for finite systems.
Specific heat of an S=1 Quasi-1D Bond Alternating Antiferromagnet in a Magnetic Field
Masayuki Hagiwaraa, Naoyuki Tateiwab, Hiroko Aruga-Katoria, Tatsuo C. Kobayashic
aRIKEN (The Institute of Physical and Chemical Research), Wako, Saitama 351-0198, Japan
bGraduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan
cKYOKUGEN, Osaka University, Toyonaka, Osaka 560-8531, Japan
Long-range-ordering (LRO) hardly occurs in Quasi-1D antiferromagnets with an excitation energy gap at zero magnetic field. But, when the energy gap closes by application of magnetic field (Hc), we expect LRO at low temperatures. In this presentation, we will report the results of specific heat measurements on the S=1 quasi-1D bond alternating antiferromagnet Ni(C9H24N4)NO2(ClO4) in a magnetic field. We observed a sharp peak in the specific heat above Hc at low temperatures and will discuss the field-temperature phase diagram of the peak.
ESR Study of (C5H12N)2CuBr4*
S. Zvyagina, B. C. Watsonb, Ju-Hyun Parkb, D.A. Jensenc, A. Angerhoferc, L.-C. Brunela,
D.R. Talhamc, M.W. Meiselb
aNational High Magnetic Field Laboratory (NHMFL), Florida State University, Tallahassee 32310, USA.
bDepartment of Physics and NHMFL, University of Florida, Gainesville, FL 32611-8440, USA.
cDepartment of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA.
The title material1 has been indentified as an S=1/2 Heisenberg two-leg ladder.2 ESR studies at 9, 96, and 289 GHz have been made down to 4 K. The high frequency data resolve the two inequivalent magnetic sites reported by Patyal et al. and indicate the presence of a spin-singlet ground state. These data and their possible interpretation will be presented.
1 B.R. Patyal et al., PRB 41 (1990) 1657. 2 B.C. Watson et al., PRL 86 (2001) 5168.
*Supported, in part, by NSF DMR-0084173 for the NHMFL and ACS-PRF 36163-AC5.
The Substitution Effect of Co on the Electrical Resistivity of Sr14Cu24O41
Hiroshi Yoshimitsu, Masahiko Hiroi, Masayuki Kawakami
Department of Physics, Kagoshima University, Kagoshima 890-0065, Japan
We study the effect of substitution of Co for Cu on the electrical resistivity in two-legged ladder compound,
Sr14Cu24-xCoxO41.
We make single phase samples with Co concentration up to x=5 by usual solid state reaction. The electrical resistivity of Sr14Cu24-xCoxO41 for all x shows semiconductive behavior. It is found, however, that for Co concentration with x=4,5 the resistivity is much smaller than that for x=0. The effect of Co substitution with x=5 on resistivity is almost equal to that of Ca substitution for Sr with y=6 in Sr14-yCayCu24O41. Magnetic susceptibility measurements are also reported. The results are compared and discussed with the cases for Ca substitution.
Bond Spin-Density-Wave Phase in the Staggered Magnetic Field
Hiromi Otsuka
Department of Physics, Tokyo Metropolitan University, Tokyo 192-0397, Japan
We discuss a stability of the bond spin-density-wave (bond-SDW) phase observed in the one-dimensional (1D) interacting electron systems against the staggered magnetic field; a renormalization group (RG) analysis to the effective Hamiltonian implies that, due to the charge distribution in bond-SDW, the Néel correlation becomes short-range and the staggered magnetic field is irrelevant to the spin liquid part. As a result, the phase may survive in the weak field region. To realize bond-SDW and further to demonstrate its stability under the staggered magnetic field, we employ the 1D half-filled anisotropic extended Hubbard model; a numerical procedure to determine a stable region which is based upon the level-spectroscopy method is explained and used to confirm our RG argument.
ESR Study of Sine-Gordon Excitations in S=1/2 Antiferromagnetic Chain: Copper Benzoate
Takayuki Asanoa, Hiroyuki Nojirib, Yuji Inagakia, Takuo Sakonb, Jean-Paul Boucherc, Yoshitami Ajiroa, Mitsuhiro Motokawab
aDepartment of Physics, Kyushu University, Fukuoka 812-8581, Japan
bInstitute for Materials Research, Tohoku University, Sendai 980-8577, Japan
cLaboratoire de Spectrometrie, Universite J. Fourier, BP 87, F-38402 Saint-Martin d'Heres Cedex, France
We have observed directly sine-Gordon (SG) excitations and nonlinear energy gap (Eg(H)) in a very wide-field (H) and -temperature ranges up to 30 T and down to 0.5 K in Copper benzoate, Cu(C6H5COO)2·3H2O, which is one of the best representatives of S=1/2 antiferromagnetic Heisenberg quantum chain with staggered fields. A dynamical crossover between the gapless spinon regime and the gapped SG regime is revealed by means of electron spin resonance (ESR).
Theory of the Verwey Transition in Fe3O4
Hitoshi Seoa,b, Masao Ogatac, Hidetoshi Fukuyamad
aCorrelated Electron Research Center (CERC), AIST, Tsukuba 305-8562, Japan
bDomestic Research Fellow, Japan Science and Techonology Corporation, Kawaguchi 332-0012, Japan
cDepartment of Physics, University of Tokyo, Tokyo 113-0033, Japan
dInstitute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan
The metal-insulator transition in magnetite Fe3O4, the so-called Verwey transition, is re-investigated theoretically. We propose a scenario other than charge ordering, which has been considered to be its origin so far. We find that the orbital order in the t2g orbitals can make the system effectively one-dimensional, so that the bond dimerization is induced due to the Peierls instability. Based on considerations of the elastic energy in the presence of such bond dimer, we claim that a complicated three dimensional pattern of bond dimer is realized in the actual compound. Reference: Phys. Rev. B 65 085107, (2002).
Simultaneous Study of Local Magnetization and Resistivity in Phase Separated Manganites
Masashi Tokunaga, Yusuke Tokunaga, Tsuyoshi Tamegai
Dept. of Appl. Phys., Univ. of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
Phase separation (PS) phenomena have been widely recognized in many transition metal oxides. In manganites with perovskite-type structure, the PS into ferromagnetic metal and antiferromagnetic (or paramagnetic) insulator can be one of the origins to cause insulator to metal transition in a percolative way. Although there have been many studies that visualize the co-existing domains, little attempts have been reported to clarify the direct relationship with their transport properties. In this study, we utilized magneto-optical imaging technique to observe ferromagnetic domains in crystals of phase-separated perovskite manganites over the whole sample surface, and studied transport properties on the same sample over wide range of temperature and magnetic field.
Mott transition in Hubbard model compound FeSi
N.E. Sluchankoa, V.V. Glushkova, S.V. Demisheva, H. Ohtab, V. Moshchalkovc
aGeneral Physics Institute of RAS, Vavilov str., 38, Moscow, 119991, Russia
bKobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
cLaboratory Vaste-Stoffysica en Magnetisme, KULeuven, B-3001 Leuven, Belgium
Following to the study of transport and magnetization in steady magnetic field2 the galvanomagnetic properties of the narrow-gap semiconductor FeSi have been measured in pulsed magnetic fields up to 50T. It is shown that the Mott-Hubbard scenario of metal-insulator transition (MIT) with on-site Coulomb interaction U » 3D (D-is the band half-width) provides the most adequate description of the low temperature anomalies in this model system. The pulsed field transport anomalies can be also interpreted in terms of the MIT in magnetic field from a regime of a strongly correlated metal to insulating state.
The 51V-NMR study of Vanadium Hollandite
Takeshi Wakia, Harukazu Katob, Yuuko Morimotoa, Masaki Katoa, Kazuyoshi Yoshimuraa
aDepartment of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
bAdvanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan
Several vanadium compounds AxV8O16 are known to belong to the Hollandite family. We have investigated the temperature variations of the resistivity and magnetic susceptibility for some of them (A=Bi, Ba, Pb), which show non-stoichiometry in x composition (1.6 < x < 1.8 for Bi, 1.35 < x < 1.8 for Pb and x=1.1 for Ba), resulting in a wide variety of their physical properties depending on x. For example, Bi-Hollandites with 1.6 < x < 1.71 are metallic whole temperature range, while those with 1.72 < x < 1.8 exhibit a temperature-induced metal-insulator transition. In order to reveal their microscopic electronic states we have further performed 51V-NMR experiments and will report their results.
High-Frequency Dielectric Anomaly with Metal-Insulator Transition in CuIr2S4
Masuo Yamamotoa, Satoru Noguchia, Hiroki Ishibashib
aGraduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan
bDepartment of Materials Science, Osaka Prefecture University, Sakai 599-8531, Japan
CuIr2S4 has attracted much attention in the mechanism of the metal-insulator (MI) transition at 230 K, especially related to the charge-ordering (CO) state of Ir3+ and Ir4+. In the paper, we report the electromagnetic response of CuIr2S4 at 34 GHz measured by a cavity perturbation method. Temperature dependence of both the resonance frequency and the full width at half-maximum (FWHM) of Q-curves shows the anomalies around 230 K; a large shift in the resonance frequency from metal to insulator phase and a broad peak in the FWHM. The frequency shift is opposite sense to a usual MI transition. This behavior is similar to the case of the typical CO compound Pr0.5Ca0.5MnO3-d, which implies that the CO is accompanied with the MI transition of CuIr2S4.
Mott Transition in the multi-band Hubbard model in infinite dimensions
Yoshiaki Onoa, Ralf Bullab, Michael Potthoffc
aDepartment of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
bTheoretische Physik III, Institut für Physik, Universität Augsburg, D-86135 Augsburg, Germany
cInstitut für Physik, Humboldt-Universität zu Berlin, D-10115 Berlin, Germany
The Mott metal-insulator transition in the multi-band Hubbard model in infinite dimensions is studied by using the linearized dynamical mean-field theory. The critical interaction for the metal-insulator transition is obtained analytically. For the symmetric case with the orbital degeneracy M, the critical value is found to be given by Uc=(4M+2)Ö{L2}, where L2 is the second moment of the non-interacting density of states. We also derive an analytic expression for the discontinuity in the chemical potential in the change from hole to electron doping, for U larger than the critical value Uc. The results are in good agreement with the numerical results obtained from the exact diagonalization method.
Electronic Heat Capacity of CuIr2Se4 at Low Temperature
Shoichi Nagataa, Nobuhiro Matsumotoa, Ryo Endoha, Nobuo Wadab
a Department of Materials Science and Engineering, Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran, Hokkaido, 050-8585 Japan
bDepartment of Physics, Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
The normal thiospinel CuIr2S4 exhibits a temperature-induced metal-insulator (M-I) transition around 226 K with structural transformation, showing hysteresis on heating and cooling. It is important to see the difference of divalent anion between S and Se. In contrast to CuIr2S4, CuIr2Se4 remains metallic down to 0.4 K without the M-I transition. Heat capacity of CuIr2Se4 has been measured over the temperature range 0.5 to 11 K. The fit of the heat capacity data to C=gT+bT3 is very good with g=6.68 mJ\thinspacemol-f.u.-1\thinspaceK-2 and b=4.09 mJ\thinspacemol-f.u.-1\thinspaceK-4, where gT is the electronic heat capacity.
Magnetoresistance of Submicron-diameter Magnetic Rings
Jun-Yu Oua, J. C. Wua, Lance Hornga, S. Y. Hsub
aDepartment of Physics, National Changhua University of Education, Changhua 500, Taiwan.
bDepartment of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan.
Magnetoresistance (MR) measurements on magnetic rings having submicron-diameter at various temperatures have been carried out. The magnetic ring devices were fabricated using a standard electron beam lithography through a lift-off process. Note that non-magnetic current/voltage leads were patched on the magnetic ring in order to avoid any magnetization inhomogeneities formed in the junctions. Temperature dependent hysteresis behaviors along with jumps on the MR curves are interpreted due to formation and annihilation of magnetic vortex in the rings.
Itinerant electron ferromagnetism of FexCo1-xSi (x=0.3, 0.4, 0.5, 0.7) under high pressure
Katsuya Miuraa, Mamoru Ishizukaa, Takeshi Kanomatab, Hironori Nishiharac, Shoichi Endoa, Fumihisa Onod
aResearch Center for Materials Science at Extreme Conditions, Osaka University, Toyonaka, Osaka, 560-8531, Japan
bDepartment of Applied Physics, Tohoku Gakuin University, Tagajo, Miyagi, 985-8537, Japan
cFaculty of Science and Technology, Ryukoku Universitiy, Seta 1, Otsu , Shiga, 520-2194, Japan
dDepartment of Physics, Okayama University, Tsushima-naka, Okayama, 700-8530, Japan
The intermetallic compound FexCo1-xSi shows a weak itinerant ferromagnetism in the Fe concentration range of 0.2 < x < 0.95. We measured ac susceptibility for FexCo1-xSi (x=0.3, 0.4, 0.5, 0.7) under various pressures. We found that TC decreases in direct proportion with p3/4 with increasing pressure.
The Non-linear Susceptibility at Metamagnetic Transition in TbNiSn
Makoto Taki, Yoshiyuki Yamamoto, Hidenobu Hori
School of Materials Science, JAIST, 1-1 Asahidai Tatsunokuchi, Ishikawa 923-1292, Japan
The single crystal of TbNiSn is characterized by the four successive magnetic phase transitions at TN = 18.5 K, T3 = 7.6 K, T2 = 6.0 K, T1 = 2.2 K and the four multistep metamagnetic transitions along the easy axis(b-axis): critical field of Hc1 = 0.6 T, Hc2 = 1.5 T, Hc3 = 4.3 T, Hc4 = 5.3 T at 1.5 K. In addition to this TbNiSn single crystal shows a giant magnetoresistance(GMR) phenomenon near the critical fields of metamagnetic transitions. In order to clarify the origin of the GMR in this compound, we have performed the linear and non-linear AC-susceptibility of TbNiSn single crystals for b-axis in magnetic field up to 6 T at 4.2 and 1.8 K. The divergence of third higher-harmonic susceptibility was observed at Hc4 and Hc3 at 4.2 and 1.8 K, respectively. This suggests the spin relaxation time extremely increase around the crtical field.
Magnetic Structure of Rare Earth Metal Polytellurides Designed by Carrier Doping
Kazuya Suzuki, Teppei Okumura, Yuji Iyeiri, Takeshi Ohsawa
Graduate School of Environment and Information Sciences, Yokohama National University, Yokohama 240-8501, Japan
We report the magnetic structures of rare earth metal polytellurides designed by carrier doping. RTe3 consists of alternate stacking of one RTe layer and two Te layers. The ordered magnetic moment of RTe3 lies within the layer, in contrast to that of RTe2 having alternate stacking of one RTe and one Te layer where the magnetic moment is in the layer-stacking direction although the symmetry at the R atoms is the same. The difference originates from the effective charge in the Te layer. In R2Te5 consisting of the layer composite of the RTe2 and RTe3 unit, the magnetic ordering independently occurs in each unit and their ordered magnetic moments make an angle of nearly 90 degrees due to strong single ion anisotropy.
Hyperfine-Enhanced Nuclear Spin Order of PrPb3
Haruhiko Suzuki, Ayumi Ryu, Seiji Asada, Shumsun Nahaer, Satoshi Abe, Koichi Matsumoto, Tetsuo Kitai
Department of Physics, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan
The cubic compound PrPb3 with the AuCu3-type structure is known to undergo an antiferroquadrupolar phase transition at 0.4K. The ground state of the trivalent Pr ion in a cubic local symmetry is a nonmagnetic doublet G3. This G3 doublet splits into two singlet below 0.4K. We can expect that the hyperfine-enhanced nuclear moment will be differnet among the adjacent sites. We will report the hyperfine-enhanced nuclear spin order in an antiferroquadrupolar PrPb3, which can be expected at about 1mK.
Effect of Hund coupling in one-dimensional spin-orbital system
Hyun Leea, Hyun Leea, Patrick Azariab, Eduardo Boulatb
aDepartment of Physics, Sung Kyun Kwan University, Suwon, 440-746, South Korea
b Laboratorie de Physique Théorique des Liquides, Université Pierre et Marie Curie, 75252 Paris, France
The 1D spin-orbital model perturbed by Hund coupling is studied by renormalization group and bosonization methods. The Hund coupling breaks the SU(4) spin-orbital symmetry into SU(2)s×U(1)o at weak coupling fixed point. The one-loop renormalization group analysis shows that the Hund coupling is relevant irrespective of Coulomb repulsion. When Coulomb repulsion is larger than Hund coupling, the spin-orbital physics in strong coupling regime is described by SO(6) Gross-Neveu model, where the spin and orbital excitations are gapped. When the Hund coupling is much larger than the Coulomb repulsion, the strong coupling regime is described by the two coupled SO(3)s×SO(3)o GN model with the gapped excitations.
Possible Form of Multi-polar Interaction in Cubic Lattice
Osamu Sakaia, Ryousuke Shiinaa, Hiroyuki Shibab
aDepartment of Physics, Tokyo Metropolitan University, Tokyo 192-0397, Japan
bDepartment of Physics, Kobe University, Kobe 657-8501, Japan
Possible form of the interaction between multi-poles, including the octupole, is studied for the three types of the cubic lattice: simple cubic, body centered and face centered lattices. It is pointed out that coupling terms can be arranged in a way similar to that of the hopping matrix between the atomic orbitals. A table for s. c. lattice by Shiina et. al. (J. Phsy. Soc. Jpn. 67 (1998) 941) is generalized for the general wave number case of the three types of lattice. Recent experimental result of TmTe is analyzed. The development of the ferromagnetic component at the anti-ferromagnetic transition under the anti-ferro type quadrupolar order phase is discussed in a general point.
Canted Order in Nuclear and Electronic Magnetism of Pr Compounds
Yasushi Kinoshita, Machiko Nishino, Hiroumi Ishii
Graduate School of Science, Osaka City University, Osaka 558-8585, Japan
Canted magnetic arrangements can appear when there is no center of inversion between two magnetic ions. In such a crystalline field with low symmetry, a singlet ground state is realized for Pr ions. Two typical examples are studied. The first is PrCu6 studied by T. Hata et al., in which the electronic state remains paramagnetic and for the nuclear spins the Dzyaloshinsky-Moriya interaction is induced in the RKKY interaction3. The second is PrPtAl studied by H. Kitazawa et al. in which the canted magnetic order is induced in the electronic state. This is due to the single ion anisotropy energy whose principal axes differ each other at the two sites in the unit cell.
Magnetic Phase Transition in PdxCoO2
Hirotaka Okabea, Masanori Matobaa, Mitsuru Itohb
aDepartment of Applied Physics and Physico-Informatics, Keio Univerity, 3-14-1 Hiyoshi, Yokohama 223-8522, Japan
bMaterials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama 226-8503, Japan
PdCoO2 has a delafossite structure (space group R[`3]m) with alternative triangular layers of Pd, O, and Co. The Pd deficient compounds PdxCoO2(x=0.65, 0.43) were prepared by the cation exchange reaction. Their magnetic susceptibility mesurements were carried out in the temperature range between 4.2K and 300K, and it was found that Pd0.65CoO2 has antiferromagnetic ordering with a weak ferromagnetism at 50K. Specific heat mesurements for Pd0.65CoO2 and Pd0.43CoO2 showed the l-type anomaly at 50 and 30K, respectively, which is in good agreement with the magnetic susceptibility mesurements.
Elastic Constants of Antiferro-quadrupole Ordering System DyB2C2
Yuichi Nemotoa, Tatsuya Yanagisawaa, Koichiro Hyodoa, Terutaka Gotoa, Shingo Miyatab, Ryuta Watanukib, Kazuya Suzukib
aGraduate School of Science and Technology, Niigata University, Niigata 950-2181, Japan
bGraduate School of Engineering, Yokohama National University, Yokohama 240-8501, Japan
In order to investigate antiferro-quadrupole ordering in tetragonal system DyB2C2, we have measured elastic constants by ultrasonic method. Characteristic softenings of the C44 and (C11-C12)/2 corresponding to transverse modes were observed towards the transition temperature TQ=24.7 K. We propose that the CEF ground state is a pseudo quartet consisting of E1/2 doublet and E3/2 doublet in C4h site symmetry of Dy3+ ion, which is consistent with the present results of the elastic constants and specific heat. The magnetic field dependence of C44 and phase diagram obtained by the present study are also discussed.
Electrical and Magnetic properties of CeGa Single Crystal
Sadayoshi Koiwai, Masashi Kosaka, Nobuo Môri
Department of physics, Saitama University, Saitama 338-8570, Japan
We report on the study of the electrical and magnetic properties of CeGa with orthorhombic structure. The heat capacity has been measured in the temperature range between 0.4 K and 20 K under magnetic field up to 9 T. A sharp peak and a shoulder-like anomaly in the temperature dependent heat capacity are observed at 5.7 K and near 1 K, respectively. The sharp peak is due to the antiferromagnetic ordering transition, but the cause of the shoulder is unknown. As the magnetic field increases, the peak fades out and vanishes at about 4.2 T. The temperature of the shoulder-like anomaly is almost independent of magnetic field up to 3.5 T, but it rises suddenly above 3.5 T, crossing over TN at about 4.2 T.
The Magnetic Properties of Hypothetic Compounds RFe5 (R=rare earth)
Hiroyuki Nagai, Yasushi Amako, Shingo Kawakami, Takayuki Ishii, Hiroshi Yoshie
Department of Physics, Faculty of Science, Shinshu University, Matsumoto, Japan
The intermetallic compound RFe5, generally, cannot be prepared by common method . But we can estimate the magnetic properties of RFe5 by extrapolating x to 1 in R(Ni1-xFex)5 . The compounds of R=Y, Gd, Tb, Dy and Ho have been investigated. These compounds crystallize in the hexagonal CaCu5-type in the concentration range of x<0.5. In the case of R=Gd the metamagnetic behavior was observed for x>0.2, while other compounds of R=Y, Tb, Dy and Ho showed ferrimagnetic properties. The saturation magnetization of R=Tb, Dy and Ho decreased linearly with Fe concentration. The magnetic moments of Fe atoms were obtained by Mössbauer effect.
Magnetic Phase Diagram of GdGa1.75Al0.25
Tatsuichi Hamasakia, Hiroyuki Deguchib
aPhysics Department, Kyushu Sangyo University, Fukuoka 813-8503, Japan
bDepartment of Electronics, Kyushu Institute of Technology, Kitakyushu 804-8550, Japan
DC and AC magnetization of GdGa1.75Al0.25 have been measured in the magnetic field less than 5 tesla on polycrystalline material. In zero magnetic field, we have measured a specific heat and observed an antiferromagnetic transition at TN=24.0 K. A second transition has been observed at 22.9 K, immediately below TN. This transition has not been observed clearly by DC or AC magnetization measurement. A third transition has been observed at 7.7 K only by DC and AC magnetization measurements, which may be due to the change of the easy axis. Every temperature below TN we have observed metamagnetic transitions and obtained complex H-T phase diagram. With the exception of higher third transition temperature, the magnetic structure of GdGa1.75Al0.25 is similar to that of GdGa2.
De Haas-van Alphen Effect in GdAl3
Genfu Chen, Takenori Hayakawa, Shigeo Ohara, Isao Sakamoto
Department of Electrical and Computer Engineering, Nagoya Institute of Technology, Nagoya, Japan
The light rare earth trialuminide compounds RAl3 (R: La-Gd), crystallized in the hexagonal Ni3Sn-type structure, show a variety of physical phenomena. The role of 4f electrons in determining the physical characteristics is still under investigation. Among the RAl3 compounds, GdAl3 is a simple model material with Gd3+ ion in the 8S7/2 ground state, having no influence of crystal-field and Kondo effect. To clarify the Fermiology of GdAl3 we have measured de Haas-van Alphen (dHvA) effect at temperature down to 0.3 K up to 14 T. Many kinds of dHvA branches are detected and the dHvA frequencies range from 160 T to 2300 T. The largest frequency has the cyclotron effective mass 0.72 m0 along the [0001] direction. We have also investigated the anisotropies of electrical resistivity, Hall coefficient and thermopower in the temperature range 2 - 300 K.
On the ferromagnetism of high-spin states
Nadejda V. Terekhinaa, Rogdai Zaitsevb
aNIIteplopribor, Prospect Mira 95, Moscow 129085, Russia
b Russian Research Center, Kurchatov Institite, Kurchatov Sq1, 123 182 Moscow, Russia
The possibility of ferromagnetic ordering in a generalized Hubbard model and for infinite Hubbard energy is studied. The phase diagram of the ferromagnetism existence as a function of the degree of filling of d-shall is constructed. The calculation of the points of critical densities, between which ferromagnetic instability arises, was performed in a model of semielliptic primer density of state. On the bases of the deduced criterion, ferromagnetic instability was observed inside each integer interval of variation of the d-electron density. The appearance of separate regions of ferromagnetic instability is due to the possibility of change of sign of the scattering amplitude for Fermi excitations with opposite spin projections.
Magnetic susceptibility of substances at small Hubbard energy.
Julia V. Mikhailova
NII Teplopribor, Prospect Mira 95, Moskow 129 085, Russia
The estimation for shift of levels of a N-partial spectrum is received at small Hubbard energy. The correction to free state is obtained by perturbation method as: DEn = U (Smax2-Sn2)/N, where N - number of particles in system, Smax- of the greatest possible spin of system, Sn- total spin of system N- of particles for n-th state. For this purpose the size was calculated Dn= á Yn ,[^H]int Yn ñ / á Yn, Yn ñ, where [^H]int=U åi (ni ni ¯) is Hubbard interaction, Yn - wave function of n-th state. At calculations it was used, that the Hamiltonian [^H]0+[^H]int commutats with the operator of a total squared spin ([^S])2 of system. The account of thermodynamic and magnetic sizes with use of the received result is essentially determined by a type of a lattice.
Half-metallic ferromagnet of MnBi in zinc-blende phase
Ya-Qiong Xu, Bang-Gui Liu
Institute of Physics & Center of Condensed Matters Physics, Chinese Academy of Sciences, P O Box 603, Beijing 100080, China
Full-potential linear augmented plane wave method in density-functional theory was used to predict that MnBi in zinc-blende phase is a half-metallic ferromagnet with magnetic moment 4.000 mB per formula. This phase is robust against volume changes up to +20% and -12% and remains qualitatively the same under various approximations. Although this phase is meta-stable, it can be realized as thin films or nanostructures through epitaxial growth on right substrates with the same crystalline structure and appropriate crystal constants. This comes as a new member in the family of the several half-metallic ferromagnets, and may be useful in spintronics and other applications.
ESR Study on Metamagnetic Transition in CsFeCl3 up to 40 T
Meiro Chibaa, Tomoyuki Higuchib, Kiyofumi Kitaib, Seitaro Mitsudob, Toshitaka Ideharab,
Mitsuru Todac, Shizumasa Uedad
aDepartment of Applied Physics, Fukui University, Fukui 910-8507, Japan
bResearch Center for Development of Far Infrared Region, Fukui University, Fukui 910-8507, Japan
cInstitute of Materials Structure Science, KEK, Tsukuba 305-0801, Japan
dInstitute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011, Japan
In the S=1 fictitious spin system CsFeCl3 an anomalous magnetization has been observed under the magnetic field around 34 T, being much higher than the saturation field. It can not be explained in terms of the fictitious spin S = 1. In order to clarify the nature of the metamagnetic transition, an ESR experiment was performed under magnetic fields up to 40 T. The mechanism of the metamagnetic transition is discussed under the basis of the ESR frequency-field diagram.
Field effect on itinerant electron magnetism of Y1-xErxCo2 compounds
Takao Nakamaa, Masafumi Tokumuraa, Kiyoharu Uchimaa, Masato Hedob, Yoshiya Uwatokob, Katsuma Yagasakia, Haruo Nikia, Alexandre T. Burkovc
aFaculty of Science, University of the Ryukyus, Okinawa 903-0213, Japan
bISSP, University of Tokyo, Kasiwanoha 277-8581, Chiba, Japan
cA. F. Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg 194021, Russia
Thermopower S and electrical resistivity r of cubic Laves phase pseudo-binary compounds Y1-xErxCo2 were measured from 2 K to 300 K in magnetic fields up to m0H=15 T. S and r show a strong field dependence in a vicinity of the magnetic ordering temperature. The reduction of the exchage magnetic field Bexc acting on Co 3d electrons by Y substitution for Er results in a separation of magnetic transition temperatures of Er and Co subsystems in Y0.4Er0.6Co2. The collapse of the itinerant Co 3d moments of Y0.4Er0.6Co2 is induced by applying external magnetic field about 10 T.
11B NMR Study in the Tetragonal CeB2C2 Compound
Ko-ichi Magishia, Kuniyuki Koyamaa, Takahito Saitoa, Kiyoshi Mizunoa, Ryuta Watanukib, Kazuya Suzukib
aFaculty of Integrated Arts and Sciences, The University of Tokushima, Tokushima 770-8502, Japan
bGraduate School of Engineering, Yokohama National University, Yokohama 240-8501, Japan
It is known that CeB2C2 undergoes magnetic transitions to the antiferro-magnetic (AFM) phases at TN1 = 7.1 K and TN2 = 6.5 K. The purpose of this study is to clarify the magnetic properties and the magnetic structures in the AFM phases of CeB2C2 compound by means of 11B NMR measurement on a single crystalline sample. In the paramagnetic state, the NMR spectrum consists of a sharp peak with satellite lines. On the other hand, in the AFM phase, the spectrum was broadened and splitted into many resonance peaks by the internal magnetic field at B sites. The more detailed experiments and analyses are now in progress. We will report those results at the presentation.
Pressure tuning of the exchange interactions between s-electrons in a b.c.c. lattice of sodalite cages
Kenji Mizoguchia, Tsuneaki Yamabea, Hirokazu Sakamotoa, Ljiljana Damjanovicb, Vojislav I. Srdanovb
aDepartment of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan
bDepartment of Chemistry, University of California, Santa Barbara, CA 93106, USA
Néel and Weiss temperatures of the alkali-electro-sodalites (AES) loaded with Na or K were investigated as a function of hydrostatic pressure up to 2 GPa with a low-frequency ESR technique. The Néel temperature depends weakly, but the Weiss temperature decreases more sensitively with pressure. These pressure dependence could be well accounted for with a two-sublattice molecular field approximation. The assumption that the pressure causes a exponential decay of the transfer energies via the two-kinds of coupling windows, Hexagons and squares, is successful to reproduce the observed pressure dependence and to interpret systematically the ionic dependence with chemical pressure of 4-4.5 GPa for Na-ES.
Zeeman-like degeneracy of the massive ferromagnetic spin-wave mode
Paulo F. Farinasa, Kevin S. Bedellb
aCCET, Universidade S~ ao Francisco, Itatiba, SP 13251-900, Brazil
bDepartment of Physics, Boston College, Chestnut Hill, Massachusetts 02167
Hydrodynamic equations for an isotropic ferromagnetic state are derived from equations of motion. General conditions for the existence of additional collective modes (besides the known spin-waves) are stated. It is found that a recently derived massive mode carries a degeneracy with respect to chiral symmetry that may be helpful in experiments aiming to observe such a new mode.
Critical Phenomena in Double-Exchange Systems
Yukitoshi Motomea, Nobuo Furukawab
aERATO-SSS, JST, Tsukuba, Ibaraki 305-8562, Japan
bDepartment of Physics, Aoyama Gakuin University, Setagaya, Tokyo 157-8572, Japan
Critical phenomena of metallic-ferromagnetic transition are studied in double-exchange systems. A recently-developed Monte Carlo method is applied to obtain results in the thermodynamic limit through the finite-size scaling. Our results clearly show an importance of strong fluctuations in this itinerant system. The ferromagnetic transition belongs to the universality class with short-ranged interactions which is distinct from the mean-field one. The calculated critical temperature and exponents are quantitatively compared with experimental results in colossal magnetoresistance manganites. We also study phase diagram and critical phenomena in the competition between the double-exchange ferromagnetism and the superexchange antiferromagnetism. Randomness effects on this competition are discussed.
The angular dependent magnetoresistance in a-(BEDT-TTF)2KHg(SCN)4
Balázs Dóraa, Kazumi Makib, Mario Basleti\'cc, Bojana Korin-Hamzi\'cd
aDepartment of Physics, Technical University of Budapest, H-1521 Budapest, Hungary
bMax Planck Institute for Physics of Complex Systems, Nöthnitzer Str. 38, D-01187, Dresden, Germany
cDepartment of Physics, Faculty of Science, POB 331, HR-10001 Zagreb, Croatia
dInstitute of Physics, POB 304, HR-1001 Zagreb, Croatia
The nature of low temperature phase (LTP) of a-(ET)2 salts is still elusive in spite of intensitive study of the angular dependent magnetoresistance (ADMR) about a decade ago. Here we present a new study of ADMR of a-(ET)2 salts, assuming LTP is unconventional charge density wave (UCDW). In the presence of magnetic field the quasiparticle spectrum is quantized á la Landau. This gives rise to a striking ADMR in UCDW. The present model appears to account for salient aspects of many existing ADMR data of a-(ET)2KHg(SCH)4 remarkably well. This gives convincing support that LTP in a-(ET)2 salts is UCDW.
Sub-Nanometer Domain Wall Motion: Single Pinning Centre Coercivity
Kostya Novoselova, Andre Geima, Dirk van den Bergenb, Sergey Dubonosa, Jan Kees Maanb
aDepartment of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
bHigh Field Magnet Laboratory, University of Nijmegen, 6525ED, Nijmegen, The Netherlands
Nanometer-scale propagation of domain walls in garnet films has been studied by ballistic Hall micro-magnetometry. At low temperatures domain walls are found to move by nanometer-size jumps and each individual jump can be attributed to pinning on an individual defect. The jumps are reproducible for small changes of external magnetic field. At T above 5 K, the coercivity of a typical pinning center (i.e. magnetic field required to de-pin a domain wall) is found to be ~ 5 G and decrease with increasing temperature. This temperature dependence allows us to determine the characteristic energy and size of the pinning center. Unexpectedly, at T below 5 K the coercivity saturates and even shows a tendency to decrease. Possible explanations for this behavior will be discussed (nuclear spin diffusion, tunnelling).
Weak ferromagnetism, compensation point and temperature induced magnetization reversal in Ni(HCOO)2*2H2O
H. Kageyamaa, D.I. Khomskiib, R.Z. Levitinb, A.N. Vasilievc
aInstitute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
bUniversity of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
cPhysics Faculty, Moscow State University, 119992 Moscow, Russia
In Ni(HCOO)2*2H2O the transition into weak ferromagnetic state occurs at TN = 15.5 K. At lowering temperature an initial increase of magnetization gives way to a gradual decrease and the compensation point is observed at TC = 8.5 K. There are two nonequivalent positions in Ni subsystem, i.e. Ni1 and Ni2. The origin of weak ferromagnetic moment is due to the tilt of easy axes of magnetization in NiO6 octahedrons belonging to each subsystem. The appearance of compensation point is related to different temperature dependencies of Ni1 and Ni2 subsystem magnetizations.
Magnetic Properties of Weak Itinerant Electron Ferromagnet Ni-Pt Alloy
Keiichi Koyamaa, Hiroe Sasakib, Takeshi Kanomatab, Kazuo Watanabea, Mitsuhiro Motokawaa
aInstitute for Materials Research, Tohoku University, Sendai 980-8577, Japan
bFaculty of Engineering, Tohoku Gakuin University, Tagajo 985-8537, Japan
Precise magnetization measurement and high field magnetization measurement have been performed for Ni-Pt alloy in magnetic fields up to 10 kOe using a SQUID magnetometer and in magnetic fields up to 130 kOe using a VSM magnetometer, respectively, in temperature range from 5 K to 280 K. The spontaneous magnetization MS(T) follows a (1 -(T/TC)2)-dependence below 15 K. In the temperature range from 15 K to Curie temperature (42 K), however, MS(T) decreases with the proportional to (1-(T/TC)4 / 3). Obtained results can be explained with a new spin fluctuation theory of Takahashi.
Field-Induced Ferromagnetic Transition in PrInNi4
N. Tsujii, H. Kitazawa, H. Suzuki, M. Imai, G. Kido
National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
We report on the magnetic properties of a new ternary compound PrInNi4. PrInNi4 has the cubic MgSnCu4-type structure. Magnetization M and electrical resistivity r as functions of temperature T for magnetic field H £ 0.5 T reveal that magnetic ordering is absent above 2 K, and the ground state is a nonmagnetic crystal field level. For H ³ 0.7T, M and r vs. T show a sharp jump at T @ 3 K. Below this temperature, M saturates around 1.5-2 mB. These facts indicates that PrInNi4 undergoes a ferromagnetic transition at Tc @ 3 K for applied field H ³ 0.7 T. The sharp jump suggests that hybridization of the wave function of the crystal field levels occurs rapidly around Tc. M and r vs. H exhibit a nonmagnetic-ferromagnetic transition at Hc = 0.7 T for T = 2 K. This field-induced transition will be discussed in relation to the competition of the crystal field effect and the ferromagnetic exchange interaction.
Two-scale analysis of the Hubbard model
Adolfo Avella, Ferdinando Mancini, Sergey Krivenko
Dipartimento di Fisica ``E.R. Caianiello'' - Unità
INFM di Salerno
Università degli Studi di Salerno, I-84081 Baronissi (SA),Italy
A two-scale approach for an analysis of the Hubbard model has been developed. The dynamics has been obtained from equations of motion of fermionic composite operators, which were split in high and low frequency components. A fully self-consistent solution which exactly conserves the first spectral moments has been found. Some local and thermodynamics properties have been computed and compared fruitfully with numerical results available in literature.
Phase Separation in Magnetically Ordered Semimetals and Half-metals
Ikhiel Korenblit
School of Physics & Astronomy, R.& B. Sackler Faculty of Exact Sciences, Tel-Aviv University, Tel-Aviv 69978, Israel
We showed that in ferromagnetic semimetals, in which the RKKY indirect exchange predominates, as e.g., in EuB6, the magnetically ordered state at finite temperatures, T, is unstable against phase separation (PS) into regions with enhanced and suppressed ferromagnetic correlations. Considering the energy of the slightly inhomogeneous electron gas in the Hohenberg-Kohn approximation, we obtained the phase diagram in the (T,carrier concentration ), and in the (magnetic field, carrier concentration) planes. The results explain qualitatively the magnetic properties of EuB6. The same approach was used to investigate PS in the ground state of slightly doped double-exchange manganites. The scale of the PS regions is fixed by the Coulomb screening of the carriers, and it is of order of several lattice constants.
Studies of single crystal ErCo2 under pressure and magnetic field
Jaeyoung Wooa, Younghun Job, H.C. Kimc, A. Pirogovb, J.-G. Parkb
aDepartment of Physics, Inha University, Incheon 402-751, Korea
bDepartment of Physics and Institute of Basic Science, SungKyunKwan University, Suwon 440-746, Korea
cMaterial Science Laboratory, Korea Basic Science Institute, Taejeon 305-333, Korea
We investigated first order magnetic transition of ErCo2 at 35 K by measuring resistivity and magnetization under pressures (up to 12 kbar) and magnetic fields (18 Tesla) with a single crystal sample. With increasing pressure the ferromagnetic transition moves towards lower temperatures while it increases in temperature with magnetic fields. We note that the first order nature of the magnetic transition is suppressed by pressures or fields, and it is expected to become of second order type at above 60 kbar and 20 Tesla. We will discuss this pressure or field induced transition in the nature of the magnetic transition of ErCo2.
NMR Study of Two-Dimensional Ferromagnet K2CuF4
at Millikelvin Temperatures
Rui Goto, Keiichirou Nakamura, Kunihide Okada, Muneaki Fujii
Department of Physics, Kumamoto University, Kumamoto 860-8555, Japan
Two-dimensional ferromagnet K2CuF4 is an ideal compound in which to study two-dimensional magnetic systems because the interplane exchange coupling constant is much smaller than intraplane exchange coupling constant. We measured the temperature dependence of the NMR frequencies of the 1/2«3/2 transition for 63Cu and 65Cu nuclei in K2CuF4 single crystal. The NMR measurements were made by spin-echo method at zero applied magnetic field. The experimental results are discussed in the framework of the two-dimensional spin wave theory at very low temperatures.
Successive Magnetic Transitions and Multi-Step Magnetization in GdBC
Akinori Matsumoto, Akihiro Muramoto, Satoru Noguchi
Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan
GdBC crystallizes in the orthorhombic YBC-type structure. Antiferromagnetic-like transition temperature, TN = 45 K is inferred by the magnetic susceptibility, resistance and heat capacity measurements. Another magnetic transition may occur around Tm = 25 K, where the susceptibility shows a broad peak and the heat capacity shows a small anomaly. In the paper, we report the results of the magnetization measurements in GdBC single crystal by using a SQUID magnetometer up to 5 T and a pulsed-magnet system up to 30 T. The magnetization for H||b at 4.2 K shows three steps at 1, 5 and 15 T, being saturated above 23 T. The saturation moment is almost 7 mB/Gd. Temperature dependence of the step fields is obtained for all axes. These imply that GdBC has successive antiferromagnetic transitions with complex magnetic structures in spite of the simple spin system of Gd3+.
Magnetic phase diagram of Ce2Fe17 under high pressures in high magnetic fields
Fumihiro Ishikawaa, Tsuneaki Gotoa, Hironobu Fujiib
aInstitute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8581, Japan
bFaculty of Integrated Arts and Science, Hiroshima University, Higashi-Hiroshima 739-8521, Japan
Magnetization measurements were performed on Ce2Fe17 under high pressures up to 1.2 GPa and in magnetic fields up to 18 T. We determined the magnetic phase diagram in the B-T plane at 0, 0.3, 0.4, 0.6, 0.9 and 1.2 GPa. At 0 GPa, five magnetic phases exist and the application of high pressure produces two additional magnetic phases. The shape of the phase diagram changes drastically with increasing pressure. The appearance of the new magnetic phases is considered to be related to the competing exchange interactions among the Fe magnetic moments.
Effect of Berry's phase on the conduction electrons g factor in Zn
Yuri V. Sharlai, Grigorii P. Mikitik
B.Verkin Institute For Low Temperature Physics & Engineering, National Ukrainian Academy of Sciences, Kharkov 61103, Ukraine.
In metals the semiclassical quantization condition for energy levels of electrons in a magnetic field depends on Berry's phase. When the closed electron orbit in the magnetic field links to band-contacts lines, Berry's phase can be nonzero, and in this case even a small spin-orbit interaction leads to an essential difference of the conduction electron g factor from its free electron value, g=2. To clarify this point, we calculate and analyze the g factor for the three-band model of the electron spectrum which can describe the so-called needles in Zn. We show that in zinc Berry's phase effect on the electron g factor is comparable with the spin-orbit contribution to it. We discuss a way of extracting Berry's phase contribution to g factor from experimental data.
Conduction electron g factor in metals
Yuri V. Sharlai, Grigorii P. Mikitik
B.Verkin Institute For Low Temperature Physics & Engineering, National Ukrainian Academy of Sciences, Kharkov 61103, Ukraine.
We theoretically investigate the electron g factor which is experimentally determined from the de Haas-van Alphen effect. Although formulas for the g factor were first derived by Roth in 1966, they are sufficiently complicated and have not been used in practice so far. We represent the formulas in a more convenient form which also admits a simple physical interpretation. It follows from these formulas that numerous computations of the g factor performed earlier (using the local g factor method) did not take into complete account spin dynamics of a semiclassical Bloch electron moving in a magnetic field. This can lead to inaccurate results for the g factor if the spin-orbit interaction in a metal is not small. We also point out that the concept of local g factors is not generally correct for a strong spin-orbit coupling.
Magnetization and Ground State Spin Structures of Ising Spin System with Four-Spin Interaction
T. Iwashitaa, K. Uragamia, K. Gotoa, T. Idogakib
aCollege of General Education, Kyushu Tokai University, Kumamoto 862-8652,Japan
bDepartment of Applied Quantum Physics, Kyushu University, Fukuoka 812-8581, Japan
The magnetic properties of the spin S(=1/2 and 1) Ising systems with the bilinear exchange interaction J0SizSjz and the four-site four-spin interaction JSizSjzSkzSlz have been discussed by making use of the Monte Carlo simulation. At low temperature region, the magnetization curve has an inverse inclination and decreases with the decrease of temperature under a certain condition of the value J/J0. This anomalous behavior is considered to be originated in the non-ferromagnetic spin structures which have a little higher energy than the one of the ground state, and the relation between the value of the magnetization at zero-temperature and the spin structure expected for the ground state has been made clear.
Enhancement of the Kondo Effect in a mechanically deformed Cu(Mn) alloy
Masahito Nakagawa, Yasukage Oda
Department of Material Science, Graduate School and Faculty of Science, Himeji Institute of Technology, Ako-gun, Hyogo 678-1297, Japan
We have studied the Kondo effect in mechanically deformed Cu(Mn), through measurements of the temperature dependence of the resistivity. Both the logarithmic Kondo slope at low temperature and the temperature of maximum resistivity due to spin glass transition become a little larger than not deformed one. The origin of these phenomena seems to be enhancement of the Kondo effect due to increase of Mn atoms in the neighborhood of dislocations.
Magnetic Properties of Amorphous Mn100-xCex Alloys
Shinya Kikegawaa, Takuya Matsumuraa, Shigeyuki Murayamaa, Hideaki Takanoa, Yoshihisa Obib
aMuroran Institute of Technology, Muroran 050-8585, Japan
bInstitute for Materials Research, Tohoku University, Sendai 980-8577, Japan
The magnetic susceptibility and thermal expansion of amorphous(a-) Mn100-xCex alloys for 20 < x < 80 fabicated by DC-sputtering have been measured. The susceptibility shows a simple Curie-Weiss behavior except its insignificant defference in between ZFC and FC states at low temperature. The thermal expansion a for a-Mn100-xCex shows the Debey-type temperature dependence for 20 < x < 40, although the value is much larger than that for typical amorphous alloys. Furtermore, the a increases with increasing Ce concentration. On the other hand, a-Mn100-xCex for 50 < x < 80 shows that the a decreases with increasing Ce concentration in the high temperature side, and below 100K the a shows a large increase with decreasing temperature. This would be anomalous effect of 4f electrons in these alloys.
Metamagnetism of PrCu2X2(X=Si and Ge)
Toru Shigeokaa, Yasuyuki Tanedaa, Masato Hedob, Yoshiya Uwatokob
aFaculty of Science, Yamaguchi University, Yoshida, Yamaguchi 753-8512, Japan
bInstitute for Solid State Physics, University of Tokyo, Chiba 277-8581, Japan
Magnetic behavior at low temperature has been investigated on the single crystal compounds PrCu2X2(X=Si and Ge) which are reported to have anomalous high Neel temperatures. The compound PrCu2Si2 shows a very sharp one-step metamagnetic transition in the c-axis magnetization process at low temperature, whereas PrCu2Ge2 shows a four-step metamagnetic process in the initial ascending process. The descending process changes to a one-step one. The magnetization in the descending process decreases rapidly, crosses over one of the ascending process and reaches near zero; The process is irreversible and very peculiar, which has been never seen yet. The origin will be discussed from comparison of the both compounds.
Raman Scattering of RB6 (R=Ca, Ce, Dy, Gd, Pr and Yb)
Norio Ogitaa, Shinji Nagaia, Naoki Okamotoa, Masayuki Udagawaa, Fumihiko Igab, Masafumi Serab, Jun Akimitsuc, Satoru Kuniid
aFaculty of Integrated Arts & Sciences, Hiroshima University, Hiroshima 739-8521, Japan
bGraduate School of Advanced Sciences of Matter, Hiroshima University, Hiroshima 739-8526, Japan
cDepartment of Physics, Aoyama-Gakuin University, Tokyo 157-8521, Japan
dDepartment of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
In Raman scattering spectra of RB6, anomalous peaks have been found below 200cm-1 for the R+3B6, except for phonons and CEF excitations. Their peak intensities decrease with decreasing temperature and this temperature dependence correlates with that of the mean square displacement of R. Furthermore, their energies decrease with the increase of the cage size of B. This new excitation can be attributed to a local vibration of the R ion, which can be regarded as "rattler" in the cage of B.
Magneto-Volume Effect in the Ground and Field Induced States of Ce2Fe17
Yoshikazu Makiharaa, Hironobu Fujiib, Tetsuya Fujiwarab, Kazuo Watanabec, Kohki Takahashic, Keiichi Koyamac, Mitsuhiro Motokawac
aPhysics Department, Kyushu Kyoritsu University, Kitakyushu 807-8585, Japan
bFaculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739-8521, Japan
cInstitute for Materials Research, Tohoku University, Sendai 980-8577, Japan
X-ray diffraction measurements on Ce2Fe17 have been performed in the temperature range from 8 to 300K at the magnetic fields up to 5T. A clear spontaneous linear magnetostriction is observed in the c-axis below TN=210K in the antiferromagnet Ce2Fe17 with a helical spin structure in the ground state. On the other hand, no remarkable anomaly is observed in the a-axis at the magnetic transition temperature Tt=125K. It has been found that the structural phase transition occurs in the Ce2Fe17 simultaneously with the metamagnetic transition below Tt.
Ferromagnetism in Lanthanum Doped CaB6: Is it Intrinsic?
Takao Mori*, Shigeki Otani
Advanced Materials Laboratory, National Institute for Materials Science, Namiki 1-1, Tsukuba, 305-0044, Japan
The magnetism of flux grown single crystals of undoped and lanthanum doped Ca1-xLaxB6 was systematically investigated, taking especial care in the preparation and quality control of crystals. It is strongly indicated that the ferromagnetism (first reported in Nature by Young et. al.) originates from iron impurities rather than being an intrinsic effect of the lanthanum doping of CaB6.
Density Waves in the Organic Metal a-(BEDT-TTF)2KHg(SCN)4
Masaru Kato
Department of Mathematical Sciences, Osaka Prefecture University, Sakai, Osaka, 599-8531, Japan
We have investigated possible spin and charge density waves in the organic metal
a-(BEDT-TTF)2KHg(SCN)4.
This system shows density wave like transition at T=8 K, and the nature of
the density wave is not clarified up to now.
Using a realistic tight binding model 4
and an inhomogeneous mean-field theory,
we obtained several stable density wave states.
Especially, spin density wave states (SDW) are stable only for large on-site Coulomb
interaction U ³ 800 meV.
Their spin moments are tiny and inhomogeneous
even in the unit cell.
Also charge density waves (CDW) appear simultaneously with the SDW.
We also discuss results of the electron spin resonance experiment and the possibility of
CDW state.
Anomalous Behavior in Quadrupolar Ordering Temperature in Pr(Pb1-xSnx)3
Kenji Yuruea, Tatsuya Kawaea, Masaki Mitoa, Masako Hitakaa, Kazuyoshi Takedaa, Hiroumi Ishiib, Tetsuo Kitaic
aDepartment of Applied Quantum Physics, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan
bFaculty of Science, Osaka City University, Sugimoto, Osaka 558-8585, Japan
cFaculty of Engineering, Kyushu Institute of Technology, Kitakyushu 804-8585, Japan
Specific heat measurements has been carried out in Pr(Pb1-xSnx)3 (x=0, 0.03, 0.05, 0.1 and 0.2) with a non-Kramers G3 doublet in the crystal-electric-field ground state. The ordering temperatrure of the quadrupolar moments shows an anomalous behavior as Sn concentration increases. A sharp peak due to the quadrupolar ordering at TQ=0.4 K in x=0 is suppressed below 0.1 K only in x=0.03. Surprisingly, the peak turns to increase at x=0.05, and shifts to higher temperatures with the Sn concentration. At x=0.2, TQ is expected to be ~ 0.15 K. The possible origin of this behavior is discussed.
Dissimilar hysteresis of Ni films and its combined effect in Ni/Si/Ni/GaAs
Syed Anisul Haque, Akira Matsuo, Yoshiyuki Yamamoto, Hidenobu Hori
School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Tatsunokuchi, Nomi-gun, Ishikawa 923-1292, Japan
Dissimilar magnetization processes and coercive fields of Ni films were observed while it was separately deposited onto Si(001) and GaAs(001) substrates. By combining these two systems a multilayer of Ni/Si/Ni/GaAs is prepared. The magnetization process of this multilayer at different temperatures is observed. Because of the difference of the coercive field of Ni films, the spin reversal occurs in two phases. The Ni film on Si having low coercivity does it first, while the Ni film on GaAs does it later. This enables to achieve an antiferromagnetic spin state in the multilayer. The field range, for which the believed antiferromagnetic spin state remains, becomes larger as the temperature decreases and it almost disappears with the increase of temperature.
Magnetic Measurement of Rare Earth Ferromagnet Gadolinium Under High Pressure
Tomoharu Iwamoto, Masaki Mito, Masako Hidaka, Tatsuya Kawae, Kazuyoshi Takeda
Department of Applied Quantum Physics, Kyushu University, Fukuoka, 812-8581, Japan
Magnetic property of rare earth ferromagnet gadolinium(Gd:Tc = 293 K) has been observed under pressures up to 15 GPa, using a miniature diamond anvil cell (DAC) installed in a SQUID system. Pressurization suppresses both the ferromagnetic moment and the transition temperature with increasing pressure. The crystal structure keeps the same symmetry below 6 GPa. We have found that the ferromagnetic signal has disappeared. The results will be discussed on the exchange interaction among the isotropic 4f-metallic system.
Ferromagnetic ordering in doubly degenerate Hubbard model with correlated hopping
Leonid Didukha, Oleksandr Kramara, Yuriy Skorenkyya, Vasyl Hankevycha,b
aDepartment of Physics, Ternopil State Technical University, UA-46001 Ternopil, Ukraine
bInstitute for Theoretical Physics, University of Heidelberg, D-69120 Heidelberg, Germany
The ferromagnetic ordering stabilization in the ground state of the model which describes the intra-atomic Coulomb repulsion, inter- and intra-atomic exchange interactions and correlated hopping of electrons in a doubly orbitally degenerate band is studied. The ground state energy of the model is calculated. On this base the magnetization of system as well as ferromagnetism stabilization condition are found. The correlated hopping of electrons is shown to lead to a specific translational mechanism of the ferromagnetic ordering stabilization. The peculiarity of the obtained expressions is their concentration dependence, which can explain corresponding dependence experimentally observed in transition metal compounds.
Magnetism, Structure, and Superconductivity of Cd2Re2O7 Pyrochlore: Cd NMR and Re NQR.
O. Vyaselev, K. Arai, K. Kobayashi, J. Yamazaki, K. Kodama, M. Takigawa, M. Hanawa, Z. Hiroi
Institute for Solid State Physics, University of Tokyo 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
We report Cd NMR and Re NQR on Cd2Re2O7, the first and as yet the only superconductor among pyrochlore oxides (Tc @ 1 K). The Re NQR spectrum rules out any magnetic or charge order. Re spin-lattice relaxation rate below Tc exhibits a pronounced coherence peak and follows the weak-coupling BCS theory with nearly isotropic energy gap. The angular dependence of Cd spectrum reveals two structural phase transitions, one at 200 K and another at 120 K. Cd NMR results point to moderate ferromagnetic enhancement at high temperatures followed by rapid decrease of the density of states below 200 K, and to strong suppression of spin fluctuations below 120 K.
Ferromagnetism in Hubbard models with nearest-neighbor Coulomb repulsion
Hiromitsu Ueda, Akinori Tanaka, Toshihiro Idogaki
Department of Applied Quantum Physics, Kyushu University, Fukuoka 812-8581, Japan
We propose a mechanism which leads to ferromagnetism in extended Hubbard models on lattices composed of triangles. We show that the ferromagnetic ground state is stabilized in the quarter filling case through a third-order electron exchange process around a triangle when both the on-site repulsive interaction and the nearest-neighbor one are much larger than the hopping terms. Numerical calculations for a one-dimensinal lattice connected by triangles give the evidence that the ground state is ferromagnetic not only in the quarter-filling case but also away from quarter-filling.
This result indicates possibilities of ferromagnetism on some other kinds of one-, two- and three-dimesional lattices composed of triangles.
Resistivity and thermopower of CaB6 single crystal
Katsuma Yagasakia, Shiko Notsua, Yuko Shimojia, Rina Kajib, Tetsuya Yokoob, Jun Akimitsub, Masato Hedoc, Yoshiya Uwatokoc
aFaculty of Science, University of the Ryukyus, Okinawa 903-0213, Japan
bDepartment of Physics, Aoyama-Gakuin University, Chitosedai, Setagaya-ku, Tokyo 157-8572, Japan
cInstitute for Solid State Physics, University of Tokyo, Kashiwanoha, Chiba 277-8581, Japan
The resistivity r and thermopower S of CaB6 single crystal have been measured at temperatures from 2K to 1100K in magnetic field up to 15T. Temperature dependence of r is expressed as 1.7-th power of T for 120 K ³ T ³ 1100 K, where r0=232 mWcm. The magnitude of r is very large for metal and can be considered as semi metal. There are no anomalies in both of r and S above 400 K where it might be considered to have ferromagnetic transition. r and S can be fitted on the basis of free electron model by semi-metal with simple electronic pocket.
Anomalous magnetism in R2Mn3Si5 (R = Tb, Dy, Ho and Er) compounds
R Nirmalaa, V Sankaranarayanana, K Sethupathia, Y Yamamotob, H Horib, AV Morozkinc
aDept. of Physics, Indian Institute of Technology,Madras -600 036, India
bSchool of Material Science, Japan Advanced Institute of Science and Technology, Ishikawa, Japan
cDept. of Chemistry, Moscow Lomonosov State University, Moscow, Russia
As the rare earth intermetallic compounds with transition metal Mn has a special attraction by displaying anomalous magnetic character depending on the competition between R-Mn and Mn-Mn exchange interactions, new, polycrystalline, tetragonal Sc2Fe3Si5 - type R2Mn3Si5 (R = Tb, Dy, Ho and Er) compounds have been synthesized and characterized. Low temperature dc magnetization measurements revealed a paramagnetic to a ferromagnetic phase transition.The paramagnetic susceptibility follows Curie - Weiss law and Mn is found to carry magnetic moment in addition to rare earth. Saturation magnetization is not observed even at high fields of 7T.
Peculiarities of spin reorientation in a thin YIG film
Ya.B. Bazaliya, A.I. Linnikb, L.T. Tsymbalb, P.E. Wigenc
aArgonne National Laboratory, MSD, 9700 S. Cass Ave, Argonne, IL 60439, USA
bO.Galkin Donetsk Physics & Technology Institute, R.Luxemburg 72, Donetsk, 83114, Ukraine
cOhio State University, Physics Department, 174 W.18th Ave, Columbus, OH USA
The issue of magnetic orientation transitions in thin films combines interesting physics and importance for applications. We study magnetic transition and phase diagram of the 0.1mm thick (YLaGd)3(FeGa)5O12 films grown on the GGG substrate by liquid phase epitaxy. The nature of orientation transition is determined by demagnetizing fields, material parameters and orientation of the crystal structure relative to the film plane. It is contrasted with the one for BiGa:TmIG thin films, studied in previous work by one of the authors. The phase diagram is discussed in terms of magnetic energy that includes cubic magnetocrystalline, growth induced, and shape anisotropy energies.
Single Crystal Growth and Magnetic Susceptibility of Tm3Al5O12
Junji Awaka, Tokuichi Kurimoto, Shoichi Nagata
Department of Materials Science and Engineering, Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran, Hokkaido, 050-8585 Japan
The single crystals of garnet type Tm3Al5O12 have been successfully grown by a flux method. The susceptibility was measured with an rf-SQUID magnetometer over the temperature range of 2.0 to 300 K in a constant magnetic field of 10 kOe. Tm3+ ion has an even number of 12-electrons in the 4f shell, avoiding the Kramers doublets. The typical Van Vleck paramagetism has been manifestly observed. The detailed analysis will be presented on the basis of crystal field splitting.
Magnetism in NdPtSn
Blanka Janousováa, Vladimír Sechovskýa, Takemi Komatsubarab, Pavel Svobodaa
aDept. of Electronic Structures, Charles University, 121 16 Prague 2, Czech Republic
bDept. of Physics, Graduate School of Science, Tohoku Univ., Sendai 980-8578, Japan
NdPtSn, similarly to other RPtSn compounds (R = light rare earth), crystallizes in the orthorhombic TiNiSi-type structure with space group Pnma.
We present first results of magnetization and specific-heat measurements on a single crystal of this material at temperatures down to 0.5 K and in magnetic fields up to 9 T.
The Cp vs. T dependence reflects two magnetic phase transitions, namely at 2.4 K (second-order) and at 1.9 K (first-order). The temperature dependence of susceptibility shows a maximum at around 2.7 K. An S-shape develops on magnetization curves when decreasing temperature below 3 K.
A tentative magnetic phase diagram based on magnetic and specific-heat data and will be presented.
2D soliton-vortices in Heisenberg-Maxwell sigma model
Igor L. Bogolubskya, Alla A. Bogolubskayab
aLaboratory of Information Technologies, Joint Institute for Nuclear Research, 141980 Dubna, Moscow region, Russia
bLaboratory of Information Technologies, Joint Institute for Nuclear Research, 141980 Dubna, Moscow region, Russia
Stable string-like topological soliton analogues of Abrikosov-Nielsen-Olesen vortex defects in Ginzburg-Landau (abelian Higgs) theory are found within U(1) gauged extension of the easy-axis Heisenberg antiferromagnet model. Their energy does not exceed that of Belavin-Polyakov solitons in isotropic ferromagnet.
Fermi surfaces of YFe2 and YNi2
K. Nakadaa, H. Shimizub, H. Yamadab
aGraduate School of Science and Technology, Shinshu University, Matsumoto 390-8621, Japan
bFaculty of Science, Shinshu University, Matsumoto 390-8621, Japan
The FLAPW electronic structures and Fermi surfaces of YFe2 and YNi2 with a cubic Laves phase structure are calculated in the non-magnetic state. Calculated results of the density-of-states are compared with the previous ones. Angular dependence of the extremal cross-sectional areas of the Fermi surfaces of these compounds are also calculated.
MULTIPLE MAGNETIC TRANSITIONS IN Gd5Rh4Ge10 SINGLE CRYSTAL
S. Ramakrishnana, G. J. Nieuwenhuysb, J. A. Mydoshc
aTata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400 005, India
bKamerlingh Onnes Laboratory, University of Leiden, The Netherlands
cKamerlingh Onnes Laboratory, University of Leiden, The Netherlands
We report the observation of quadruple magnetic transitions in a single crystal of Gd5Rh4Ge10 at 14 K, 8.5 K, 7 K and 6 K via resistivity, susceptibility and heat-capacity studies. At least two of these transitions at 6 K and 7 K are completely suppressed in a field of 5 T applied along the c-axis while they are marginally suppressed for the same field along the a-axis. Multiple ordering in Gd based compounds is rare occurrence due to the S state nature of Gd ion and we provide a plausible scenario to explain these transitions.
Magnetism in RMn4Al8 (R = Sm, Tb, Dy and Ho) Compounds : Possible role of Mn
R Nirmalaa, V Sankaranarayanana, K Sethupathia, T Geethakumaryb, MC Valsakumarb, Y Hariharanb, AV Morozkinc
aDept. of Physics, Indian Institute of Technology,Madras -600 036, India
bMaterial Sciences Division, IGCAR, Kalpakkam, India
cDept. of Chemistry, Moscow Lomonosov State University, Moscow, Russia
The magnetic nature of ThMn12 - type, RMn4Al8 compounds is intricate and not yet completely understood. AC magnetic susceptibility studies on RMn4Al8 (R = Sm, Tb, Dy and Ho) compounds show a distinct paramagnetic to antiferromagnetic transition at temperatures less than 10 K. The shortest Mn-Mn distance being 25.8 nm, a quasi- 1-D antiferromagnetic interactions along Mn- chains of the unit cell can occur and the site occupancies of Mn atoms also might explain their magnetic behaviour.
Electronic structure and magnetism of FeGe with a B20-type structure
H. Yamadaa, K. Teraoa, H. Ohtab, E. Kulatovc
aFaculty of Science, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan
bMolecular Photoscience Research Center, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
cGeneral Physics Institute, Russian Academy of Science, Moscow, 117942, Russia
Electronic structures of FeGe with a B20-type crystal structure are calculated by a self-consistent LMTO method. A ferromagnetic state is obtained with the magnetic moment of about 1 mB per Fe at the observed lattice constant, being consistent with the observed induced moment. It is shown at smaller lattice constants that a non-magnetic semiconducting state with a very narrow band-gap becomes stable, where a magnetic field-induced metamagnetic transition takes place from a non-magnetic state (semiconductor) to a ferromagnetic one (metal), similar to that in FeSi with the same crystal structure.
Incommensurate Magnetic Structure in Copper Metaborate
G. Petrakovskiia, K. Sablinaa, M. Popova, B. Roesslib, J. Scheferb, B. Ouladdiafc, M. Boehmc
aInstitute of Physics SB RAS, 660036 Krasnoyarsk, Russia
bPaul Scherrer Institute, CH-5232, Villigen, Switzerland
cInstitut Laue-Langevin, 38042 Grenoble, Cedex 9, France
The results on the magnetic susceptibility, magnetization, specific heat, neutron scattering and mSR of the tetragonal copper metaborate single crystal are presented. The easy plane magnetic commensurate structure with the spontaneous moment was determined in the temperature range 21-10 K. The incommensurate magnetic ground state of this crystal was observed at the temperatures below 10 K until 0.15 K. It is shown the existence of a third magnetic transition below 1.8 K. The external magnetic field induces the phase transition from the incommensurate to commensurate structure. A phenomenological theory of the incommensurate magnetic structure was developed.
Effects of Structural Defects on Ferromagnetism of (La1-xCaxO)Cu1-xNixS
K. Takasea, T. Shimizua, K. Makiharaa, Y. Takahashia, Y. Takanoa, K. Sekizawaa, Y. Kuroiwab, S. Aoyagib, A. Utsumib
aCollege of Science and Technology, Nihon University, Tokyo 101-8308, Japan
bDepartment of Physics, Okayama University, Okayama 700-8530, Japan
We have studied the effect of structural defects on magnetic properties of (La1-xCaxO)Cu1-xNixS. The magnetization for stoiciometric system containing less defects decreases linearly against magnetic field with negative declination and shows diamagnetism. Any ordered phase is not observed down to 2 K. It should be noted that the ferromagnetic behavior is observed for non-stoichiometric system containing structural defects at low magnetic field. Samples belonging to the latter system exhibit a well-defined hysteresis loop at room temperature. The Curie temperature increases with x. This ferromagnetism may be attributed to carriers induced by Ni and or S deficiencies.
Magnetization and transport properties in Heusler-type Fe2TiSn compound
Miho Nakabayashia, Kazunori Fukudaa, Hiroyuki Kitagawaa, Yuh Yamadaa, Shugo Kuboa, Akiyuki Matsushitab
aDepartment of Materials Science, Shimane University, 1060 Nishikawatsu, Matsue 690-8504, Japan
bNational Research Institute for Metals, 1-2-1 Sengen, Tsukuba 305-0047, Japan
Magnetic and transport properties of Heusler-type Fe3-xTixSn (x = 0.9, 0.95, 1.0, 1.05 and 1.1) compounds have been investigated with DC magnetization, thermoelectric power and resistance measurements. The electrical resistivity of Fe3-xTixSn compounds with x = 1, 1.05 and 1.1 exhibit metallic behavior. On the other hand, Fe2.05Ti0.95Sn compound (x = 0.95) exhibits semiconductor-like behavior above the Curie temperature. These results suggest that the Fe2.05Ti0.95Sn compound should be a semimetal with a pseudgap in the density of states at the Fermi level.
Neutron scattering study in ternary intermetallic compounds Nd3Pd20Ge6 and Pr3Pd20Si6
Yoshihiro Koikea,b, Naoto Metokia, Noriaki Kimurac, Haruyoshi Aokic, Takemi Komatubarac
aAdvanced Science Research Center, JAERI, Tokai, Ibaraki 319-1195, Japan
bJapan Science and Technology Corporation, Kawaguchi, Saitama 332-0012, Japan
cCenter for Low Temperature Science, Tohoku University, Sendai 980-8577, Japan
High-field and low-temperature neutron scattering experiments have been performed in ternary intermetallic compounds Nd3Pd20Ge6 and Pr3Pd20Si6. Nd3Pd20Ge6 exhibits the antiferromagnetic ordering on 8c site with the propagation vector Q = á111ñ below TN1 = 1.8 K, while 4a site ordered antiferromagnetically with the Q = á001ñ below TN2 = 0.5 K, respectively. We present the magnetic structure and H-T phase diagram of this compound. We also report the ground state and the crystalline electric field level scheme in Pr3Pd20Si6 clarified by the neutron inelastic spectra obtained under magnetic field.
Itinerant metamagnetic properties of MnSi under high pressures
Masaki Yamadaa, Tsuneaki Gotoa, Takeshi Kanomatab
aInstitute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8581, Japan
bFaculty of Engineering, Tohoku Gakuin University, Tagajo 985-8537, Japan
Magnetization measurements of an itinerant d-electron magnet MnSi have been carried out under high pressures up to P=1.7 GPa, high magnetic fields up to B=9 T and low temperatures down to T=1.4 K. For P < 1.2 GPa, the magnetic transition is of the second-order at the transition temperature Tc. It is changed to be of the first-order for 1.2 GPa < P < 1.5 GPa. The magnetic order vanishes at the critical pressure Pc=1.54 GPa. A metamagnetic transition (MT) is observed for P ³ 1.5 GPa. It is found that the temperature T0, at which MT disappears, decreases with increasing pressure. Different types of magnetic phase diagrams of MnSi are determined in the three pressure ranges from these observed results.
Ferromagnetic Carbon with Enhanced Curie Temperature
Vladimir N. Narozhnyia,b, Karl-Hartmut Müllera, Dieter Eckerta, Angelika Teresiaka, Lothar Dunscha, Valerii A. Davydovb, Ludmila S. Kashevarovab, Alexandra V. Rakhmaninab
aInstitut für Festkörper- und Werkstofforschung Dresden e.V., 270116, D-01171 Dresden, Germany
bInstitute for HighPressure Physics, Russian Academy of Sci., Troitsk, Moscow Reg., 142190, Russia
The discovery of a ferromagnetic form of carbon [T.L. Makarova et al., Nature 413 (2001) 716] gives a new perspective in the investigation of magnetic materials. The existence of a ferromagnetic state with the very high Curie temperature TC » 500 K for a material with only s- and p-electrons as well as the nature of its underlying interaction are of great fundamental interest. Here we report on the observation of the ferromagnetically ordered state in a material obtained by high-pressure high-temperature treatment of the fullerene C60. It has a saturation magnetization more than four times larger than that reported previously. From our data we estimated the considerably higher value of TC » 820 K.
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