Resonant Two-Magnon Raman Scattering in Two-Dimensional Mott Insulators
Hiroaki Onodera, Kenji Tsutsui, Takami Tohyama, Sadamichi Maekawa
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
We investigate the resonant two-magnon Raman scattering in two-dimensional (2D) Mott insulators by using a hall-filled 2D Hubbard model. By performing numerical diagonalization calculation for a small cluster, we find that the model can reproduce the experimental features that the Raman intensity is enhanced when the incoming photon energy wi is not near the absorption edge but well above it. This is because the photoexcited states for the resonance are characterized the charge degree of freedom, while the absorption edge is by the spin degree of freedom.
Study of Phonon Anomalies in Stripe phase of High Tc Cuprates
Eiji Kaneshita, Masanori Ichioka, Kazushige Machida
Department of Physics, Okayama University, Okayama 700-8530, Japan
We theoretically investigate phonon anomalies in various high Tc cuprates in terms of stripe concept. The phonon anomalies are considered to be caused by coupling with charge translational modes of stripes. The collective stripe modes are taken into account by means of random phase approximation based on mean-field two dimensional Hubbard model, and the phonon self-energy correction was evaluated. In the result, it turns out that the coupling with stripes causes phonon dispersion gap. In this study we also investigate the oscillation modes of phonon at the gap, based on the linear response theory. The gapped branches of phonon are found to be in-phase and out-of-phase oscillations relative to the charge collective mode.
Cu-NQR study for stripe ordering in La-based cuprate
Masahiro Matsumura, Takahiro Sawa, Takayuki Tamura, Nobuyuki Yamamoto, Hideki Yamagata
Department of Material Science, Faculty of Science, Kochi University, Kochi 780-8520, Japan
Cu-NQR spectra were measured in La2-x-yMySrxCuO4, (M=Nd, Gd, Eu, Pr and Y), and La2-xBaxCuO4 with x=1/8. The low temperature tetragonal (LTT) structure is stabilized below Td2 in all the samples other than M=Pr. The usual NQR spectra observed in T > Td2 in all the samples change to abnormally broad ones after a complete wipeout of NQR signal below Td2 except for the cases of M=Nd, Gd and Pr. In the cases of M=Nd and Gd, the complete wipeout continues to 1.5 K probably due to the extrinsic nuclear relaxation path through the paramagnetic fluctuation of Nd and Gd moment. In the case of M=Pr, usual NQR spectrum continues to 1.5 K due to no structural transition to LTT phase. These results suggest a pinning in the LTT phase of stripe ordering inherently existing in the doped CuO2 plane in La-based cuprate. The common broad spectra at 1.5 K were analyzed in terms of static stripe model.
Dynamical Stripe Correlation in the d-p Model at 1/8-filling
Shigeru Koikegamia, Takashi Yanagisawab, Masaru Katoc
aJapan Society for the Promotion of Science, 6-Ichibancho, Chiyoda-ku, Tokyo 102-8471, Japan
bNanoelectronics Research Institute, AIST Tsukuba Central 2, Tsukuba 305-8568, Japan
cDepartment of Mathematical Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
We investigate the dynamical stripe correlation in the two-dimensional d-p model at 1/8-filling on the basis of the dynamical cluster approximation combined with the unrestricted fluctuation exchange approximation. We calculate the one-particle spectral function, the charge correlation function, and the spin correlation function at finite temperature. We obtain the fully self-consistent solutions near 1/8-filling. Our obtained solutions are completely metallic as far as in the one-particle picture. However, the charge and spin correlation functions reflect the existence of the quasi-one-dimensional fluctuation. This fluctuation tends to form the vertical stripe state.
Extrinsic (Bi)Polaronic Metal-Insulator Transition in Doped High-Tc Oxides
Safarali Dzhumanova, Ulugbek Kurbanova, Ryskul Yusupova, Kuanyshbek Shunkeevb
aInstitute of Nuclear Physics, 702132 Tashkent, Uzbekistan
bAktobe State University, 463000 Aktobe, Kazakhstan
Unlike the Mott and Anderson transitions the new extrinsic (bi)polaronic metal-insulator transition (MIT) in doped oxide high-Tc superconductors (HTSC) is studied within the continuum model of extrinsic carrier self-trapping and the extrinsic (bi)polaronic band model using the variational method and tight-binding approximation. The proper criterions for extrinsic Mott transition and (bi)polaronic MIT are obtained. We show that the anisotropy of the dielectric or (bi)polaronic properties of HTSC is responsible for the smooth MIT, stripe formation and suppression of high-Tc superconductivity. We explain the observed in-gap states and MIT in doped oxide HTSC in terms of the large (bi)polaron model, the extrinsic Mott transition and the extrinsic (bi)polaronic MIT and find good agreement with various experiments.
Hall coefficient anomalies in Kondo-lattice CeAl2
A.V. Bogacha, N.E. Sluchankoa, V.V. Glushkova, S.V. Demisheva, H. Ohtab, O.D. Chystyakovc
aGeneral Physics Institute of RAS, Vavilov str., 38, Moscow, 119991, Russia
bKobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
cInstitute of Metallurgy and Material Science of RAS, Leninskii Prospect, 49, Moscow, 117334, Russia
Anomalous Hall effect in paramagnetic and modulated antiferromagnetic (AFM) phases of a Kondo-lattice CeAl2 has been studied in a wide range of temperatures (1.8-300K) and magnetic fields (up to 80 kOe). It is shown that the large anomalous skew scattering component RHa has a broad maximum around T » 4K depressing by a factor of 3 in H » 80 kOe. The non-monotonous behavior of magnetic components RHam in magnetic field below 40 kOe and a narrow maximum of RHam(T) at T=TN » 3.85K are likely to be attributed to the AFM-domains reorientation process at liquid helium temperatures. The problem of two magnetic phase transitions in CeAl2 is discussed from the point of view of the data obtained.
Low-frequency noise in intermediate valent compound SmB6
V. Glushkova, N. Sluchankoa, S. Demisheva, S. Safonovb, A. Savchenkob, H. Ohtac, S. Kuniid
aGeneral Physics Institute of RAS, Vavilov str., 38, Moscow, 119991, Russia
bPhysics Department, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
cKobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
dDepartment of Physics, Tohoku University, Sendai, Japan
The study of the noise characteristics along different crystallographic directions in the intermediate valence compound SmB6 revealed the strong anisotropic enhancement of the low-frequency resistance noise at T < 15K. The noise voltage temperature dependencies in SmB6 demonstrate a broad maximum at T » 11K which is very similar to the anomaly in the Hall mobility1. The anomalies observed are discussed in terms of a many-body states formation resulting from fast valence fluctuations on Sm-sites.
Magnetotransport in (Y1-xGdx)Co2 alloys near to magnetic phase boundary
Alexander Burkova, Alexander Zyuzinb, Joachim Schumanna, Hartmut Vinzelberga, Takao Nakamac, Masato Hedoc, Katsuma Yagasakic
aInstitute of Solid State and Materials Research Dresden P.O.Box 270016, D-01701, Dresden, Germany.
bA. F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, Sankt-Petersburg 194021, Russia.
cPhysics Department, University of the Ryukyus, Okinawa 903-0213, Japan.
We present experimental results on magnetotransport in (Y1-xGdx)Co2 alloys, where the localized Gd-moments are coupled antiferromagnetically to the itinerant Co 3d electrons. The alloys are paramagnetic for x < 0.15. The transport properties of the paramagnetic alloys show Kondo like anomalies. On approaching to the magnetic phase boundary the resistivity reveals non-Fermi liquid behaviour, indicating a presence of apparently gap-less magnetic excitations. Large positive magnetoresistivity is observed in in the alloys with magnetic ground state at temperatures T < Tc.
Gap formation in the semimetal U2Ru2Sn: 119 Sn NMR investigations
M. Baenitza, A. Rabisa, S. Paschena, V.H. Trana, F. Steglicha, P. de V. duPlessisb, A.M. Strydomc
aMPI für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, D - 01187 Dresden
bDepartment of Physics, University of the Witwatersrand PO Wits 250, Johannesburg, South Africa
cDepartment of Physics, Rand Afrikaans University, PO 524, Johannesburg, South Africa
We report measurements of the 119Sn spin - lattice relaxation rate 1/T1 and the Knight shift K for U2Ru2Sn. The T dependence of 1/T1 is very similar to that of CeNiSn with the only difference that the T scale is increased roughly by a factor of 10. Therefore a first estimate gives a gap value of D/ kB » 140 K ( » 14 K for CeNiSn). At low temperatures a T1T=constant behaviour is observed similar to CeNiSn. Furthermore, measurements on the 119Sn Knight shift, the susceptibility, the specific heat, the electrical resistivity and the Hall coefficient are discussed in the context of a gap formation due to correlations in this semimetal. Investigations on the non-magnetic reference compound Th2Ru2Sn are also presented.
Photoemission study of CeTIn5 (T=Rh, Ir)
S.-i. Fujimoria, J. Okamotoa, K. Mamiyaa, T. Okanea, A. Fujimoria,b, T. Narimurac, K. Kobayashic, K. Shimadac, H. Namatamec, M. Taniguchic, H. Harimad, D. Aokie, S. Ikedaf, H. Shishidof, Y. Tokiwag, Y. Hagag, Y. ¯Onukif,g
aJapan Atomic Energy Research Institute, SPring-8, Hyogo 679-5148, Japan
bGraduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
cHiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
dInstitute of Scientific and Industrial Research, Osaka University, Osaka 567-0043, Japan
eDRFMC-SPSMS, CEA, 38054 Grenoble Cedex 9, France
fGraduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
gAdvanced Science Research Center, Japan Atomic Energy Research Institue, Ibaraki 319-1195, Japan
The electronic structures of CeTIn5 (T=Rh, Ir) have been investigated by photoelectron spectroscopy.
Thermal, magnetic, and transport properties of U2Ru2Sn
S. Paschena, V. H. Trana, N. Senthilkumarana, M. Baenitza, F. Steglicha, A. M. Strydomb, P. de V. du Plessisc, G. Motoyamad, N. K. Satod
aMax Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
bPhysics Department, Rand Afrikaans University, PO Box 524, Johannesburg, South Africa
cPhysics Department, University of the Witwatersrand, PO Wits 2050, Johannesburg, South Africa
dDepartment of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
U2Ru2Sn shares several properties with the strongly correlated semimetal CeNiSn. Here, we present measurements of thermal, magnetic, and transport properties of both poly- and single-crystalline samples. The specific heat provides evidence for the opening of an energy gap of approximately 160 K. Both the magnetic susceptibility and the electrical resistivity are anisotropic, suggesting that the energy gap opens primarily in the basal plane of the tetragonal compound U2Ru2Sn.
High Field Magnetoresistance in Heavy Fermion Superconductor PrOs4Sb12
Hitoshi Sugawara, Shuji Osaki, Eiich Kuramochi, Miki Kobayashi, Shanta R. Saha, Takahiro Namiki, Yuji Aoki, Hideyuki Sato
Graduate School of Science, Tokyo Metropolitan University, Minami-Ohsawa, Hachioji, Tokyo 192-0397, Japan
PrOs4Sb12 is recently found to show superconductivity below TC=1.85 K, in which the large specific heat jump at TC (DC/TC ~ 500 mJ/K2· mol) suggests the strong electronic correlation. We have succeeded in growing high quality single crystals of PrOs4Sb12 and measured the magnetoresistance (MR) upto 14 T. The field dependences of transverse MR are found to saturate for the whole field angular directions indicating that this compound is uncompensated metal with the closed Fermi surface. We have found the anomalous high field phase at 4 ~ 12 T below 1.25 K which is also found in the specific heat measurements under the magnetic fields.
Thermal Expansion of UCu2Sn in the Basal Plane
Isao Ishii, Takashi Suzuki, Haruhiro Higaki, Kenichi Katoh, Toshiro Takabatake, Toshizo Fujita
Department of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
We reported from the elastic moduli experiments that the hexagonal uranium compound UCu2Sn undergoes a forroquadrupolar ordering of non-Kramers doublet G5 at TQ=16 K. However, a macroscopic strain has not been measured by a X-ray diffraction experiment because the strain is expected to be smaller than the experimental resolution due to the weak coupling between the strain and order parameters 2. To detect the spontaneous strain, we carried out a thermal expansion measurement by a capacitance method with higher resolution from 4.2 to 40 K. The thermal expansion in the basal plane shows a remarkable change below TQ, suggesting the emergence of the eG5 strain which couples to G5.
Spin fluctuations in heavy-Fermion compounds YbZnCu4 and YbAuCu4, investigated by 63Cu NMR/NQR
Takehide Koyamaa, Takeshi Mitoa, Shinji Wadaa, John L. Sarraob
aGraduate School of Science and Technology, Kobe University, Nada, Kobe 657-8501, Japan
bLos Alamos National Laboratory, Mail stop K 764, Los Alamos, NM 87545, USA
We have investigated spin fluctuations of the Yb 4f hole in heavy Fermion compounds close to localized spin regime: YbZnCu4 (TK @ 30 K) and YbAuCu4 (TK @ 1.6 K). The Curie-Weiss-type behavior of both isotropic and anisotropic Knight shifts for each of the compounds is indicative of Yb3+ ionic state. Correlation time tf of Yb spin fluctuations in YbZnCu4 is found to be ~ 10-13 sec and independent of the temperature for 1.4-100 K, due to an extremely small mixing between f electrons and conduction electron density. While in YbAuCu4, the temperature-independent tf ~ 10-12 sec at high temperatures begins to decrease around ~ 40 K, and approaches ~ 10-11 sec which corresponds to kBTK in energy.
Observation of cyclotron resonance in CeSb
Mitsuhiro Motokawaa, Makoto Yoshidaa, Keiich Koyamaa, Takahiro Tomimatsua, Makoto Shirakawab, Akira Ochiaib
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 CeSb have been performed in the temperature range from 1.6 to 20 K in the frequency range from 50 to 110 GHz. We have successfully observed several absorption lines of cyclotron resonance. The estimated effective masses are in the range of 0.28-1.5m0, and they are compared with the masses estimated from dHvA effect measurements. It is the first observation of cyclotron resonance on strongly correlated f-electron systems.
Spin-glass Behavior in Ternary Uranium Compound U2AuGa3
T. Yamamura, D. X. Li, Y. Shiokawa
Institute of Materials Research, Tohoku University, Sendai, Miyagi 980-8577, Japan
The magnetic properties of the intermetallic compound U2AuGa3 were investigated on well-annealed polycrystalline samples by DC magnetization, specific heat and magnetic relaxation measurements. The temperature dependence of magnetization shows irreversibility and the frozen-in magnetic moment was observed below a characteristic temperature Tf=23 K. The temperature dependence of specific heat does not show visible singularity indicating the absence of long-range magnetic order around Tf. Furthermore, more than 50% of the remnant magnetization is observed even after 3 hours due to long-time magnetic relaxation effect. These results clearly indicate that U2AuGa3 undergoes spin-glass transition at Tf.
Non-Fermi-Liquid Behavior in Amorphous UPd2Al3
Takashi Ohnoa, Yutaka Kishimotoa, Yasuhisa Ushidab, Yoshiya Hommac, Yoshinobu Shiokawac, Takashi Nishiokac, Masaaki Kontanib
aFaculty of Engineering, Tokushima University, Tokushima 770-8506, Japan
bGraduate School of Science, Nagoya University, Nagoya 454-8602, Japan
cInstitute for Material Research, Tohoku University, Sendai 980-8577, Japan
These ten years, unusual behaviors in physical quantities different from Fermi liquid state have been reported in many heavy Fermion materials. Some experimental results have been explained from the disorder-induced non-Fermi-liquid theories. To investigate non-Fermi-liquid state further, a crystallographycally disordered amorphous UPd2Al3 has been prepared. Electrical resistivity and specific heat observed in an amorphous UPd2Al3 show anomalous behaviors at low temperatures, which are discussed by connecting with non-Fermi-liquid state and comparing with those observed in a crystalline UPd2Al3.
Transport properties of the dense Kondo system Ce0.5La0.5B6
Shintaro Nakamuraa, Ryo Satoa, Tsutomu Nojimaa, Haruyoshi Aokia, Satoru Kuniib
aCenter for Low Temperature Science, Tohoku University, Sendai 980, Japan
bDepartment of Physics, Tohoku University, Aramaki Sendai 980-8578, Japan
CexLa1-xB6 is well known as a cubic dense Kondo system. The ground crystal electric field state is a G8 which carries both magnetic dipolar and electric quadrupolar moments. No long range ordering have been found in Ce0.5La0.5B6 down to ~ 20 mK under low fields, and an antiferromagnetic or an antiferroquadrupole ordering is induced by applied magnetic fields. We present the transport properties of Ce0.5La0.5B6 at low temperatures. The resistivity of Ce0.5La0.5B6 follows the formula AT2+const. in the low temperature region. This suggests the formation of a strongly correlated Fermi liquid.
Kondo Effect in Two-Dimensional Disordered Systems
Sei-ichiro Suga, Takuma Ohashi
Department of Applied Physics, Osaka University, Suita, Osaka 565-0871, Japan
We investigate the Kondo effect in two-dimensional disordered electron systems on the basis of the single-impurity Anderson model with on-site random potentials. Using a finite-temperature quantum Monte Carlo method, we calculate the susceptibility of a magnetic impurity. Depending on the position of a magnetic impurity, its local moment can be screened or unscreened by the spin of the conduction electron. In the former case, the susceptibility shows a local Fermi-liquid behavior, while in the latter case, the susceptibility shows a power-law or a logarithmic divergence. From the results, we show that the Kondo temperaturet TK is distributed more widely and the weight at TK=0 becomes larger as randomness increases. The average susceptibility shows a weak power-law divergence at low temperature in strongly disordered systems, indicating a non-Fermi liquid behavior.
De Haas - van Alphen effect under pressure in URu2Si2
Miho Nakashimaa, Shugo Ikedaa, Tomoyuki Okuboa, Yoshihiko Inadaa, Rikio Settaia, Hitoshi Ohkunia, Etsuji Yamamotob, Yoshinori Hagab, Yoshichika ¯Onukia
aGraduate School of Science, Osaka University, Osaka 560-0043, Japan
bAdvanced Science Research Center, Japan Atomic Energy Research Institute,Ibaraki 319-1195, Japan
A tiny moment of 0.03 mB/U in URu2Si2 is found to increase as a function of pressure and to have a small jump at 1.5 GPa, reaching 0.4mB/U. The recent NMR experiment claimed that this corresponds to an increase of the antiferromagnetic region with the moment of 0.4mB/U. We have done the de Haas-van Alphen (dHvA) effect under pressure up to 1.8 GPa. The present dHvA result is inconsistent with the NMR experiment because a new Fermi surface does not appear under the corresponding pressure, indicating a slight increase of the volume of the Fermi surface and a decrease of the cyclotron mass with increasing the pressure.
Magnetic-Field Effects on the Pseudogap in CeRhAs
Shunsuke Yoshiia, Koichi Kindoa, Tetsuya Sasakawab, Toshiaki Suemitsub, Toshiro Takabatakeb
aKYOKUGEN,Osaka University,Toyonaka,Osaka 560-8531,Japan
bDepartment of Quantum Matter,ADSM,Hiroshima University,Higashi-Hiroshima 739-8530,Japan
The electrical resistivity and magnetization of single crystal CeRhAs, which is the so-called Kondo insulator, have been investigated in magnetic fields up to 55T. In the field region below 20T, anisotropic behaviors are observed in both transport and magnetic properties. Especially, the longitudinal magnetoresistance along the b and c axes show anomalous drops following with minima, while it decreases monotonically after a broad maximum in the a direction.These behaviors may be attributed to the existence of a narrow structure with an anisotropic nature inside the wide pseudogap.
NMR Studies of YbB6
J. L. Gavilanoa, Sh. Mushkolaja, D. Raua, H. R. Otta, A. Bianchib, Z. Fiskb
aLaboratorium für Festkörperphysik, ETH-Hönggerberg, CH-8093 Zürich, Switzerland
bNational Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306
We have performed dc-magnetisation and 11B-NMR measurements on single crystalline YbB6. The magnetisation data at temperatures between 4 and 300 K reveal the presence of ferromagnetic order with a TC > 300 K and involving very small ordered moments, i.e., 0.002mB/f.u. This value represents only a small fraction of the effective paramagnetic moment, per formula unit, that is evidenced in the results for the magnetic susceptiblity. The latter can be accounted for by assuming that only 2% of all the Yb atoms adopt the Yb+3 configuration. The 11B spin-lattice relaxation rate has a substantial contribution of the form T1-1(T) µ T indicating that YbB6 has a distinct metallic character, somewhat unexpected if it is considered that almost all the Yb ions adopt the divalent configuration.
Kondo lattice behaviour of CeNi9Si4
Gerfried Hilschera, Herwig Michora, Ernst Bauera, Peter Roglb
aInstitut für Festkörperphysik, Technische Universität Wien, A-1040 Wien, Austria
bInstitut für Physikalische Chemie, Universität Wien, A-1090 Wien, Austria
We have studied the phase formation, thermodynamic and transport properties of ternary compounds RNi9Si4 (R = La and Ce) with tetragonal crystal structure (space group I4/mcm). For CeNi9Si4 resistivity, magnetic susceptibility and specific heat measurements reveal Kondo-lattice properties with a T2 temperature dependence of the electrical resistivity, A ~ 0.01mWcm/K2, an enhanced Sommerfeld value g = 160 mJ/molK2. The Kadowaki-Woods ratio A/g2 ~ 0.4×10-6mWcm(molK/mJ)2 indicates weak RKKY coupling of the Ce-moments. The magnetic contribution to the specific heat and the magnetic susceptibility is analysed in terms of the Coqblin-Schrieffer model with a fully degenerate J = 5/2 ground state and a characteristic temperature T0 @ 180 K.
Electronic structure and the Fermi surface of UTGa5 (T=Fe, Co, Rh)
Takahiro Maehiraa, Masahiko Higuchib, Akira Hasegawac
aAdvanced Science Research Center, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki 319-1195, Japan
bDepartment of Physics, Tohoku University, Sendai, Miyagi 980-8576, Japan
cFaculty of Science, Niigata University, Niigata, Niigata 950-2181, Japan
The relativistic augmented plane wave band calculations have been carried out for UFeGa5, UCoGa5 and URhGa5 under the assumption that 5f-electrons are itinerant. The hole sheets of the Fermi surface in the 14th band are all small in size and closed in topology. The electron sheets of the Fermi surface in the 15th band are cylindrical and looks like a lattice-structure surface. The origins of the de Haas-van Alphen frequency branches in UFeGa5 have been clarified satisfactorily well.
The result for band calculations and the Fermi surface for UCoGa5 and URhGa5 is also presented.
High-resolution, low-temperature photoemission spectroscopy of Kondo semiconductor CeRhAs and related compounds
Kenya Shimadaa, Kenichi Kobayashib, Takamasa Narimurab, Peter Baltzera, Hirofumi Namatamea, Masaki Taniguchia, Toshiaki Suemitsuc, Tetsuya Sasakawac, Toshiro Takabatakec
aHiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-8526, JAPAN
bGraduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, JAPAN
cDepartment of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima 739-8526, JAPAN
We present and discuss the Ce 4f derived electronic states near the Fermi level of the Kondo semiconductor CeRhAs, the Kondo semimetal CeRhSb, and the Kondo metal CePtSn obtained by high-resolution (DE = 16-20 meV), low-temperature (10-12 K) resonant photoemission spectroscopy with a photon energy of hn = 122-126 eV.
Temperature Dependent Hyperfine Interactions in CePdAl
Akira Oyamadaa, Masahide Nishiyamaa, Kazuo Kamiokaa, Satoru Maegawaa, Takao Gotoa, Hideaki Kitazawab
aGraduate School of Human and Environmental Studies, Kyoto University, Kyoto, 606-8501 Japan
bNational Institute for Materials Science, Tsukuba, 305-0047 Japan
Nuclear Magnetic Resonance have been performed to study hyperfine interactions in CePdAl. The temperature dependence of Knight shift(K) and susceptibility(c) is highly anisotropic as expected from its crystal structure. Non-linearity of K - c plot was observed only when the magnetic field was perpendicular to c-axis. Two dimensional short range correlations are discussed.
Fermi surface of the periodic Anderson model by momentum-resolved charge compressibility
Y. Otsukaa, Y. Hatsugaib
a Department of Applied Physics, University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-8656, Japan
b Dept. of Applied Physics Univ. of Tokyo and PRESTO, JST, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan
We investigate a Fermi surface of the periodic Anderson model by the finite temperature quantum Monte calro method. Although the Luttinger sum rule predicts the system has a large Fermi surface (at T=0 ) which contains both conduction and f electrons, the momentum distribution function n(k) at a finite temperature shows large change at a small Fermi surface which contains only the conduction electrons without the f electrons and a clear signature of the large Fermi surface is not easily observed. On the other hand, the momentum-resolved compressibility [ d n(k)/(d m)] which reflects effects of an infinitesimal doping shows a peak structure at the large Fermi surface even at an easily accessible temperature.
Neutron-Diffraction Study of the Unusual Ordered Phases of Ce0.75La0.25B6
Kazuaki Iwasaa, Keitaro Kuwaharaa, Masahumi Kohgia, Peter Fischerb, Andreas Dönnib, Thomas C. Hansenc, Satoru Kuniid
aDepartment of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan
bETH Zurich & Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
cInstitut Laue-Langevin, 38042 Grenoble Cedex 9, France
dDepartment of Physics, Tohoku University, Sendai 980-8578, Japan
Ce0.75La0.25B6 shows paramagnetic phase (phase I), 4f-electron quadrupolar ordered phase (II), magnetically ordered phase (III), and unknown phase IV. In order to investigate order parameters in these phases, neutron diffraction experiments have been performed down to 74 mK. The order parameter in phase IV is not a magnetic dipole, and magnetic structure in phase III is different from that previously suggested for CeB6 (Effantin et al.). These facts indicate an importance of 4f-electron multipole effect.
The Coexistence of Magnetism and Superconductivity in CeRhIn5
Donavan Halla, S. W. Tozera, E. C. Palma, T. P. Murphya, R. G. Goodrichb, J. L. Sarraoc
aNational High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
bLouisiana State University, Baton Rouge, LA, USA
cLos Alamos National Laboratory, Los Alamos, NM, USA
The heavy fermion system CeMIn5, where M is either Rh, Ir, or Co exhibits the coexistence of magnetism and superconductivity. CeRhIn5 has an antiferromagnetic ground state giving way through a first order phase transition to a superconducting state with a critical temperature of 2.2 K under the application of 16 kbar of pressure. We have measured the evolution of the Fermi surface of CeRhIn5 as a function of pressure. Experimental methods and results will be presented.
Metamagnetic transistions in the Heavy Fermion Superconductors CeIrIn5 and CeCoIn5
E. C. Palma, T. P. Murphya, Donavan Halla, S. W. Tozera, R. G. Goodrichb, J. L. Sarraoc
aNational High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
bLouisiana State University, Baton Rouge, LA, USA
cLos Alamos National Laboratory, Los Alamos, NM, USA
The recently discovered heavy fermion materials CeMIn5, where M is either Rh, Ir, or Co have proven to be an interesting class of materials with a rich phase diagram involving magnetism and superconductivity. In particular the superconductivity in CeIrIn5 and CeCoIn5 occurs at ambient pressure with transition temperatures of 0.4 K and 2.3 K respectively. We will present data taken at temperatures from 20 mK and DC magnetic fields up to 45 T on the metamagnetic transitions in these materials and the effects on the fermi surface determined by dHvA measurements both below and above the metamagnetic transitions.
Spin Fluctuations on YbRh2Si2 in the Vicinity of a Quantum-Critical Point Revealed by 29Si NMR
K Ishida*a, K Okamotoa, Y Kawasakia, Y Kitaokaa, O Trovarellib, C Geibelb, F Steglichb
aDepartment of Physical Science, Osaka Univ., Toyonaka, Osaka 560-8531, Japan
bMPI for Chemical Physics of Solids, D-01187 Dresden, Germany
We report a 29Si NMR study on aligned single crystals of YbRh2Si2 shows behavior characteristic of the system of the vicinity of a quantum critical point (QCP: TN ® 0). K and 1/T1T of Si show a strong dependence on the external field H, especially below 5 kOe. At the lowest field used in this measurement (H ~ 1.5 kOe), it was found that 1/T1T continues to increase down to 50 mK, whereas K stays constant with a large magnitude below 200 mK. This result strongly suggests the development of antiferromagnetic fluctuations with finite q vectors that compete with q = 0 spin fluctuations in the vicinity of the QCP near H = 0.5 kOe. *Present address: Dept. of Phys. Kyoto Univ. Kyoto 606-8502, Japan.
Instability of RKKY-type long-range order in Kondo-lattice compound
Ce(Ru0.9Rh0.1)2(Si1-yGey)2 as studied by neutron diffraction
Shuzo Kawarazakia, Kenji Watanabea, Yoshiya Uwatokob, Hiroaki Kadowakic, Yoshikazu Tabataa, Toshifumi Taniguchia, Chikahide Kanadania
aGraduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
bInstitute for Solid State Physics, The University of Tokyo, Kahiwa-shi, Chiba 277-8581, Japan
cDepartment of Physics, Tokyo Metroporitan University, Hachioji, Tokyo 192-0397, Japan
Neutron diffraction measurements have been made to study the response of the magnetic order of the heavy-fermion compound Ce(Ru0.9Rh0.1)2(Si1-yGey)2 to hydrostatic pressure and to the chemical-pressure. With changing the Ge concentration, both of the magnitude of the magnetic moment and the value of the wave number show rapid change at around y=0.08. The 3rd harmonic component of the modulation of the y=0.2 compound clealy exhibits localized-electron nature at low temperature.
Specific heat study of non-Fermi liquid behavior in CexLa1-xPd2Al3
Shijo Nishigoria, Masaru Katsubeb, Takashi Itob, Akiyuki Matsushitac
aInstrumental Analysis Center, Shimane University, Matsue 690-8504, Japan
bDepartment of Material Science, Shimane University, Matsue 690-8504, Japan
cNational Institute for Materials Science (NIMS), Tsukuba, 305-0047, Japan
We have measured specific heat of CexLa1-xPd2Al3 (0 £ x £ 1.0) from 0.4 to 100 K. The magnetic specific heat normalized to a mole of Ce divided by temperature, Cm/T, for x= 1.0 shows a peak at 3.0 K which is attributed to the antiferromagnetic (AF) transition. With decreasing x, the peak shifts to lower temperatures. For x= 0.7, a logarithmic diverdence in Cm/T is observed below 7 K simultaneously with the disappearance of AF transition. This suggests that the non-Fermi liquid behavior appears due to the magnetic instability. With further decreasing x, Cm/T shows the same temperature dependence as that for x= 0.7 in the wide Ce concentration range down to x= 0.3.
Magnetic Excitations in uranium based 5f systems
Naoto Metokia,b, Yoshihiro Koikea,c
aAdvanced Science Research Center, JAERI, Tokai, Ibaraki 319-1195, Japan
bGraduate School of Science, Tohoku University, Sendai 980-8577, Japan
cJapan Science and Technology Corporation, Kawaguchi, Saitama 332-0012, Japan
We will review the results of our recent inelastic neutron scattering studies on uranium based intermetallic compounds. The high energy response is strongly dependent on the nature of 5f electrons. We observed clear cross over from localized to itinerant regime, namely distinct spin wave, crystalline electric field, and J-multiplet were observed in a localized system, while broad magnetic continuum with opening gap below TN would be a signiture for the itinerant 5f character. The existence of a quasi-elastic response would be the evidence for the quasi-particles even in a localized system.
de Haas-van Alphen Effect on CeRh3B2
Yoshihiko Inada, Almgham Thamizhavel, Shingo Kirita, Tomoyuki Ohkubo, Mineko Yamada, Yoshichika ¯Onuki
Graduate School of Science, Osaka University, Toyonaka, 560-0043 Japan
CeRh3B2 has the highest Curie temperature of 115 K in all the cerium compounds, although a saturation moment is only about 0.4mB/Ce being much smaller than the moment based on the crystalline electric field. It is important to reveal whether the 4f electron has the itinerant charactor or not and the role of Rh d band in this compound.
We succeeded in growing high-quality single crystals of CeRh3B2, and in observing the de Haas-van Alphen (dHvA) effect. The dHvA frequencies are in the range from 400 ~ 2000 T and some branches indicate the existence of closed Fermi surfaces.
11B NMR Study in the Antiferromagnetic Phase III of Ce0.75La0.25B6
Kiyoshi Mizunoa, Ko-ichi Magishia, Masayuki Kawakamib, Takahito Saitoa, Kuniyuki Koyamaa, Satoru Kuniic
aFaculty of Integrated Arts and Sciences, The University of Tokushima, Tokushima 770-8502, Japan
bDepartment of Physics, Kagoshima University, Kagoshima 890-0065, Japan
cDepartment of Physics, Tohoku University, Sendai 980-8578, Japan
We have carried out the 11B NMR experiments on a single crystalline sample of Ce0.75La0.25B6 in order to elucidate the magnetic structure of the antiferromagnetic phase III and compare with the result of CeB6. It is very important to investigate the magnetic property in phase III neighboring the unknown phase IV. In phase III, the spectrum is well reproduced by Sakai model, which reproduces the spectrum in phase III of CeB6. It suggests that phase III of Ce0.75La0.25B6 is similar to that of CeB6. The more detailed experiments and analyses are now in progress. We will report those results at the presentation.
One-Loop Corrections to the Susceptibility and the Specific Heat in the Periodic Coqblin-Schrieffer Model
Keiichi Oharaa, Katsurou Hanzawab
aKurashiki City College, Kurashiki 711-0911, Japan
bTokyo University of Science, Noda 278-8510, Japan
The periodic Coqblin-Schrieffer model with isotropic hybridization is investigated in the one-loop approximation for the half-filled case in terms of the functional integral formalism. We determine the order parameter corresponding to heavy fermion state and calculate the thermodynamic quantities such as susceptibility and specific heat. We discuss the fluctuation effects to the thermodynamic quantities comparing with the results obtained in the mean-field approximation.
mSR Study of Magnetism of CeRh2Si2 under High Pressure
Wataru Higemotoa, Kazuhiko Satohb, Atsushi Hanaokab, Akihiro Kodaa, Kusuo Nishiyamaa, Koichiro Shimomuraa, Ryosuke Kadonoa, Sadayoshi Koiwaib, Yoshiya Uwatokoc, Nobuo Morib
aInstitute of Materials Structure Science, KEK, Ibaraki 305-0801, Japan
bDepartment of Physics, Saitama University, Saitama 338-8570, Japan
cInstitute of Solid State Physics, University of Tokyo, Chiba 277-8581, Japan
CeRh2Si2 shows two antiferromagnetic transitions at ambient pressure (TN1=36K and TN2=27K). Application of pressure suppresses TN to 0K at Pc ~ 1GPa. We study the magnetism of the single crystalline sample of CeRh2Si2 by mSR method up to 0.4GPa. At T < TN2, we observed both the spontaneous muon spin precession and the fast muon spin relaxation under a zero magnetic field. Although the transition temperature decreases with increasing the pressure, the precession frequency, which is proportional to the saturated sublattice magnetic moment, is nearly independent on the pressure.
Effect of Pressure on Yb1-xYxInCu4 with First-order Valence Transition
Wei Zhanga, Kazuyoshi Yoshimuraa, Akihiro Mitsudab, Nikolay V. Mushnikovb, Tsuneaki Gotob
aDepartment of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
bInstitute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
At transition temperature (Tv » 42 K) YbInCu4 exhibts a first-order isostructural valence transition from Yb3+ free ion state at high temperature (HT) with Kondo temperture TKH= 25 K to intermediate valence state (Yb2.9+) at low temperature (LT) with Kondo temperature TKL= 400 K. In LT phase this transition also can be induced by high magnetic field with transition magnetic field (Hv) » 33 T or by pressure with transition pressure (Pv » 20 kbar). Although the Yb1-xYxInCu4 system make the lattice parameter of YbInCu4 increase with the Y substitution, it shows a steep decrease of Tv and Hv, resulting in suppression of the valence transition around x=0.3. The effect of pressure on Yb1-xYxInCu4 will be reported.
Pressure effect on transport properties in heavy Fermion semimetal CeRu4Sb12
Miki Kobayashi, Shanta R. Saha, Hitoshi Sugawara, Takahiro Namiki, Yuji Aoki, Hideyuki Sato
Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan
CeRu4Sb12 has been reported to exhibit Non-Fermi-liquid (NFL) behavior at low temperatures [1]. The origin has not yet been clarified. Based on the transport and Shubnikov-de Haas (SdH) experiments, Fermi surface (FS) is large at high temperatures similar to LaRu4Sb12 [2], while at low temperatures it becomes a small semi-metallic one with highly enhanced effective mass. In order to understand such exotic behaviors, we have investigated the effect of pressure on the transport properties including the direct observation of FS using SdH effect. NFL behavior is easily destroyed both by magnetic field and pressure, though the pressure effect is minor at high temperatures. The SdH experiment under uniaxial pressure revealed that the nearly spherical FS is elongated along the pressure direction. [1] N. Takeda and M. Ishikawa: J. Phys. Soc. Japan 69 (2000) 868. [2] K. Abe et al.: to be published in Physica B.
Anomalous Hall Effect in Heavy Fermion Compounds Ce2TIn8 (T = Rh or Ir)
Isao Sakamoto, Yoshinobu Shomi, Shigeo Ohara
Department of Electrical and Computer Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
Ce2RhIn8 and Ce2IrIn8 are newly-found heavy fermion compounds. These materials are crystallized in the tetragonal Ho2CoGa8-type structure where the 2-layers of CeIn3 and a layer of RhIn2 or IrIn2 are piled up alternately along the c-axis. We have grown a series of compounds R2TIn8 in single crystal form, where R = La, Ce or Pr, and T = Rh or Ir. The measurements of the magnetic susceptibility, the electrical resistivity and the Hall effect were performed in the temperature range between 2-300 K. In this contribution, we report the anomalous Hall effect in Ce2TIn8, compared with the data for the isostructural non-magnetic La2TIn8 and paramagnetic Pr2TIn8 which posses a singlet ground state.
Magnetic and Fermi Surface Properties of UTGa5 (T : Fe , Co and Pt)
Shugo Ikedaa, Yoshihumi Tokiwaa, Tomoyuki [`(O)]kuboa, Mineko Yamadaa, Tatuma D. Matudab, Yoshihiko Inadaa, Rikio Settaia, Etuji Yamamotob, Yoshinori Hagab, Yoshichika [`(O)]nukia
aGraduate School of Science, Osaka University, Toyonaka, Osaka 560-00 43, Japan
bAdvanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan
We succeeded in growing a high-quality single crystal of the UTGa5 (T : Fe, Co and Pt) by the self-flux method, and measured the de Haas-van Alphen (dHvA) effect, together with the electrical resistivity, magnetoresistance, magnetic susceptibility and specific heat. Reflecting the unique tetragonal crystal structure, the Fermi surface in a paramagnet UFeGa5 and an antiferromagnet UPtGa5 consist of cylindrical Fermi surfaces and a lattice like Fermi surface. On the other hand, UCoGa5 is the semimetal where Fermi surface consists of small closed Fermi surfaces.
Effect of Pressure on the Electrical Resistivity of Heavy Fermion Antiferromagnet Ce2RhIn8
Shigeo Ohara, Yoshinobu Shomi, Isao Sakamoto
Department of Electrical and Computer Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
The heavy fermion family CenRhIn3n+2 have attracted much attention since the CeIn3 (n=¥) and CeRhIn5 (n=1) become superconductors under high pressure. Ce2RhIn8, which is the n=2 member of this family, is a heavy fermion antiferromagnet, TN=2.8 K. We have grown a single crystal of Ce2RhIn8 and measured the electrical resistivity under high pressures up to 16 kbar in temperature range 1.5-300 K. At ambient pressure, the resistivity of Ce2RhIn8 increases logarithmically with decreasing temperature until it reaches a maximum at 5 K and show a shoulder at TN. It is found that the resistive signature for TN decreases with pressure. At 16 kbar, magnetic order is not observed down to 1.5 K.
Scanning SQUID microcopy of superconducting La2-xSrxCuO4 single crystals
Kazuyuki Isawaa, Mitsugu Naganoa, Kazuhiko Ikeuchib, Kazuyoshi Yamadab
aResearch and Development Center, Tohoku Electric power Co., Inc., 2-1 Nakayama 7-chome, Aoba-ku, sendai, 981-0952, Japan
bInstitute of Chemical Research, Kyoto University, Gokasho, Uji 611-0011, Japan
The recent report on the existence of diamagnetic domains in La2-xSrxCuO4 (LSCO) thin films above Tc was stimulating, though the phenomena was not observed in successive measurements on bulky specimens. To clinch the controversy, we have measured local magnetic images of LSCO single crystals utilizing scanning SQUID microscope. For the LSCO single crystals with x=0.14-0.16, the vortex patterns were clearly observed at 3K. These patterns persisted up close to Tc, though they totally diminished at temperatures above 40K. Measurements on the underdoped and highly overdoped samples are in progress.
Effect of orbital degeneracy on magnetic phases of electron-doped manganites
Sergey M. Dunaevsky, Vladimir V. Deriglazov
Petersburg Nuclear Physics Institute, Gatchina 188300, Russia
The total energies for various magnetic structures of electron doped manganites are evaluated using energy bands E(k) accounting for the orbital degeneracy of eg-band of manganese for the main A-, C- and G-types of antiferromagnetic ordering. To determine the magnetic configuration, minimization of the ground state energy with respect to the canting angle between the spins of Mn4+-ions of the two magnetic sublattices has been performed. It appeared that in the case of complete degeneracy of eg-orbital the calculated magnetic phase diagrams fail to explain the experimentally observed arrangement of magnetic phases. The account of rather small splitting of eg-level drastically changes the phase diagrams retrieving their compatibility with experimental observations in the realistic region of parameters even in the collinear approximation.
Scanning SQUID Microscopy on composition-spread NdSrMnO films under irradiation
Hidetaka Sugayaa, Tae-Youb Kimb, Jun Nishimuraa, Tomoteru Fukumurac, Masashi Kawasakic, Hideomi Koinumaa, Yoshinori Tokurad, Tetsuya Hasegawaa
aTokyo Institute of Technology, Midori-ku, Yokohama 226-8503, Japan
bCOMET, Advanced Materials Lab., National Institute for Materials Science, Tsukuba 305-0044, Japan
cInstitute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan
dDepartment of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
Local magnetic properties of composition-spread Nd1-xSrxMnO3 (NSMO; x=0.4-0.6) films were surveyed by a scanning SQUID microscope under irradiation. We have found that the spontaneous magnetization of the FM phase is drastically enhanced by the laser irradiation (l=532nm), while that of the CO region is rather unchanged.
Magnetic inhomogeneity effects in DC transport properties and microwave absorption of La0.5Sr0.5CoO3-d film
Boris I. Belevtseva, Nickolay T. Cherpakb, Irina N. Chukanovac, Alexey I. Gubinb, Vitaliy B. Krasovitskya, Alexander A. Lavrinovichb
aB. Verkin Institute for Low Temperature Physics & Engineering, Kharkov, 61103, Ukraine
bA. Usikov Institute for Radiophysics & Electronics, Kharkov, 61085, Ukraine
cInstitute for Single Crystals, Kharkov, 61001, Ukraine
Transport properties in a PLD La0.5Sr0.5CoO3-d film are studied by DC and microwave (41 GHz) technique. It is found that the microwave conductivity increases by the order of the magnitude at the transition to the ferromagnetic state. This is accompanied by only 10 % increase in the DC conductivity. This effect and the DC magnetoresistance data obtained are discussed considering the extrinsic and intrinsic sources of magnetic inhomogeneity in doped cobaltates, including the phase separation.
Structure and electromagnetic properties in thin films of Pr0.65Ca0.35MnO3
Masato Araia, Takahiro Nakayamaa, Osami Yanagisawab, Mitsuru Izumia
aLaboratory of Applied Physics, Tokyo University of Marcantile Marine, 2-1-6 Etchu-jima, Koto-ku, Tokyo 135-8533, Japan
bYuge National College of Maritime Technology, Yuge, Ochi-gun, Ehime 794-2593, Japan
We have studied the ESR on the photo-induced phase transition of Pr0.65Ca0.35MnO3 in the canted antiferromagnetic state 3. Presently we report the magnetic property of the thin film of Pr0.65Ca0.35MnO3 prepared with RF magnetron sputtering. Structurally, according to X-ray diffraction, high quality thin films were obtained on LaAlO3 substrate at 850 °C with Ar/O2 mixture gas atmosphere. They are ferrimagnet and the sample after long time deposition clearly shows the sign of charge-order formation. These properties are discussed comparatively with their bulk materials.
Fabrication of LBMO films and Magnetic Properties at Low Temperatures
Kouji Yoshii, Shin-ichi Iwasaki, Masaki Tada, Gufran Ahmad, Tamio Endo
Faculty of Engineering, Mie University, Tsu, Mie 514-8507, Japan
Thin films of (La,Ba)MnO3 were deposited by IBS at various substrate temperatures Ts and oxygen partial pressures Po. Magnetic properties were investigated in terms of SQUID, magnetoresistance and ferromagnetic resonance (FMR). The various samples were characterized by FMR at 77 K. Effective magnetization M of the samples deposited at Ts=750°C is larger for Po=1.5 than for 0.5 mTorr. Peak half width G is larger for 0.5 than for 1.5 mTorr, then the stronger magnetic and more homogenious film can be fabricated at 1.5 mTorr. G|| is larger than G^. After annealing, M is increased, and the magnitudes of M^ and M|| are converted to M^ > M||. The annealing affects seriously on in-plane and out-of-plane magnetization mproperties. The optimum annealing condition is 875°C ® 800°C to increase M^. The magnetic homogeneity can be remarkably improved by the annealing both for H|| and H^.
Temperature Dependence of FMR in La-Ba-Mn-O Thin Films
Shin-ichi Iwasaki, Masaki Tada, Jiro Yamada, Youichiro Inamori, Tamio Endo
Faculty of Engineering, Mie University, Tsu, Mie 514-8507, Japan
(La,Ba)MnO3 thin films were fabricated by IBS. Ferromagnetic resonance (FMR) was measured on as-deposited and annealed samples at various temperatures (T). The resonance fields Hr, peak half widths G and magnetizations M were obtained for H||plane and H^plane. The as-deposited film and the annealed film at 900 °C in O2 showed FMR from 77 K to TC=175 K and 185 K. In the annealed sample, Hr^ is larger than Hr|| at 77 K due to demagnetization. Hr^ decreases while Hr|| increases with increasing T, and finally they merge. M^ is larger than M||, and they decrease with increasing T. G|| is larger than G^, then spins are more distributed in H|| than in H^. G|| monotonically decreases with increasing T, then widely-distributed spins die out and only in-plane oriented spins are kept alive. While G^ once decreases then increases due to activated thermal fluctuation of remnant spins.
Field Induced Magneticstructure Transisiton of LaSrFeO4
Hirofumi Kawanakaa, Hiroshi Bandoa, Kazuyoshi Mitsugia, Akifumi Sasaharab, Yoshikazu Nishiharab
aNational Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568, Japan
bFaculty of Science, Ibaraki University, Mito, Ibaraki 310-8512, Japan
We report the magnetic transition studies on LaSrFeO4. Single crystal of LaSrFeO4 prepared by the floating-zone method and investigated by resistivity, magnetic susceptibility, and Mössbauer effect measurements. The crystal structure of LaSrFeO4 is K2NiF4-type tetragonal (I4/mmm) symmetry. LaSrFeO4 is a Mott-type antiferromagnetic semiconductor with multi phase transition. The Mössbauer spectra at room temperature consist of a single Fe3+ hyperfine sextets which are evidence for magnetically ordered phase. Furthermore we found the spin flop at 1.8 Tesla, T = 5 K in magnetization process, and make clear the magnetic ground state has [1 1 0] and [-1 1 0] direction spin order in the c plane.
Non-linear conduction in the charge-disportionated phase of La1/3Sr2/3FeO3
Noriya Ichikawa, Masamichi Yamamoto, Takahito Terashima, Mikio Takano
Institute for Chemical Research, Kyoto University, 611-0011, Gokasho, Uji, Kyoto-Fu, JAPAN
In the perovskite La1/3Sr2/3FeO3 charge disproportionation (CD) occurs at 200K: 3Fe[ 11/3]+®2Fe3++Fe5+. Various studies indicate that in the CD phase there exist layered spin and charge order stacking along [111]cubic direction, which can be regarded as a coupled spin density wave (SDW) and charge density wave (CDW). To investigate the nature of the CDW, we measured resistivity at pulsed high electric field up to 2000V/cm; special care was taken to eliminate the self-heating effect by choosing the thin film sample and by micro-fabrication with the focused ion beam technique. Current-voltage characteristics showed non-linear behavior (above 1000V/cm at 170K) only in CD phase and the threshold field Eth increases as temperature is reduced. Other phenomena for depinned CDW like negative differential resistivity and delay in pulse wave form were also observed. These suggest a collective motion in the present system.
Specific Heat Studies on the Charge and Magnetic Ordering in Manganites
H. D. Yanga, H. L. Huanga, P. L. Hoa, W. L. Huanga, C. W. Huanga, S. J. Liub, J. Y. Linc
aDepartment of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan, ROC
bDepartment of Electrophysics, National Chiao-Tung University, Hsin-Chu 300, Taiwan, ROC
cInstitute of Physics, National Chiao-Tung University, Hsin-Chu 300, Taiwan, ROC
Specific heat studies with a wide range of temperatures (T=30 - 300 K) on manganites Pr0.65Ca0.25Sr0.1MnO3 (PCSMO) and Nd0.125Sm0.375Sr0.5MnO3 (NSSMO) are reported. Both CO and AFM transitions in PCSMO and NSSMO can be clearly observed in specific heat data. However, the specific heat anomaly associated with the ferromagnetic (FM) ordering transition, which is usually corresponding to the MI transition, in both materials is not definitely determined. The possible explanations are discussed on the basis of whether the FM ordering is metastable or not.
Pressure induced ferromagnetic metal for a Mott insulator Ca2RuO4
F. Nakamuraa, T. Gokoa, M. Itoa, T. Suzukia, T. Fujitaa, S. Nakatsujib, H. Fukazawab, Y. Maenob, P. Alirezac, S.R. Julianc
aADSM, Hiroshima University, Higashi-Hiroshima 739-8530 Japan
bDepartment of Physics, Kyoto University, Kyoto 606-8502, Japan
cCavendish Laboratory, University of Cambridge, Cambridge, UK
We found a Mott insulator Ca2RuO4 features a metal-insulator transition at P ~ 0.5 GPa: at 300K from paramagnetic insulator to paramagnetic quasi-2D metal; at T £ 12K from AFM insulator to FM 3D metal. The P-phase diagram, especially the itinerant FM, is quite unique to our knowledge. We discuss the importance of structural distortions, which are expected to couple strongly to P. Moreover, our results suggest the induction of a FM quantum critical point at P £ 10GPa. We have strong interest in the connection between the p-wave superconductor Sr2RuO4, and the FM of metallic Ca2RuO4.
Crystal Structures and Magnetic Properties of the Double Perovskite
(Ca2-2xSr2x)FeMoO6
J. B. Shia, Y. Y. Fana, P. H. Penga, F. C. Joua, C. Y. Leea, H. C. Kub, S. L. Youngc, H. Z. Chenc
aDepartment of Electronic Engineering, Feng-Chia University, Taichung 407, Taiwan.
bDepartment of Physics, National Tsing Hua University, Hsinchu 300, Taiwan.
cDepartment of Electrical Engineering, Shiuping Institute of Technology, Taichung 412, Taiwan.
Chemical size effect on structural and magnetic properties in (Ca2-2xSr2x)FeMoO6 has been examined. The compounds crystallize in the monoclinic system for 0.0 £ x < 0.2, the orthorhombic for 0.2 £ x < 0.4 and the tetragonal for 0.4 £ x. The Curie temperature TC increases with increasing x from 318 K (x=0.0) to 393 K (x=1.0). At 82 K, the saturation magnetization of all samples remains MS £ 3.5mB/formula unit compared to a theoretical spin-only moment 4mB/formula unit for a perfectly ordered compound. This discrepancy is probably due to a slight disorder and valence-fluctuation between the Fe and Mo atoms.
Structure and magnetic properties of BaFeO3-d studied by neutron scattering measurements
Kazuhiro Moria, Takashi Kamiyamaa, Hisao Kobayashib, Toshiya Otomoa, Susumu Ikedaa
aInstitute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan
bDepartment of Physics, Tohoku University, Sendai, Miyagi 980-8578, Japan
It is reported that BaFeO3-d with an average oxidation state of +4 shows a decrease of Fe4+ concentration at low temperature, from a result of Mössbauer measurements. It implies that a charge disproportionation of Fe4+, 2Fe4+ ® Fe3+ + Fe5+, occurs in this system. In this work, we have investigated the structure and the magnetic properties of BaFeO3-d using neutron scattering measurements. A drastic distortion of [FeO6] octahedra is observed around 180 K. The occurrence of the drastic distortion agrees well with the result of Mössbauer measurements.
Charge and Orbital Ordered States in Nd1-xSr1+xMnO4 (x=0.67, 0.75)
Hironori Nakaoa, Tadashi Satoha, Junko Satoha, Youichi Murakamia, Masato Kubotab, Tsuyoshi Kimurac, Yoshinori Tokurac
aDepartment of Physics, Tohoku University, Sendai 980-8578, Japan
bPhoton Factory, Institute of Materials Structure Science, KEK, Ibaraki 305-0801, Japan
cDepartment of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
The charge and orbital ordered states in the single-layered manganite crystals, Nd1-xSr1+xMnO4 (x=0.67, 0.75), have been investigated. We have observed the superlattice spots of wave vector with q=(d,d,0), d ~ [ 1/6] ([ 1/8]) in x=0.67 (x=0.75) by non-resonant x-ray scattering, which indicate atomic displacements induced by the charge-orbital ordering. To distinguish the charge-orbital states of Wigner-crystal and bi-stripe models, the resonant x-ray scattering technique were utilized at the q positions.
mSR Study of Magnetic Order in Sr2Ru1-xTixO4
G.M. Lukea, M.T. Roversa, P.P. Kyriakoua, I.M. Gatb, M.I. Larkinb, A.T. Savicib, Y.J. Uemurab, K.M. Kojimac, N. Kikugawad, Y. Maenoe
aDept. of Physics & Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1, Canada
bDept. of Physics, Columbia University, New York, NY 10027, USA
cDept. of Advanced Materials Science, University of Tokyo, Bunkyo-ku, Tokyo 113-7656, Japan.
dDept. of Physics and Venture Business Lab., Kyoto University, Kyoto 606-8502, Japan
eDept. of Physics and International Innovation Center, Kyoto University, Kyoto 606-8502, Japan
Sr2RuO4 is an unconventional superconductor with Tc=1.5 K which is extremely sensitive to even non-magnetic impurities. We have performed muon spin relaxation (mSR) measurements of Sr2Ru1-xTixO4. For x=0.01, 0.03 we observe weak dilute spin freezing, similar to that seen in nominally pure but non-superconducting Sr2RuO4 while with x=0.09 we observe spin glass freezing below Tg » 15 K.
Electronic Transport of Bilayer Manganite La1.2Sr1.8Mn2O7 Single Crystal
C. C. Almasana, X. J. Chena, C. L. Zhanga, J. S. Gardnerb, J. L. Sarraob
aDepartment of Physics, Kent State University, Kent OH 44242, USA
bLos Alamos National Laboratory, Los Alamos NM 87545, USA
We report magnetoresistivity measurements on a La1.2Sr1.8Mn2O7 single crystal. The charge transport in the ferromagnetic phase is dominated by two-magnon scattering in the high T range and by weak localization effects at lower T, in the non-metallic regime. In the paramagnetic phase, rab(T) obeys the adiabatic small polaron hopping mechanism, while rc(T) follows an Arrhenius behavior with the same activation energy. Considering the magnetic character of the polarons and the presence of ferromagnetic clusters in the paramagnetic state, we developed a model to determine rab,c(H,T). The excellent agreement between calculated and measured rab,c(H,T) indicates that small polarons play an essential role in the electrical transport of the paramagnetic phase of bilayer manganites.
EPR and magnetization study of the Ni2FeV3O11 vanadate
Nikolaos Guskosa, V. Likodimosb, M. Wabiac, S. Glenisa, J. Typekc, S. K. Patapisa, A. Blonska-Taberod, I. Rychlowska-Himmeld, M. Kurzawad, C.L. Line
aSolid State Section, Department of Physics, University of Athens, Panepistimiopolis, 15784 Zografos, Athens, Greece
bDepartment of Physics, National Technical University, 15780 Athens, Greece
cInstitute of Physics, Technical University of Szczecin, Al.Piastow 17, 70310 Szczecin, Poland
dInstitute of Chemistry and Environmental Protection, Technical University of Szczecin, Al.Piastow 42, 71065 Szczecin, Poland
eDepartment of Physics, Temple University, Philadelphia, PA 19122 USA
The novel nickel-iron vanadium oxide Ni2FeV3O11 is investigated by EPR and dc magnetization measurements. Both measurements exhibit several singularities, indicative of diverse magnetic interactions.
Charge Disproportionation of A site in New Ni(II) Perovskite BiNiO3
Shintaro Ishiwataa, Masaki Azumab, Mikio Takanoa, Eiji Nishiboric, Masaki Takatac, Makoto Sakatac
aInstitute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto, Japan
bICR, Kyoto Univ. and PRESTO-JST, Kawaguchi, Saitama, Japan
cSchool of Engeneering, Nagoya University, Furo-cho, Chigusa-ku, Nagoya, Aichi, Japan
A new triclinic perovskite BiNiO3 was synthesized at a high pressure of 6.5 GPa in an oxidizing atmosphere. Structure refinements based on synchrotron X-ray powder diffraction and bond valence calculation revealed a disproportionation of the Bi ions into Bi3+ and Bi5+, both being located in distorted oxygen octahedra. Because of the presence of Bi5+, the oxidation state of Ni was 2+, rather than 3+ as had been expected, and BiNiO3 thus showed insulating behavior with localized spins of S=1. An antiferromagnetic ordering with spin canting took place at 300K.
MAGIC HOLE DOPED COMPOSITION OF Sm1-xSrxMnO3 MANGANITE: CRYSTAL STRUCTURE, AND UNUSUAL MAGNETIC AND TRANSPORT PROPERTIES AT x= 0.45
A. V. Lazutaa, V. A. Ryzhova, A. I. Kurbakova, V. A. Trounova, I. I. Larionova, C. Martinb, B. Raveaub
aPetersburg Nuclear Physics Institute, Gatchina 188350 St.Petersburg, Russia
bLaboratoire Crismat, Ismra, Boulevard du Mal Juin, 140050 Caen Cedex, France
The manganite is established to exhibit a Pbnm space group and the net ferromagnetic (F )ground state, with Jahn-Teller distortions remaining in metallic F phase below Tc. A field hysteresis of the second harmonic of magnetization is observed above Tc. This behavior is explained by assuming a spontaneous magnetization to be associated with the AF domains possessing a weak F. The ordered regions destroy at Tc that indicates unusual character of the transition whose possible scenarios are discussed.
NONLINEAR MAGNETIC PROPERTIES OF Nd0.77Ba0.23MnO3 PSEUDOCUBIC SINGLE CRYSTAL IN CRITICAL PARAMAGNETIC REGION AND PHASE SEPARATION
A. V. Lazutaa, V. A. Ryzhova, I. D. Luzyanina, V. P. Khavronina, I. I. Larionova, I. O. Troyanchukb, D. D. Khalyavinb
aPetersburg Nuclear Physics Institute, Gatchina 188350 St.Petersburg, Russia
bInstityte of Physics of Solids and Semiconductiors, N.A.S., P.Brovki 17, 220072, Minsk, Belarus
The second harmonic of magnetization is studied for Nd0.77Ba0.23MnO3 that exhibits the insulating ferromagnetic ground state. The nonlinear response reveals the coexistence of the two magnetic phases in the paramagnetic region below Tp = 147K. Above Tp , critical behavior is described by dynamic scaling for the 3-D isotropic ferromagnets. The appearance a new magnetic phase is attributed to phase separation which can occur at orbital ordering in the cubic manganites.
Elastic and structural properties of single crystalline La0.95Sr2.05Mn2O7
Yuji Kodama, Yoshiki Nakanishi, Noriyuki Yoshimoto, Masahito Yoshizawa
Department of Materials Science and Engineering , Iwate University, Morioka 020-8551, Japan
It has been reported that CE-type Charge-ordered (CO) phase is observed at TCO = 210 K 4 and the phase competition between this phase and A-type antiferromagnetic phase below TCO in LaSr2Mn2O7 5, which is a half-doped bilayered manganaite La2-2xSr1+2xMn2O7 with x = 0.5. The competition becomes stronger in x =0.525 sample. We have grown single crystals of x = 0.525 by an optical floating-zone furnace to measure some physical and structual properties. We will discuss the results of ultrasonic measurement and the origin of the pase competition by comparing to the results for LaSr2Mn2O7 6.
Magnetic phase diagram of (La1-zPrz)1.2Sr1.8Mn2O7 for z = 0.6
Y. Nakanishia, K. Shimomuraa, M. Matsukawaa, S. Nakamurab, R. Suryanarayananc, A. Revcolevschic, M. Yoshizawaa
aDepartment of Materials Science and Engineering , Iwate University, Morioka 020-8551, Japan
bCenter for Low Temperature Science, Tohoku University, Sendai 980-8577 Japan.
cLaboratoire de Chimie des Solide, CNRS, Universite Paris-Sud, 91405 Orsay, France.
We have established a magnetic phase diagram of (La1-zPrz)1.2Sr1.8Mn2O7 for z = 0.6 by means of elastic constants and magnetization measurements. A metamagnetic transition at Hm was observed both with a large hysteresis below the temperature of T* ~ 40 K, and without a hysteresis above T*. Two distinct elastic anomalies were observed in the field-dependence of elastic constants at the corresponding field Hm and another one below T*. It was found that there were mainly three magnetic phases in the Field-Temperature (H-T) phase diagram. We will discuss the magnetic properties at low temperatures.
Electronic Properties of the Novel 4d Metallic Oxides SrRhO3 and Sr3Rh2O7
Kazunari Yamauraa, Qingzhen Huangb, Masao Araia, David P. Youngc, Eiji Takayama-Muromachia
aNational Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
bNIST Center for Neutron Research, 100 Bureau Dr., Gaithersburg, MD 20899, USA
cDepartment of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA
The title metallic compounds (both have five 4d electrons per Rh) with perovskite- and Ruddlesden-Popper-type structures have been synthesized recently in our group by applying high-pressure and high-temperature techniques (6 GPa and 1500 °C), followed by measurements of the magnetic susceptibility, electrical resistivity, thermopower, and specific heat. Neutron and x-ray diffraction studies at room temperature revealed those structures. The DOS of SrRhO3 was computed by LDA method with and without consideration of spin polarization. The electronic properties of these compounds will be reviewed, and compared with those of the analogous ruthenates, which have received the most attention.
The comparison of structure and magnetic properities between La1-xPbxMnO3 and La1-xPbxCoO3 system
Y. L. Hsieh, M. F. Tai
Dep. of Physics, National Chung Cheng University, Ming-Siung, Chia-Yi 621, Taiwan
The perovskite-like hole-doped La1-xPbxTO3 (x=0-0.5) oxides with T = Mn and Co are in the rhombhedral R[`3]c structure. The similar physical phenomena, including the M-I transition, CMR, and related striking magnetostructural properties etc., have been observed in both the strongly correlation electron systems, however, the fundamental mechanisms actually are different. All our maganese samples exhibit long-range order ferromagnetism , and the cobalt compounds present spin-glass behavior, or even paramagnetism above 2 K.
Optical Study in the Charge-Ordered Phase of (Nd1-xSrx)MnO3
Haruhiko Kuroe, Ikue Habu, Akihiko Sakuta, Hideki Kuwahara, Tomoyuki Sekine
Department of Physics, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan
We report the temperature and Sr concentration dependences of Raman and infrared reflection spectra in (Nd1-xSrx)MnO3. When x = 0.5, a phase transition from the paramagnetic insulator phase to the ferromagnetic metal one occurs at 250 K and a successive phase transition to the antiferromagnetic charge-ordered one at TCO = 158 K. Above TCO, we observe a broad Raman peak around 200 cm-1, consistent with the Ibmm symmetry with a small lattice distortion from the ideal perovskite structure. Below TCO, we observe several new Raman peaks, coming from the folded phonons due to the formation of the superlattice. The infrared reflection spectra support the existence of the folded phonons below TCO. A magnetic Raman peak from the single-ion-anisotropy gap is also observed below TCO. These new peaks are not observed in the x = 0.48 sample which does not have the charge-ordered phase.
High Field and Low Temperature X-ray Study on Phase Segregation for Nd0.5Sr0.5MnO3 Powder and Single Crystal
Satoshi Awajia, Yosuke Watanabeb, Tetsutaro Masakib, Manabu Fujiwarab, Tetsuo Fukaseb, Norio Kobayashib, Kazuo Watanabea
aHFLSM, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
bInstitute for Materials Research, Tohoku University, Sendai 980-8577, Japan
It has been found that the coexistence of the high temperature ferromagnetic (FM) and the low temperature antiferomagnetic (AF) phases was observed below the charge order transition temperature Tco for the Nd0.5Sr0.5MnO3 powder sample. In order to investigate details of the phase segregation, the X-ray diffraction was carried out for the Nd0.5Sr0.5MnO3 single crystal in magnetic fields up to 5 T. It was found that the phase segregation is strongly depends on the wave length of X-ray. These results suggest that the phase segregation of FM and AF mainly occurs near the surface within a few mm in depth .
On the ferromagnetism of high-spin states
Nadejda V. Terekhinaa, Julia Mikhailovaa, Rogdai Zaitsevb
aNII Teplopribor, Prospect Mira 95, Moskow 129 085, 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.
Co K-edge Pre-edge XANES Studies on Intermediate Spin State of RCoO3 (R = La, Eu)
J. Y. Chang, B. N. Lin, Y. Y. Hsu, H. C. Ku
Department of Physics, National Tsing Hua University, Hsinchu, Taiwan 300, R.O.C.
Room temperature Co K-edge x-ray absorption near-edge spectra (XANES) for the rhombohedral RCoO3 (R = La, Eu) are reported. The small pre-edge peaks (P) observed near 7707-7715 eV are from the 1s-3d dipole transition, which is weakly allowed through the hybridization of Co 4p states with Co 3d states of neighboring atoms. The appearance of more than one pre-edge peak indicates an absorption transition to the majority eg states as well as to minority eg and t2g state, which support a spin state transition from low spin state (LS: t2g6) to intermediate spin state (IS: t2g5eg1) around 90 K for LaCoO3. Similar pre-edge features are observed for EuCoO3 indicates that Eu compound is also in the IS state with higher spin state transition temperature close to room temperature.
2D Ferromagnetic Fluctuation above TN in Orbital-ordered LaMnO3 A-type Antiferromagnet
C. T. Chen, S. H. Wu, Y. Y. Hsu, B. N. Lin, H. C. Ku
Department of Physics, National Tsing Hua University, Hsinchu, Taiwan 300, R.O.C.
Onset of two-dimensional (2D) ferromagnetic short range order with T2D = 152 K was observed above A-type antiferromagnetic (AF) N\acute eel temperature TN = 139 K in orbital-ordered LaMnO3 Mott insulator, using low field ( £ 10 mT) field-cooled (FC) and zero-field-cooled (ZFC) magnetic susceptibility measurements. The A-type AF order with strong basal plane ferromagnetic coupling is due to orbital-ordered Mn3+ eg electrons at Too @ 780 K, and AF structure is stabilized through weak c-axis t2g antiferromagnetic coupling. For applied field of 0.1 T, T2D = 147 K and TN = 137 K. Low temperature magnetization and Mn K-edge x-ray absorption near-edge spectrum (XANES) data on orthorhombic LaMnO3 and rhombohedral LaMnO3+d (d > 0) will be discussed.
Transport Properties and Magnetic Phase Diagram in a Strongly Correlated La0.7(Ba1-xPbx)0.3MnO3+d perovskites
M. F. Tai, S. Z. Gong, Y. S. Wang
Department of Physics, Chung Cheng University, Chia-Yi, Taiwan 621, R.O.C.
The crystallographic data, transport properties and magnetic phase diagrams have been investigated for strongly electron correlated La0.7(Ba1-xPbx)0.3MnO3+d (0.0 £ x £ 1.0) series. All our samples are in a rhombohedral structure of lattice parameters a @ 5.50 Å and c @ 13.38 Å. The enhanced disorder effect of addition of the Pb2+ ions doesn't apparently affect on both the metal-insulating and magnetic ordering temperatures as well as the magnetoresistance (MR) ratio. For the MR ratios of all samples linearly decrease with temperature from @ 25 % at 5 K down to @ 6 % at 300 K. The chemical disorder effect of the Pb substitution doesn't change the magnetic properties at low temperatures. It can be contributed to exhibit the same ratios of [Ba2+]+[Pb2+]/[La3+] and [Mn4+]/[Mn3+] in the Pb doping manganese oxides.
Raman Scattering Study of Y1-xCaxTiO3 Single Crystals
Takao Tsuruia, Norio Ogitab, Masayuki Udagawab, Masami Tsubotac, Kazuyuki Uchihirac, Fumitoshi Igac
aVenture Business Laboratory, Hiroshima University, Higashi-Hiroshima, 739-8527 Japan
bFaculty of Integrated Arts & Sciences, Hiroshima University, Higashi-Hiroshima, 739-8521 Japan
cADSM, Hiroshima University, Higashi-Hiroshima, 739-8530 Japan
We have systematically studied the Raman scattering spectra of single crystal Y1-xCaxTiO3 in the temperature region from 298K to 8K. The observed peaks below 600cm-1 have been assigned as phonons, and their observed number satisfies the symmetry of Pbnm at room temperature. However, new additional peaks appear below 200K. This result shows that the crystal structure becomes monoclinic of P21/n. This structural phase transition from orthorhombic to monoclinic ones universally occurs for x £ 0.39 at around 200K.
Dynamics of Phase Transitions in Cobalt Perovskites
Despina Louca
University of Virginia, Department of Physics, Charlottesville, VA 22903
La1-xSrxCoO3 is distinct because of its unique spin transitions, subjecting the system to variable spin-lattice coupling. These occur with increasing temperature and doping from the low spin, to either a high-spin or an intermediate-spin (IS) configuration. The IS state is distinct because it is Jahn-Teller (JT) active. Such spin fluctuations would be accompanied by distortions in the local atomic structure corresponding to the type of transition. Pair density function analysis provided strong evidence for local lattice distortions associated with a Jahn-Teller active mode directly correlated to the change in the magnetic/conductive states of this system. Measurements of S( Q,w) provided additional evidence that lattice modes indeed change with temperature and composition. The magnitude of their intensity is indicative of a collective excitation consistent with a phase transition not otherwise observed macroscopically.
Pressure Effect on Transport and Magnetic Properties of A2FeMoO\bm6 (A = Ba, Sr)
Tatsuo Gokoa, Eiji Morimotoa, Yoshiyuki Endoa, Juichiro Araia, Takehiko Matsumotob
aDepartment of Physics, Tokyo University of Science, Noda, Chiba 278-8510, Japan
bNational Institute for Material Science, Tsukuba, Ibaraki 305-0047, Japan
For double perovskite oxides A2FeMoO6 (A= Ba, Sr), which show the colossal magnetoresistance up to room temperature, the resistivity and magnetization have been measured under pressure and magnetic fields. As pressure is applied to Ba2FeMoO6 (BFMO), the magnetic transition temperature TC increases linearly, suggesting the enhancement of magnetic interactions between cations. The normalized resistivity r(P)/r(P=0) at 5 K exhibits quite same pressure dependence in all magnetic fields up to 7 T, though the field dependence of magnetoresistance is extremely different in each magnetic field. This result indicates that the components contributing to the large filed-dependence of r hardly depends on pressure.
Pressure-enhanced antiferromagnetism in Sr3Ru2O7
Yuri Sushko, Bruno deHarak, Gang Cao, Oleg Naumenko
Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506
The experimental picture of magnetism in a double-layered ruthenate Sr3Ru2O7 (with both the ferromagnetic and antiferromagnetic correlations present) could be consistent with a FM (itinerant) ordering of spins within bilayers, and AF (superexchange) coupling between bilayers. Since the effects of reduced dimensionality can be suppressed by pressure, we have conducted the systematic study of the effects of hydrostatic (helium-gas) pressure on magnetic susceptibility of single crystals of Sr3Ru2O7. Here we report that indeed the tendency to antiferromagnetism (and not ferromagnetism) is enhanced under hydrostatic pressure, as evidenced by an observed increase with pressure of a Neel-like transition temperature Tmax. We also report a pressure-induced first-order transition, presumably a structural one, which occurs at around 80K in response to the change of pressure at low temperature.
Study of low band width manganites with equal average ionic radii and manganese valence ratio
Subhayan Biswasa, Sandip Chatterjeeb, A. K Nigamb, S. K Dea
aDept. of Materials Science, Indian Association for the Cultivation of Science, Kolkata, India,700032
bTata Institute of Fundamental Research, Homi Bhabha Road, Mumbai, India, 400005
The reason for the interesting properties observed in CMR materials, other than average ionic radii ( < rA > ) and Mn valence ratio (Mn3+/Mn4+), has been tried to find out by investigating the transport and magnetic properties of Pr0.65(Ca0.7Sr0.3)0.35MnO3, Pr0.527La0.123(Ca0.8Sr0.2)0.35MnO3 and Pr0.65(Ca0.866Ba0.134)0.35MnO3. The < rA > and valence ratio of all three samples have been kept equal. The out come of the investigation indicates more intense role of the nature of individual A-site cation and the lattice mismatch.
ESR INVESTIGATION OF Nd0.77Ba0.23MnO3 SINGLE CRYSTAL IN PARAMAGNETIC REGION: EVIDENCE FOR PHASE SEPARATION
A. V. Lazuta, V. A. Ryzhov, I. A. Kiselev
Petersburg Nuclear Physics Institute, Gatchina 188350 St.Petersburg, Russia
We present an electron-spin-resonance (ESR) study in single crystal of Nd0.77Ba0.23MnO3 above the Curie point Tc =124K. The temperature dependence of the ESR linewidth is established to agree well with critical behavior of that for a 3-D isotropic ferromagnet in paramagnetic region above Tp = 147K, when relaxation of an uniform magnetization is caused by the dipolar interactions and spin-phonon coupling. Below Tp a new regime is observed, the signal depending on a temperature treatment. The compound reveals the two signals at a slow cooling from the room temperature. This effect is assumed to be related to phase separation that can occur in the cubic manganites at orbital ordering.
Spectroscopic Evidence for Charge-Density-Wave Formation in Manganite
Noriaki Kida, Masayoshi Tonouchi
Research Center for Superconductor Photonics, Osaka University, Suita, Osaka 565-0871, Japan.
The typical charge ordered manganite, Pr0.7Ca0.3MnO3 investigated here, shows the charge ordering (CO), which is characterized both by a single-particle excitation across the charge-gap 2D and by a collective excitation well below 2D. The former spectrum has been extensively investigated in recent years. However, a clear evidence for the presence of the collective excitation has not been reported so far. Here we used THz time-domain spectroscopy to directly probe the low-energy (0.5-5 meV) electrodynamics of Pr0.7Ca0.3MnO3 and revealed the existence of a finite peak structure around 2-3 meV well below 2D ~ 300 meV. As compared to the optical properties of low-dimensional materials, we attributed this observed structure to the collective excitation mode arising from the charge-density-wave condensate.
Successive Transitions of the Ordered REBaMn2O6 RE=Tb, Dy , Ho and Y
T. Nakajimaa, H. Kageyamaa, H. Yoshizawab, M. Ichiharaa, K. Ohoyamac, Y. Uedaa
aMaterials Design and Characterization Laboratory,ISSP,University of Tokyo,Kashiwa,Chiba 277-8581,Japan
bNeutron Scattering Laboratory, ISSP, University of Tokyo, Tokai, Ibaraki 319-1106, Japan
cInstitute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
The ordered perovskites REBaMn2O6 (RE=Tb, Dy, Ho and Y) consist of alternate stack of the RE3+ and Ba2+ ions along the c-axis. The YBaMn2O6 shows three successive transitions, a structural transition (Tc1=520 K), a M-I transition (Tc2=480 K) and an antiferromagnetic transition (Tc3=195 K). The TbBaMn2O6, the DyBaMn2O6 and the HoBaMn2O6 show the similar transitions as the YBaMn2O6. It should be noticed that the charge/orbital order in these compounds occurs at much higher temperature compared with the other disordered manganite perovskites. We will discuss these phase transitions from the crystal structure.
Optical Reflectivity Study on Magnetoresistive Manganese Perovskites:
Impurity Effect on the Ferromagnetic-Metallic and Charge-Ordered States
Shunsuke Okuyama, Koshi Takenaka, Ryozo Shiozaki, Yuko Sawaki, Shunji Sugai
Department of Physics, Nagoya University, 464-8602 Nagoya, Japan
Impurity effect on manganese perovskites are investigated by the optical reflectivity measured on cleaved surfaces of the single crystals. The Al impurity affects optical conductivity s(w) of ferromagnetic-metallic La1-xSrxMnO3 over a wide energy range up to 1 eV or higher, contrary to the simple-Drude picture. In particular, the Al impurity induces the unconventional localization state, which is characterized by the additional absorption at ~ 3 eV in s(w) in addition to the infrared peak. The present study shows that the energy gap of the charge-ordered (CO) state in Nd0.5Sr0.5MnO3 is about 0.5 eV, much larger than that suggested by the previous studies using polished surfaces. The CO state can be easily damaged by external disorder. We also discuss the different effect on the CO state between Cr and Al doping.
Spin modulation of 57Fe NMR frequency and relaxation in BiFeO3
D.F. Khozeeva, A.V. Zalesskyb, A.A. Gippiusa, E.N. Morozovaa, A.A. Bushc, V.S. Pokatilovc
aMoscow State University, 119899, Moscow, Russia
bInstitute of Crystallography, RAS, Leninskii pr. 59, 117333, Moscow, Russia
cMoscow State Technical University of Radioengineering, Vernadskogo pr.78, 117454, Moscow, Russia
NMR spectra were measured in 57Fe enriched ferroelectric-antiferromagnet BiFeO3 with space modulated magnetic structure of cycloidal type. This structure leads to space modulation of local field on 57Fe nuclei as well as space periodic spin-spin relaxation and specific NMR line shape with frequency variable local width. Line shape temperature behavior is described using the model of nuclei in Bloch walls. This effect is based on indirect Sule-Nakamura spin-spin interaction which becomes effective at high concentration of magneto-active nuclei as a consequence of excitement of spin waves.
Phase Diagram and Magneto-Transport Properties in Nd1-xSrxMnO3 Crystals
H. Kuwaharaab, R. Kawasakia, Y. Hirobea, S. Kodamaa, A. Kakishimaa
aDept. of Phys., Sophia Univ., Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan
bPRESTO, JST, Tokyo 102-0074, Japan
We have investigated electronic transport and magnetic properties of Nd1-xSrxMnO3 crystals with controlled band filling (0 £ x £ 0.8) grown by the floating zone method. The phase diagram of Nd1-xSrxMnO3 was obtained through magnetization, resistivity, and crystal structure measurements. We have found the phase separation near the phase boundary (x=0.62) between the A-type-antiferromagnetic (AF) metal with monoclinic symmetry and the C-type-AF insulator with tetragonal one. We have also studied magnetoresistance (MR), Hall resistivity, and Seebeck coefficient in the samples showing various electronic and magnetic structures. We have observed a large positive MR just below TN in the A-type-AF sample (x=0.60), which is not the conventional negative CMR near TC in manganites.
Studies of La0.7-xPrxCa0.3MnO3 (x=0.4 and 0.5) under pressure and magnetic field
Seongsu LEEa, J.-G. Parka, H.C. Kimb
aDepartment of Physics, Sung Kyun Kwan University, Suwon 440-746, Korea
bMaterial Science Laboratory, Korea Basic Science Institute, Taejeon 305-333, Korea
We investigated resistivity of La0.7-xPrxCa0.3MnO3 (x=0.4 and 0.5) polycrystals under hydrostatic pressures and magnetic fields. With increasing pressures and fields, overall resistivity values drop sharply and at the same time MI transition increases monotonically. With increasing pressures and fields, however, our resistivity data show another anomaly developing at lower temperature than the MI transition. But, our susceptibility data do not show any anomalous behavior at the temperature of the resistivity anomaly, suggesting that this new feature seen in the resistivity data is unlikely to be connected to a change in the thermodynamic properties.
Inhomogeneous States and Isotope Substitution in Magnetic Oxides
N.A. Babushkina
Institute of Molecular Physics, RRC ``Kurchatov Institute'', 123182 Moscow, Russia
Inhomogeneous states and the phase separation originating from the competition between various types of charge, spin, and orbital ordering in complex magnetic oxides were experimentally studied. The oxygen isotope substitution was used both as the unique tool for investigating inhomogeneous state and as the method for modification of the ground state. At first, we demonstrate that the magnetic and transport measurements revealed a phase separation in (La0.25Pr0.75)0.7Ca0.3MnO3 compound with various concentrations of 18O. Then we studied the isotope effect on transport and magnetic properties of Sm0.55Sr0.45MnO3 manganite and showed that the 16O ® 18O isotope substitution induces the phase separation in Sm0.55Sr0.45MnO3 system causes the formation of antiferromagnetic clusters in the ferromagnetic matrix.
Anomalies of magnetic and magnetoelastic properties in Nd1-xCaxMnO3
Kamil I. Kamilova, Antonina M. Kadomtsevaa, Yurii F. Popova, Gennadiy P. Vorob'eva, Jaroslav S. Shtoficha, Alexandr A. Mukhin b, Vsevolod Yu. Ivanovb, A. M. Balbashovc
aMoscow State University, Leninskie Gori, 119899 Moscow, Russia
bGeneral Physics Institute of the Russian Acad. Sci., 38 Vavilov St., 119991 Moscow, Russia
cMoscow Power Engineering Institute, 14 Krasnokazarmennaya St., 105835 Moscow, Russia
Magnetic, anisotropic, and magnetoelastic properties have been investigated for Nd1-xCaxMnO3 monocrystals (x=0; 0.25; 0.05; 0.3) in pulsed magnetic fields up to 250 kOe in temperature range 10-100 K. Jumps of magnetization and magnetostriction induced by the strong magnetic field H along b have been observed at Happrox100 kOe in the x=0, 0.25, 0.05 compounds. We attribute this phenomena to a reorientation of the weak ferromagnetic moment from c to b-axis. Corresponding H-T phase diagrams were obtained. This work supported by RFBR (00-02-16500 and 00-15-96695).
Induced by magnetic field spin reorientation in YMn2O5
Kamil I. Kamilova, Antonina M. Kadomtsevaa, Yurii F. Popova, Gennadiy P. Vorob'eva, Pavel.N. Makhova, Mohammad M. Tehranchib
aMoscow State University, Leninskie Gori, 119899 Moscow, Russia
bDepartment of Physics, Shahid Beheshti University, Evin, 19834 Teheran, Iran
In ferroelectric YMn2O5 weak ferromagnetism was found along a-axis of rhombic crystal. It was shown that the nature of ferromagnetic sublattices cant is determined by magnetoelectric ordering. Reorientation of magnetic moment was observed under strong magnetic field applied along b-axis of crystal, that was accompanied by sharp increase of magnetostriction and jumps of electric polarization. In EuMn2O5, as in YMn2O5, spontaneous and magnetic field induced phase transitions from incommensurate to commensurate phase were observed, accompanied by cardinal changing of magnetoelectrical properties.
This work supported by RFBR (01-02-16468 and 00-15-96695)
Orbital Order in La0.95Sr0.05MnO3 and LaMn1-xCrxMnO3 probed by ESR
J. Deisenhofera, H.-A. Krug von Niddaa, M.V. Ereminb, B.I. Kochelaevb, A. Loidla
aExperimentalphysik V, EKM, Institut für Physik, Universität Augsburg, D-86135 Augsburg, Germany
bKazan State University, 420008 Kazan, Russia
We present an analysis of Dzyaloshinsky-Moriya interaction and crystal-field parameters using the angular and T-dependence of the paramagnetic resonance shift and linewidth in single crystals of La0.95Sr0.05MnO3 within the Jahn-Teller distorted phase. The DM interaction ( ~ 1 K) results from the tilting of the MnO6 octahedra. The CF parameters D and E are found to be of comparable magnitude ( ~ 1 K) with D » -E. This indicates a mixing of the |3z2-r2ñ and |x2-y2ñ states for the real orbital order with an orbital parameter q » -60°. Thus, the discrepancy between anisotropic optical spectra and the value q » 108° obtained from neutron scattering in LaMnO3 can be explained. By substituting Mn with Cr, the JT-driven OO persists up to x=0.3. The Cr3+ ions do not contribute to the ESR signal.
GW Study of Half-Metallic Electronic Structure of La0.7Ba0.3MnO3
Hiori Kinoa, Ferdi Aryasetiawanb, Takashi Miyakec, Kiyoyuki Terakurab, Takahisa Ohnoa
aNational Institute for Materials Science, Sengen, Tsukuba, Ibaraki, 305-0047, Japan.
bReasearch Institute for Computational Sciences, AIST, Central 2, Tsukuba, Ibaraki 305-8568, Japan.
cDepartment of Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan.
The half-metallic systems will be quite useful in future spin electronics. The LDA in the density functional theory bas been widely used first-principles method, but it is also known that the LDA underestimates band gaps in semiconductors and insulators. The approximation is employed to study La0.7Ba0.3MnO3, which is one of candidates for the half-metallic ferromagnets, to show that the lowest energy of the unoccupied states for the minority spin is far above the Fermi energy compared to that in the LDA. As a bulk, this system is predicted to be a fully-polarized half-metallic ferromagnet.
Orbital Ordering in UGa3: Direct Detection by 69Ga NMR
Shinsaku KAMBEa, Harukazu KATOa, Hironori SAKAIa, Russell E. WALSTEDTa, Dai AOKIb, Yoshinori HAGAa, Yoshichika Ônukib
aASRC, Japan Atomic Energy Research Institute Tokai, Ibaraki 319-1195, JAPAN
bGraduate School of Science, Osaka University Toyonaka , Osaka 560-0043, JAPAN
69Ga NMR spectra are reported and analyzed for the paramagnetic and antiferromagnetically (AFM) ordered states of UGa3(TN=67K). Ordered-state splitting of the NMR lines indicates that the fourfold symmetry of the Ga-site hyperfine (HF) coupling is broken in the AFM state. A striking change in the Ga HF coupling constant also occurs at TN. These effects are attributed to uranium (5f) orbital ordering, which appears to set in just below TN. Orientation of the U moments has been determined as [11d] (0 < d < 1) for 40K < T < TN and [a, b, g] (a,b,g ¹ ) for T < 40K. Electric field gradients and field-dependent HF effects are also discussed.
Specific Heat in Normal Conducting UPt3 Revisited
Stephan Schöttla, Michael Meißnerb, Detlef Güntherb
aNational Physical Laboratory CBTLM, Queens Road, Teddington, Middlesex TW11 0LW, United Kingdom
bHahn-Meitner-Institut BENSC, Glienicker Str. 100, 14109 Berlin, Germany
Using a high-quality single crystal with exceptional superconducting transition temperature we have measured specific heat of UPt3 in the temperature range from 0.3 K to 16 K and in magnetic fields up to 8 T. The focus of this work lies on the normal state properties, where apart from the heavy Fermion behaviour, in neutron scattering experiments magnetic correlations have been found setting in at 6 K. However, this ordering has so far have not been confirmed in thermodynamic measurements. For the first time we observe a peak at 6.7 K that shifts to 3.2 K in 3 T, independent of field direction. We discuss its origin and possible explanations either in terms of the magnetic correlations or impurity contributions.
New Energy Scale in Low Temperature of YbAl3
Takao Ebiharaa, Andrew L. Corneliusb, Jon M. lawrencec
aDepartment of Physics, Shizuoka University, 836 Oya Shizuoka, 422-8529, Japan
bDepartment of Physics, University of Nevada, Las Vegas, Nevada 89154, USA
cDepartment of Physics and Astronomy, University of California, Irvine, California 92697, USA
A new anomaly, which is seen in the specific heat and magnetic susceptibility measurements, is observed at lower temperature than Kondo peak temperature at 150 K in YbAl3. The new peak could associate with a new temperature scale for the development of Fermi liquid coherence in YbAl3. The susceptibility anomaly was suppressed by application of high magnetic fields abve 40T. The magnetization measurement suggests that the low temperature coherent peak disappears when the magnetic field reaches over 40 T. This behavior implies that new character of electronic states in YbAl3 may appear in high magnetic field.
1 N.E.Sluchanko et al., Phys.Rev. B61, 9906 (2000); Physica B 312-313C 331 (2002).
2T.Suzuki et al., Phys. Rev. B 62, 49 (2000).
3O. Yanagisawa et al.: J. Superconductivity, 12, 311 (1999).
4T. Kimura et al., PRB 58, 11081 (1998).
5D. N. Argyriou et al., PRB 61, 15269 (2000).
6A. Imaduddin et al., Physca B, in press.