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Xue–qing Zhao, Jing–fa Lu
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 7 Pages
2151-2152
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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The integrability and hidden symmetry of a coupled dispersionlessequations are analysed by a prolongation approach. A more general formsof the Lax pair of system and its concrete Lie algebraic structures arederived theoretically.
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Shuji Ogata
Subject area: Electronic structure of atoms and molecules: theory.
1999 Volume 68 Issue 7 Pages
2153-2156
Published: July 01, 1999
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Path-integral Monte Carlo simulations for Cs atoms immersed in liquid
4He are performed to investigate the effects of He-exchange on the D
2-excitation energy which shifts or splits depending on the pressure (P) and temperature (T). We find substantial difference in P-dependences of the shift between the cases with T below and above the λ -transition temperature, while weak P-dependences are seen for splitting irrespective of T. Microscopic structures of the liquid around the Cs are investigated through analyses of the He-exchange and the density inhomogeneity.
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Mieko Toida, Daiju Dogen, Yukiharu Ohsawa
Subject area: The physics of plasmas and electric discharges.
1999 Volume 68 Issue 7 Pages
2157-2160
Published: July 01, 1999
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Low-frequency mangnetosonic pulses in a two-ion-species plasma are studiedtheoretically and by simulation with a one-dimensional electromagneticsimulation code based on a three-fluid model, with particular attention to the dynamics of minority heavy ions.It is found that heavy ions can gain some energy from the pulses. Because of this energy transfer, the pulses are damped even if theplasma is collisionless and pulse propagation is perpendicular to themagnetic field.
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Sadao Masamune, Motomi Iida, Hiroshi Oshiyama
Subject area: The physics of plasmas and electric discharges.
1999 Volume 68 Issue 7 Pages
2161-2163
Published: July 01, 1999
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The stability of resistive shell modes (external kink modes) has been analyzed in the RFP configuration surrounded by an external helical current.The helical current is shown to have a stabilizing effect on the external kink modes when the current is in phase with the tangentialcomponent of the magnetic perturbation.The current density required to stabilize the unstable modes increases with the gowth rate of the mode.An increase in the distance of the current layer from the plasma surface alsoleads to an increase in the required current.Therelevance of this stabilizing effect of the helical current tothe experimental observations is discussed.
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Kazuki Koshino, Tetsuo Ogawa
Subject area: Lattice dynamics and crystal statistics.
1999 Volume 68 Issue 7 Pages
2164-2167
Published: July 01, 1999
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We explain theoreticallythe peculiarities of photoinduced low-spin (LS)→high-spin (HS) transitions in spin-crossover complexes, such as the threshold behavior in the excitation light intensity for phase conversionand the existence of the incubation period.Our investigation is based on a modelwhere a single complex is described by the two electronic states and the breathing oscillation mode with the long-range interaction among the complexes.As the spin transition processes, we take into accountthe LS→HS photoexcitation processand the HS→LS nonradiative decay process.The rate for the latter process is sensitive to the LS fraction in the crystalbecause the potential barrier for the HS→LS decayis dependent on the LS fraction through the long-range interaction amongthe complexes;the lifetime of the metastable HS state becomes longeras the LS fraction decreases.Such sensitivity leads to the nonlinear temporal evolution for the LSfraction, which coincides with the experimental results.
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Kazushige Machida, Masanori Ichioka
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 7 Pages
2168-2171
Published: July 01, 1999
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We show that lightly doped La
2-xSr
xCuO
4 can be described in terms of a stripe magneticstructure or soliton picture. The internal relationship between the recent neutronobservation of the diagonal (x=0.05) to vertical (x≥ 0.06) stripe transition, which was predicted, and the concomitant metal-insulator transition, is clarified by soliton physics.The phase diagram with the unidentified transition lines between the antiferromagnetic and stripe phases, the doping dependence of the modulationperiod, and the origin of the mid-infrared optical absorption are investigatedand compared with other single-layer systems, La
2-xSr
xNiO
4and (La, , Nd)
2-xSr
xCuO
4.A novel type of quasi-particles and holes is fully responsible formetallic conductionand ultimately superconductivity.
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Setsuo Misawa
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 7 Pages
2172-2173
Published: July 01, 1999
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The spin susceptibility of a two-dimensional (2D) Fermi liquid hasbeenrecently shown, by Hirashima and Takahashi[J. Phys. Soc. Jpn. 67 (1998) 3816], to vary asχ(T)=χ
0+α T as a function of temperature T, where χ
0andα are constants.From the analytic form of the free energy which is compatible with thisχand the third law of thermodynamics, we can deduce that the entropy S, andhence the heat capacity, of the system varies as T
2.This T
2-term of S is also compatible with the theoretical predictionfor the self-energy part of the 2D quasiparticles.
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Dai S. Hirashima, Katsunori Kubo
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 7 Pages
2174-2177
Published: July 01, 1999
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The nonanalytic contribution to the free energy of interacting two-dimensional fermion systems is studied numerically. It is found that the numerical result for the singular contribution is well fitted bya form of B
TT
2√{T
2+(b
HH)
2}+B
HH
2√{(b
TT)
2+H
2} where T is the temperature, H the magnetic field and b
T, b
H, B
T and B
H are constants.Consequences of this singularity are discussed. The effects of impurityscattering are also briefly discussed.
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Hiroki Nakano, Yukitoshi Motome, Masatoshi Imada
Subject area: Electronic transport in condensed matter.
1999 Volume 68 Issue 7 Pages
2178-2181
Published: July 01, 1999
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Taking the orbital degeneracy of e
g conduction bands and the Coulomb interaction into account in a double-exchange model, we investigate the charge dynamics of perovskite Mn oxides by the Lancz&ddotos; diagonalization method. In the metallic phase near the Mott insulator, it is found that the optical conductivity for a spin-polarized two-dimensional system exhibits a weight transfer to a broad and incoherent structure within the lower-Hubbard band together with a suppressed Drude weight. It reproduces a qualitative feature of the experimental results. As an orbital effect, we find that an anomalous charge correlation at quarter filling suppresses the coherent charge dynamics and signals precursor to the charge ordering.
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Dai Aoki, Piotr Wisniewski, Kohsaku Miyake, Narumi Watanabe, Yoshihiko ...
Subject area: Electronic transport in condensed matter.
1999 Volume 68 Issue 7 Pages
2182-2185
Published: July 01, 1999
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We have grown high-quality single crystals of tetragonal USb
2 using a flux method.We have detected five branches in de Haas-van Alphen (dHvA) experiments.Frequencies of all dHvA branches follow the 1/cosθ-dependence, revealing the presence of cylindrical Fermi surfaces, where θ is a tilt angle from [001] to [100].The cyclotron masses are in the range from 1.84 to 8.33, m
0.The two-dimensional Fermi surfaces are due to the conduction electrons in the U-plane, including the itinerant 5f /-electrons.
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Minoru Kawamura, Akira Endo, Shingo Katsumoto, Yasuhiro Iye
Subject area: Electronic transport in condensed matter.
1999 Volume 68 Issue 7 Pages
2186-2189
Published: July 01, 1999
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Vertical transport in GaAs/AlGaAs superlatticeshas been studied in the quantum Hall regime.Both the in-plane and out-of-plane resistances exhibit an Arrhenius-type temperature dependencewith small values of activation energy.At very low temperatures, the out-of-plane conductancebecomes almost temperature independentand its values scale with the sample perimeter, indicating that the current is carriedby the chiral surface states.The vertical transport in this regime exhibitsdistinct non-Ohmicity, suggestingthe onset of bulk transport at high bias voltages.Rather strong non-Ohmicity is also observedin the low bias voltage region where the chiral surface state is responsiblefor the vertical transport.
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Masaki Takata, Eiji Nishibori, Kenichi Kato, Makoto Sakata, Yutaka Mor ...
Subject area: Electronic structure and electrical properties of surfaces, interfaces and thin films.
1999 Volume 68 Issue 7 Pages
2190-2193
Published: July 01, 1999
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We have investigated the charge-density distribution of an antiferromagnetic bi-layered manganite, NdSr
2Mn
2O
7, by the maximum entropy method (MEM) using the synchrotron X-ray powder data. The magnetic structure below T
N=150, K is known to be a layered-type (A-type). We have found a significant change of the electron distribution around the Mn site below T
N. Our observation indicates dx
2-y
2-orbital polarization in the A-type antiferromagnetic state.
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Masaki Shigemori, Akira Shimizu, Tobias Brandes, Jun–ichi Inoue
Subject area: Superconductivity.
1999 Volume 68 Issue 7 Pages
2194-2197
Published: July 01, 1999
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We study high-density electron-hole (e-h) systems with the electron density slightly higher than the hole density. We find a new superconducting phase, in which the excess electrons form Cooper pairs moving in an e-h BCS phase. The coexistence of the e-h and e-e orders is possible because e and h have opposite charges, whereas analogous phases are impossible in the case of two fermion species that have the same charge or are neutral. Most strikingly, the e-h order enhances the superconducting e-e order parameter by more than one order of magnitude as compared with that given by the BCS formula, for the same value of the effective e-e attractive potential λ
ee. This new phase should be observable in an e-h system created by photoexcitation in doped semiconductors at low temperatures.
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Takanobu Jujo, Kosaku Yamada
Subject area: Superconductivity.
1999 Volume 68 Issue 7 Pages
2198-2201
Published: July 01, 1999
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The explanation of the anomalous behavior in κ-type (BEDT-TTF)
2Xwhich was revealed by the nuclear magnetic resonance experiments is presented. We calculate the electronic properties by using the one-loop approximation for the superconducting fluctuation. The decrease of the density of states due to the large damping effect is obtained and the one-particle spectrum has a pseudogap structure around the Fermi level. It is found that these behaviors are peculiar to the quasi two-dimensional system and are enhanced in the incoherent metal. The similarity between the cuprates and this compounds is discussed and an experiment to check this proposal is suggested.
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Masato Kubota, Hideki Yoshizawa, Yutaka Moritomo, Hirofumi Fujioka, Ka ...
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2202-2205
Published: July 01, 1999
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We demonstrate that the 50&LaSr;
2Mn
2O
7 exhibits CE-type charge- and spin-ordered statesbelow T
N, COA=210, K and below T
NCE --145, K, respectively. However, the volume fraction of the CE-type ordering isrelatively small, and the system is dominated by the A-type spin ordering. The coexistence of the two types of ordering is essential to understand the transport properties, and it can be viewed as an effective phase separationbetween the metallic d(x
2-y
2) orbital ordering and thecharge-localized d(3x
2-r
2)/d(3y
2-r
2) orbital ordering.
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Takashi Nagata, Hirokazu Fujino, Jun Akimitsu, Masakazu Nishi, Kazuhis ...
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2206-2209
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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We report on specific heat and neutron scattering measurements performed for Sr
14-xCa
xCu
24O
41 single crystals. The specific heat data of Sr
2.5Ca
11.5Cu
24O
41 showed a sharp phase transition at T
N≈2.1, K, indicating the possible onset of a long-range order. Specific heat measurements under magnetic fields also revealed that this phase transition is not due to charge ordering or structural phase transition but to magnetic ordering. In the neutron scattering experiments, we observed several Bragg peaks, corresponding to the magnetic ordering observed in the specific heat measurements. Furthermore, we confirmed from polarized neutron scattering measurements that these Bragg peaks are undoubtedly magnetic in origin. Considering both the nuclear magnetic resonance and neutron scattering data, a possible magnetic structure on the chain and ladder sites has been proposed. In this system, the singlet state and antiferromagnetic order induced by appropriate hole-doping coexist at ambient pressure and the dissolved hole pairs move under high pressure, leading to the occurrence of superconductivity.
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Mitsuru Toda, Takao Goto, Meiro Chiba, Kimio Adachi, Naoshi Suzuki
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2210-2213
Published: July 01, 1999
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The temperature dependence of the spin-lattice relaxation time T
1 of
133Cs in CsFeCl
3 was measured from 1.5 to 20, K with external fields up to 7, T applied along the c-axis, and the analysis was performed on the basis of the dynamical correlated-effective-field approximation theory. T
1-1 below 2, T, which decreases markedly with decreasing temperature, was well interpreted in terms of the longitudinal spin fluctuation characterized by a large energy gap. For higher fields however, T
1-1 exhibited an almost temperature-independent behavior accompanied by an significant increase below 5, K. The latter feature was ascribed to the transverse spin fluctuation associated with the softening of the lower branch of the excited doublet around the K-point.
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Masayuki Hagiwara, Yasuo Narumi, Kazuhiko Minami, Keiji Tatani, Koichi ...
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2214-2217
Published: July 01, 1999
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We report the results of magnetization measurements on powder samples of [NiCu(pba)(D
2O)
3]·2D
2O (pba=1, 3-propylenebis(oxamato), C
7H
6N
2O
6) and [Ni(dpt)(H
2O)Cu(pba)]·2H
2O (dpt=bis-(3-aminopropyl)amine, C
6H
17N
3), which are regarded as the S=1/2 and 1 ferrimagnetic chain and dimer, respectively. The magnetization curve in pulsed magnetic fields up to about 50, T of each compound shows an increase with increasing field at low magnetic fields and reaches a plateau of about 1.1, μ
B/(formula unit) which corresponds to about one-third of the saturation magnetization. Magnetization of the former compound in static magnetic fields up to 7, T is compared with that of the latter one in addition to the comparison of results of some numerical calculations. We have found that the ferrimagnetic chain has a ferromagnetic feature at low magnetic fields in contrast to the ferrimagnetic dimer and that the calculated magnetization increases with increasing number of composed spins.
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Hiroshi Furuta, Tokiyoshi Matsuda, Chihiro Yamanaka, Motoji Ikeya
Subject area: Materials science.
1999 Volume 68 Issue 7 Pages
2218-2220
Published: July 01, 1999
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A spatial structure of porous silicon formed by anodization was simulated using a lattice model considering the quantum confinement effect. Calculation starting from a random distribution of null cells at the surface yielded the final granular, columnar or flat surface structures depending on the magnitude of the anodizing bias voltage in concordance with previously reported structures. Our calculations suggest that columnar and dendritic structures can be produced in degenerately doped p-type Si wafers by self-organization of nanowires with quantum confinement effects.
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Masato Hisakado
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 7 Pages
2221-2227
Published: July 01, 1999
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We consider the hungry Volterra hierarchy from the view point of the multi boson KP hierarchy.We construct the hungry Volterra equation as the Bäcklund transformations (BT) which are not the ordinary ones.We call them “fractional” BT.We also study the relations between the (discrete time) hungry Volterra equation and two matrix models.From this point of view we study the reduction from (discrete time) 2d Toda lattice to the (discrete time) hungry Volterra equation.
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Yasuhiro Fujii, Miki Wadati
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 7 Pages
2228-2233
Published: July 01, 1999
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The asymmetric XXZ chain is studied in the framework of the algebraic Bethe ansatz. The model is one of the Heisenberg XXZ spin chains with Dzyaloshinsky--Moriya interactions and is mapped onto the asymmetric six-vertex model. We calculate the scalar products that constitute various correlation functions of the model, by the Korepin's method. They are expressed in terms of determinants of the dual quantum fields.
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Kazuhiro Hikami, Rei Inoue, Yasushi Komori
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 7 Pages
2234-2240
Published: July 01, 1999
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We introduce a vertex model in two-dimension, which is associated withthe Bogoyavlensky lattice.We show that in a crystallized limit (q→ 0)we have a unique configuration, and that it coincides with anevolution of the soliton cellular automata which is a generalizationof the system introduced by Takahashi and Satsuma.
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Takayuki Tsuchida, Miki Wadati
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 7 Pages
2241-2245
Published: July 01, 1999
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Higher flows of the Heisenberg ferromagnet equation and the Wadati-Konno-Ichikawa equationare generalized into multi-component systems on the basis of the Lax formulation. It is shown that there is a correspondence between the multi-component systems through a gauge transformation. An integrable semi-discretization of the multi-component higher Heisenberg ferromagnet system is obtained.
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Ryuusuke Takashima, Masayoshi Tajiri
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 7 Pages
2246-2251
Published: July 01, 1999
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A lattice soliton solution with doubly periodic structure in the x-y plane is constructedas the imbricate series of rational soliton solutions to the Davey-Stewartson equation, which seems doubly periodic arrays of the infinite rational solitons. The existence condition and some properties of the lattice soliton solution are also presented.
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Alexander N. Drozdov, Shigeo Hayashi
Subject area: Statistical physics and thermodynamics.
1999 Volume 68 Issue 7 Pages
2252-2258
Published: July 01, 1999
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The thermally activated escape of a Brownian particle over anenergy barrier of arbitrary shape is considered. Based on theexpansion of the underlying Fokker-Planck equation in reciprocalpowers of the friction constant a rate expression is constructed. Itagrees in the limiting case of high friction with the rate followingfrom the corresponding Smoluchowski equation and, in the limit of weakfriction with the rate obtained from transition state theory. Itsaccuracy is tested for Brownian motion over a parabolic barrier inwhich case we compare to the known analytic Kramers result.Applications to cusp shaped and quartic barriers show that theapproximate rate expression is in very good agreement with accurateestimates of the rates from numerical simulations. An overall rateexpression valid in the whole friction range is then obtained by usingthe Mel'nikov-Meshkov result for the underdamped Brownian motion, alongwith a properly defined energy loss of the particle per oscillation.Its validity is tested by comparing with exact numerical rates ina cusped double well potential.
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Shang H. Kim
Subject area: Electricity and magnetism: fields and charged particles.
1999 Volume 68 Issue 7 Pages
2259-2268
Published: July 01, 1999
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It is found that the net work per unit time done by all electrons in the cavity is far smaller than the measured power of induced emission in the first free-electron laser (FEL). The measured powers of spontaneous and induced emissions in the first FEL are identified as those of spontaneous and net stimulated transverse-wiggling-driven free-electron two-quantum Stark (TWFETQS) emissions, respectively, which are conceivable only in quantum wiggler electrodynamics (QWD). The uncertainty principle prescribes that an electron plasma with density n cannot exhibit net stimulated emission of wavelength λ, and the reaction force arisen from laser radiation of wavelength λ is independent of the electron phase with respect to the laser radiation if nλ
3>> 1. It is found from these facts, the concept of Liénard-Wichert potentials, and the momentum and energy conservations that in the Raman FEL lasing must be an amplified spontaneous TWFETQS emission, and the net work due to phase bunching by the laser field and the magnetic wiggler is equal to the radiated energy. To confirm the validity of the QWD law that the wave-function phase of a final state arrived through an interaction with a wiggler is random, forward Raman scattering (FRS) in an experiment is quantum-mechanically calculated without presumption on the wave-function phase. It is found that the occurrence of the FRS in measurable magnitude is not feasible unless the QWD law is valid. Since the FRS is exhibited in the experiment, we conclude that the QWD law is valid.
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Abdel–Shafy F. Obada, Ahmad M. Abdel–Hafez, Mahmoud Abdel& ...
Subject area: Optics.
1999 Volume 68 Issue 7 Pages
2269-2275
Published: July 01, 1999
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The influence of Stark shift on the phase properties when an ideal cavity is filled with a Kerr-like medium and coupling is effected through nondegenerate Raman two-photon processes is studied. This has been carried out using the Hermitian phase formalism of Pegg and Barnett. We find that the phase properties of the field reflect the collapses and revivals of the level occupation probabilities in most situations. The interaction brings about the symmetrical splitting of the phase probability distribution. A number of interesting features are found and discussed.
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Ali Maghari, Hassan Behnejad, Farzin Nematbakhsh
Subject area: Kinetic and transport theory of fluids; physical properties of gases.
1999 Volume 68 Issue 7 Pages
2276-2280
Published: July 01, 1999
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A correlation equation for the low-density viscosity collision integral of hydrogen molecules over a very large temperature range is obtained. This equation has been inverted directly to give the reduced intermolecular potential energy curve for H
2--H
2 corresponding to the collision integral. The results are then used to obtain a best Morse-Spline-Van der Waals (MSV) potential model. Comparison is made between the present interaction potential energy function and two other previously published H
2--H
2 potential energy functions. The present potential function provides the best overall agreement for the available low-density gas phase thermophysical data, i.e. second virial coefficient and transport properties, and can thus be recommended for calculation of all properties that depend upon the intermolecular interaction.
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Mitsuaki Nagata
Subject area: The physics of plasmas and electric discharges.
1999 Volume 68 Issue 7 Pages
2281-2286
Published: July 01, 1999
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From the previously reported equation for the drift velocity of electrons with relativistic energies, two interesting results (the negative magneto-resistance and the negative resonance absorption) were discovered. One problem is that, in derivation of the new drift velocity equation, the delta-function distribution was used for the velocity distribution of electrons immediately after the scattering. So the dependences of these two effects upon the shape of the velocity distribution are investigated. Also, since the new equation is different from the classical drift velocity equation, the physical meaning of the difference is discussed in Appendix.
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Takahiro Onimaru, Hideya Onodera, Kenji Ohoyama, Hiroki Yamauchi, Yasu ...
Subject area: Structure of liquids and solids; crystallography.
1999 Volume 68 Issue 7 Pages
2287-2291
Published: July 01, 1999
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Crystal structures of CeB
2C
2 and NdB
2C
2 were investigated by means of neutron powder diffraction using
11B enriched samples. Diffraction patterns of Ce
11B
2C
2 and Nd
11B
2C
2 are very similar to each other, and Rietveld analyses reveal that the crystal structure belongs to a symmetry group of tetragonal P4/mbm, where the rare earth atoms occupy 2(a) sites and the B and C atoms occupy two 4(h) sites with different positional parameters. The newly determined structure differs from previously reported ones with P4/mbm and P{&overline; 4}2c mainly in the site positions occupied by the B and C atoms. The B and C atoms form network planes consisting of non-regular squares and octagons.
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Mitsuaki Ginoza, Makoto Yasutomi
Subject area: Structure of liquids and solids; crystallography.
1999 Volume 68 Issue 7 Pages
2292-2297
Published: July 01, 1999
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An analytical function is presented of the measurable structure factor of a multi-species polydisperse Percus-Yevick fluid consisting of spherical particles with Schulz distributed diameters. As a demonstration, polydispersity effects on some structural properties in the single species polydisperse fluid are investigated. These properties include the measurable structure factor, the structure factor describing the total density fluctuation, and the differential cross section of the particle scattering. A discussion is also given on their behaviours by comparing them with each other.
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Dmitri V. Louzguine, Masatoshi Saito, Yoshio Waseda, Akihisa Inoue
Subject area: Structure of liquids and solids; crystallography.
1999 Volume 68 Issue 7 Pages
2298-2303
Published: July 01, 1999
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The structure of an amorphous Ge
50Al
40Cr
10 alloy was studied by conventional X-ray diffraction, anomalous X-ray scattering and transmission electron microscopy including high-resolution imaging. The anomalous X-ray scattering profiles were obtained at Ge and Cr K-absorption edges. Structural information in the form of interference function obtained by the experimental methods was checked for its correctness by using the reverse Monte Carlo simulation method. The structure of the alloy studied is discussed on the basis of transmission electron microscopy images, an ordinary radial distribution function, partial structure functions and partial pair distribution functions.
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Crystallographic Parameters of Atoms in the Single Crystals of the Compounds RB6 (R=Y, , La, , Ce, , Nd, , Sm, , Eu, , Gd)
Yasuhiko Takahashi, Ken–ichi Ohshima, Fujio P. Okamura, Shigeki ...
Subject area: Structure of liquids and solids; crystallography.
1999 Volume 68 Issue 7 Pages
2304-2309
Published: July 01, 1999
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The lattice parameters, bond length between rare-earth metals R and boron atoms, intra- and inter-bond lengths between boron atoms and temperature parameters of constituent atoms in rare-earth hexaborides RB
6 (R=Y, , La, , Ce, , Nd, , Sm, , Eu, , Gd) were determined by analyzing integrated X-ray intensities with the use of ultra-short wavelength at room temperature. These parameters were related to the peculiar physical properties in the compounds. The Einstein temperature of rare-earth metals in the crystal structure of RB
6 (R=La, , Ce, , Nd, , Sm, , Eu, , Gd) has also been determined by analyzing the temperature dependence of integrated X-ray intensities. Except for EuB
6, the value is monotonously decreasing with increasing atomic number.
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Takao Ohta
Subject area: Equations of state, phase equilibria, and phase transitions.
1999 Volume 68 Issue 7 Pages
2310-2316
Published: July 01, 1999
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We formulate a theory of martensite aging in shape memory alloys.A time--dependent Ginzburg--Landau type equation is introducedfor the local strain which is the order parameter of the martensitic phase.It is assumed that the order parameter is coupled with a secondary variable whose time evolution is extremely slow. Fromthis set of equations, we derive the equation of motion for a twin boundary. The stress--strain relation due to the motion of twin boundaries is obtainedby taking account of the aging effect associated with the slow evolution ofthe secondary variable. The results are found to be consistentwith the rubber--like behavior observed experimentally. Stabilization of the martensitic phase by aging isalso explained.
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Katsunori Kubo, Dai S. Hirashima
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 7 Pages
2317-2325
Published: July 01, 1999
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Effects of the Hund's rule coupling in an orbitally degenerate Andersonmodel are studied by a quantum Monte Carlo method. From results for static as well as dynamic susceptibilitiesit is concluded that the system remains a local Fermi liquidat least in a weak to intermediate coupling region as was concluded inprevious studies. It is also foundthat the Hund's rule coupling generates a strong attractive interaction between conduction electrons with parallel spins in the same orbitalstates.
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Takehide Koyama, Hiroshi Sugita, Shinji Wada, Kitomi Tsutsumi
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 7 Pages
2326-2330
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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The
45Sc,
59Co and
29Si nuclear magnetic resonances in the ternary compound Sc
5Co
4Si
10 have been studied. Quadrupole splitted powder-patterns were observed with ν
Q=e
2qQ/14{(h/2π)}=0.41 MHz and η ~= 0 for
45Sc, and ν
Q=1.68 MHz and η=0.44 for
59Co, respectively. The temperature independent Knight shifts and the Korringa-like behaviors of the relaxation rate indicate that the system belongs to Pauli paramagnetic metals: K(
45Sc) -- 0∧ K(
59Co)=0.65&The; analysis of the Knight shifts and the relaxation rates leads to a conclusion that the density of states at the Fermi level is dominated by the Co d bands of pentagon-hexagon layers, while the d bands of Sc layers which separate the pentagon-hexagon layers are near empty.
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Tatsuya Fujii, Norio Kawakami
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 7 Pages
2331-2337
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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Critical properties in the dynamical charge correlation function for the one-dimensional Mott insulatorare studied. By properly taking account of the final-state interaction between the charge and spin degrees of freedom, we find that the edge singularity in the charge correlation function is governed by massless spinon excitations, although it is naively expected that the spinons do not directly contribute to the charge excitationover the Hubbard gap. We obtain the momentum-dependent anomalous critical exponent by applying the finite-size scaling analysis to the Bethe ansatz solution of the half-filled Hubbard model.
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Satoru Ohno, Masaki Togashi, Adrian C. Barnes, John E. Enderby
Subject area: Electronic transport in condensed matter.
1999 Volume 68 Issue 7 Pages
2338-2343
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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The electrical conductivity, σ, and thermoelectric power, S, of molten (AgCl)
1-c(Ag
2Te)
c have been measured as a function of temperature. The conductivity decreases rapidly on the addition of AgCl to liquid Ag
2Te and it reaches a minimum at c=0.2. The positive value of S on the Ag
2Te-rich side decreases gradually as the concentration of AgCl is increased. The large value of S on the AgCl-rich side decreases rapidly on addition of Ag
2Te. As a result, the composition dependence of S shows a minimum with a negative value near c=0.5. The competition of the electronic and ionic transport in these mixtures is reflected in the temperature dependence of thermoelectric power for the mixtures with 0.3 ≤ c ≤ 0.5. The electrical behaviour of molten mixtures with c ≥ 0.6 was analysed by using the electronic model of liquid semiconductors.
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Mitake Miyazaki, Keita Kishigi, Yasumasa Hasegawa
Subject area: Superconductivity.
1999 Volume 68 Issue 7 Pages
2344-2350
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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We have investigated the transition temperature T
c(H) of superconductivity in quasi-two-dimensional (Q2D) tight-binding electrons in a strong magnetic field. When the magnetic field is parallel to 2D conducting plane, T
c(H) of the Q2D superconductor is shown to increase in an oscillatory manner as the magnetic field becomes large and to reach T
c(0) in a strong magnetic field limit for the spin-triplet superconductor. We consider the cases of on-site and nearest sites attractive interaction, and calculate the magnetic field dependences of the transition temperature for various types of symmetry. The first order transition from p
y-wave to p
x-wave is shown to occur at H-- 100 T when the magnetic field is parallel to the y direction, which will be observed in a triplet superconductor, Sr
2RuO
4.
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Kiyoichiro Motoya, Satoshi Kubota, Keisuke Nakaguchi
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2351-2360
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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A magnetic phase diagram of a Heusler type alloy system Cu
2(Mn
xTi
1-x)Al with x≥ 0.5 has been determined by magnetic susceptibility measurements. Reentrant spin-glass transition exists over a wide concentration range. Quasi-elastic neutron scattering measurements on a single crystal of Cu
2(Mn
0.70Ti
0.30)Al, which transforms paramagnetic→ ferromagnetic→ spin-glass phases, have shown that a large number of magnetic clusters of average size d-- 300, Å exist in the ferromagnetic phase. On cooling down, the number of clusters increases and the average size gradually decreases to d-- 200, Å at T=10, K. Inelastic neutron scattering measurements have shown that highly damped spin-wave excitations exist in the ferromagnetic phase. The amplitude as well as the stiffness constant of the spin-wave decrease as the temperature decreases toward T
S.G., which is consistent with the macroscopic property. The origin of anomalous temperature variation property of spin-wave parameters observed in other reentrant spin-glass systems has been discussed.
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Yu–qiang Ma
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2361-2365
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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We propose a bosonic spherical model to investigate the phase transitionand critical behaviors of the quantum XY ferromagnet. We calculatethe low-temperature thermodynamics and critical exponents near thephase transition, and compare withthe results of the conventional spherical model in the spin space. Thepossibilities of the existence of the ordered phaseof the system are examined for d < 2 and d=3, respectively. The effects of the exchange anisotropy on the phase transition temperature are also discussed.
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Yoshiharu Kanegae, Yoji Ohashi, Hiroaki Ikeda
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2366-2372
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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Nuclear magnetic ordering is investigated in scandium crystal by the Monte Carlo simulation. We determine the phase diagram in the ground state with respect to interactions between the nuclear spins. In this phase diagram, we find a ferrimagnetic state with the total magnetization being smaller than the complete ferromagnetism by 1/3: This state changes into the ferromagnetism at a finite external magnetic field, which leads to a threefold jump in the magnetization as was observed by the experiment. Thus, this state is a strong candidate for the nuclear magnetic ordering in scandium below T<~ 2[μK].
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Akihisa Koga, Seiya Kumada, Norio Kawakami
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2373-2379
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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Quantum phase transitions between the magnetically orderedand disordered states are studied for the two-dimensionalantiferromagnetic quantum spin systems with ladder, plaquette, and mixed-spin structures. Starting with properly chosensinglet-cluster configurations, we perform the series expansionfor the staggered magnetic susceptibility. The phase boundaryis determined by applying the Dlog and biased Padé approximantsto the staggered susceptibility thus obtained. The resulting phasediagram allows us to discuss the quantum phase transitionsquantitatively, which agrees fairly well with the quantum MonteCarlo results for several cases previously studied.
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Jiro Kitagawa, Masayasu Ishikawa
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2380-2383
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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By measuring the magnetic susceptibility, the specific heat and the electrical resistivity, we have investigated the low-temperature properties of new compounds CePd
2Ga
2 and LaPd
2Ga
2 with the tetragonal CaBe
2Ge
2-type structure. The former compound shows antiferromagnetic ordering at 2.3 K and a structural phase transition into a triclinic structure at 125 K, and the latter is superconducting below 1.9 K and shows a similar structural transition at 62 K. From the analysis of published data, it is proposed that the c/a ratio may be a decisive parameter for the structural instability in CaBe
2Ge
2-type compounds.
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Jie Yang, Jue–lian Shen, Hai–qing Lin
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2384-2389
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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The finite temperature properties of the frustrated quantum antiferromagnetic J
1-J
2 model are studied by an extended self-consistent mean-field method. The specific heat and the spin-spin correlations are obtained in both the Néel and collinear state limits. Results of our calculations are compared with that obtained by the exact diagonalization studies on finite lattices and by the variational spin wave approach.
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Ryousuke Shiina, Hiroyuki Shiba, Osamu Sakai
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2390-2394
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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The stability of quadrupolar domains in TmTe is studied theoretically. Starting from the decoupled four sc sublattices in the Tm fcc lattice, we analyze the inter-sublattice coupling originating from the electrostatic interaction of quadrupoles. It is shown that the single-K state is stabilized among possible combinations of multi-K ordering pattern. The stable K-domains in weak magnetic fields are predicted for various field directions.
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Toshifumi Itakura, Yoshikazu Suzumura
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2395-2404
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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Spin density wave (SDW) state of a quasi-one-dimensional organic conductors near the quarter-filling has been examined in the presence of dimerization, which leads to properties of half-filling. By applying a transfer integral method to a single chain with molecular fields determined self-consistently, it has been shown that two kinds of commensurate states appear for a small misfit parameter due to a competition between the commensurability energy and the dimerization energy. Several phase diagrams of the commensurate state and the incommensurate state have been obtained as the function of misfit parameter, temperature and dimerization.
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Yasushi Ishikawa, Hidetoshi Fukuyama
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2405-2413
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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The spatial distribution of electric current under magnetic fieldand the resultant orbital magnetismhave been studied for two-dimensional electrons under a harmonic confining potentialV(r)=m ω
02 r
2/2in various regimes of temperature and magnetic field, andthe microscopic conditions for the validity of Landau diamagnetism areclarified. Under a weak magnetic field (ω
c <~ ω
0, ω
c being a cyclotron frequency)and at low temperature (k
B T <~ (h/2π)ω
0), where the orbital magnetic moment fluctuates as a function ofthe field, the currents are irregularly distributed paramagnetically or diamagnetically inside the bulk region.As the temperature is raised under such a weak field, however, the currents in the bulk region areimmediately reduced and finally there only remains the diamagnetic current flowing along the edge. At the same time, the usual Landau diamagnetism results for the totalmagnetic moment.The origin of this dramatic temperature dependence is seen to be in the multiple reflection of electron waves by the boundary confining potential, which becomes important oncethe coherence length of electrons gets longerthan the system length.Under a stronger field (ω
c >~ ω
0), on the other hand, the currents in the bulk region cause de Haas-van Alphen effect at low temperature as k
B T <~ (h/2π)ω
c.As the temperature gets higher (k
B T >~ (h/2π)ω
c) under such a strong field, the bulk currents are reduced and the Landau diamagnetism by the edge currentis recovered.
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Genta Masada, Keisuke Tajima
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2414-2419
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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The crystal lattice modulation of Er which is induced by various magnetic structures has been studied by means of X-ray diffraction technique under magnetic field along the a-axis of the hexagonal close packing crystal structure. At 35, K, the 2nd and 4th order satellites caused by the lattice modulation have been observed below the magnetic field of 4.5, T, but the 6th order satellite appeared above 4.5, T in addition to the 2nd and 4th order satellites. The result indicates the fan magnetic structure appeared above 4.5, T is strongly distorted. The magnetic phase diagram obtained by the present experiment is compared with the results by neutron diffraction.
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Kazuyuki Matsuhira, Toshiro Sakakibara, Kunihiko Maezawa, Yoshichika O ...
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 7 Pages
2420-2425
Published: July 01, 1999
Released on J-STAGE: October 01, 1999
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Volume effect in the temperature and field variation of the specific heat C(T, H) of CeRu
2Si
2 was examined by means of detailed thermal expansion measurement performed at temperatures T ≥q 1.5 K in magnetic fields H ≤ 78 kOe. Making use of thermodynamic relations and the scaling properties that hold in the system, the specific heat C
V at constant volume is estimated from experimental values of C
P at constant pressure. We show that the double-peak structure in C
P/T vs. H curve, recently observed by Aoki et al. across the metamagnetic critical region, still remains in the constant volume condition; it is likely to be intrinsic in origin. We have also examined the thermal expansion of the diluted system Ce
0.85(La
0.63Y
0.37)
0.15Ru
2Si
2 where metamagnetism is absent. Remarkable difference in the field variation of the thermal expansion coefficient between these two systems below 10 K demonstrates the existence of a low energy scale that arises from certain inter-site effect and is relevant for the occurrence of metamagnetism.
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