-
Seiji Miyashita
Subject area: Statistical physics and thermodynamics.
1994 Volume 63 Issue 7 Pages
2449-2452
Published: July 01, 1994
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An idea to overcome the negative sign problem in the quantum Monte Carlo method, using the world line update is proposed and demonstrated in an antiferromagnetic Heisenberg model (s=1/2) on the Δ chain.
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Il–Tong Cheon, Guido Langouche, Karen Milant
Subject area: Nuclear structure.
1994 Volume 63 Issue 7 Pages
2453-2457
Published: July 01, 1994
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We report the first reliable observation of the tiny shifts of energy levels of a nucleus placed between two parallel metallic plates. We observed the absorption of the 81, keV gamma ray from
133Cs induced by the β -decay of
133Ba in a
*BaTiO
3 compound. This Mössbauer experiment was carried out at 4.2, K with the absorber placed between two silicon plates with gold coating. The observed shifts are around 0.95, neV (equivalent to 0.007, mm/s) for the distance of about 2, mm between the two plates.
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Fuyuki Shimojo
Subject area: Electronic structure of atoms and molecules: theory.
1994 Volume 63 Issue 7 Pages
2458-2462
Published: July 01, 1994
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The ultrasoft separable pseudopotential proposed by Vanderbilt [Phys. Rev. B 41 (1990) 7892] is extended to include relativistic effects. The relativistic version of the Vanderbilt pseudopotential is well suited for large-scale electronic-structure calculations, using a plane-wave basis set, of systems containing heavy atoms, and has the same degree of transferability as the original Vanderbilt pseudopotential. The pseudopotential proposed in this letter, which is generated from full relativistic atomic calculations, can be used for nonrelativistic calculations. The usefulness of this new pseudopotential is demonstrated by applying it to the atomic calculation of cesium.
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Akihide Takeda
Subject area: Kinetic and transport theory of fluids; physical properties of gases.
1994 Volume 63 Issue 7 Pages
2463-2466
Published: July 01, 1994
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The effects of anisotropy in scatterings in both elastic and inelastic collisions on the electron transport properties in CF
4 gas have been examined using the extended FTI (flight time integral) method over a wide E/N range from 0.1 to 50, Td. Here, E and N are the electric field and the gas density, respectively and 1, Td is 1× 10
-17, Vcm
2. In this analysis, the differential cross section q(ε, , χ )=q
0(ε )(1+a, cos , χ ), where χ is the scattering angle, is used. The effect of forward scattering with a positive value of “a” positively appears as the increase of drift velocity W particularly in the E/N range of highly anisotropic velocity distribution.
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Osamu Kamimura, Masami Terauchi, Michiyoshi Tanaka, Osamu Fujita, Jun ...
Subject area: Structure of liquids and solids; crystallography.
1994 Volume 63 Issue 7 Pages
2467-2471
Published: July 01, 1994
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An electron diffraction study of an inorganic spin-Peierls system CuGeO
3 was performed. Weak superlattice reflections indexed by (h/2)k(l/2)(h, , k, , l: odd) are observed in electron diffraction patterns taken at about 10, K with the [100] electron incidence. The reflections are interpreted as characteristic of a superlattice structure of the space group Bbcm or Bbmm with cell dimensions a'~= 2a, b'~= b and c'~= 2c and with dimerization of Cu atoms along the quasi-one-dimensional [001] or the [010] direction, which is strong evidence of the spin-Peierls transition. Strong diffuse streaks which run along the c
* -direction through the fundamental reflections are observed at the same temperature. The streaks are attributed to low-frequency transverse acoustic waves of the oxygen octahedra and can be precursors to another phase transformation below the spin-Peierls transition.
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Yuka Tabe, Hiroshi Yokoyama
Subject area: Equations of state, phase equilibria, and phase transitions.
1994 Volume 63 Issue 7 Pages
2472-2476
Published: July 01, 1994
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Depolarized Brewster-angle microscopy revealed a novel two-dimensional (2D) mesophase in Langmuir monolayers of 4-octyl-4'-(3-carboxytrimethyleneoxy) azobenzene, characterized by ubiquitous schlieren textures resulting from the long-range order of in-plane molecular orientations. The lack of half-integral strength disclinations and the presence of a regular array of π -walls, across which the in-plane orientation changes by 180 degrees, indicate the vectorial nature of the underlying order parameter. The monolayer can, therefore, be viewed as a single layer of a bulk smectic C phase or as a 2D polar nematic phase, except for the obvious absence of mirror symmetry with respect to the layer plane. In contrast to the experience with bulk liquid crystalline phases, higher-order point disclinations were often found stable in the monolayer.
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Iwao Takei, Tadashi Kobayashi, Shizuo Nakamura, Kazuo Yamana
Subject area: Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties).
1994 Volume 63 Issue 7 Pages
2477-2480
Published: July 01, 1994
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The surface structure of GdP
5O
14 (gadolinium pentaphosphate) with a ferroelastic domain boundary is investigated by AFM (atomic force microscopy) at room temperature in air. The AFM data are obtained for a 1500-nm-square area (400× 400 data points) on the (100) surface of the sample. The domain boundary is observed as a zigzag pattern about 300, nm in width. The contour map of the surface shows a unique surface structure in which hollows are aligned along the domain boundary; the hollows have a width of about 600, nm and a depth of 2, nm. If the surface image indicates a strain originating from the domain boundary structure, the thickness of the ferroelastic domain wall of GdP
5O
14 is estimated to be about 0.6, μ m at room temperature.
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Tadao Kasuya
Subject area: Electron states in condensed matter.
1994 Volume 63 Issue 7 Pages
2481-2484
Published: July 01, 1994
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Unique anomalous heavy fermion behavior in the charge-ordering low-carrier-density system, Yb
4As
3, has been studied together with a similar compound Sm
4Bi
3 as the reference system. A critical analysis shows that, even in the charge-ordering state, the ratio of the trivalent state is less than one per mole, and a small amount of holes remains at the top of the valence band. Moreover, the trivalent state changes to a pseudogap Kondo state, similar to those in Y-doped YbB
12 and SmB
6. A simplified model was proposed, and it was shown that various anomalous properties, such as peak structures in the resistivity and Hall constant as functions of temperature, their uniform changes with pressure, and a large residual resistivity, are explained well by this model to be consistent with the properties in Sm
4Bi
3.
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Yoshimasa Isawa, Tsuyoshi Hatano
Subject area: Electronic transport in condensed matter.
1994 Volume 63 Issue 7 Pages
2485-2489
Published: July 01, 1994
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We derive an expression for the current in a quantum-dot turnstile device in the lowest order of tunnel processes. The electrochemical potential μ in the quantum dot is determined from the current continuity across both barriers. By the use of the adiabatic approximation, the quantized current plateaus in the I-V curve are obtained for the device with symmetric barriers oscillating with a phase difference π . We find that both the height and the position of the steps change as the gate voltage is varied. We also show how the current and the electron number in a quantum dot vary as a function of time.
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Takeshi Inaoka
Subject area: Electronic structure and electrical properties of surfaces, interfaces and thin films.
1994 Volume 63 Issue 7 Pages
2490-2493
Published: July 01, 1994
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The ground-state electronic structure of a small spherical metal shell is investigated on the basis of the model system composed of valence electrons and a spherical jellium shell (JS). The electron density distribution and the effective one-particle potential are calculated by means of the density functional theory involving the local density approximation. We follow the evolution of the electronic structure as we vary the electron number and the inside radius of the JS, conserving the charge neutrality as a whole. The results of our calculation highlight the characteristics of the electronic structure of the small spherical metal shell, which can be understood in terms of the transition from the electronic structure of the metal sphere to that of the electron system sharply localized around a spherical surface.
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Katsurou Hanazawa
Subject area: Superconductivity.
1994 Volume 63 Issue 7 Pages
2494-2498
Published: July 01, 1994
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The question as to whether d-wave superconductivity is compatible with the small but nonvanishing isotope effects observed in high-T
c copper oxides is addressed. On the assumption that a nonphonon mechanism, most likely via antiferromagnetic spin fluctuations, is dominant in both normal and superconducting states, only a few percent contribution to the quasi-particle damping rate from the electron-phonon interaction gives rise to a correct order of the observed isotope effects. The heavier the isotope mass, the lower T
c becomes, since the damping increases via lowering in frequency of the phonon spectrum. The pairing and pair-breaking effects for YBa
2Cu
3O
7 and La
1.85Sr
0.15CuO
4 are examined, and the impurity-concentration dependence of T
c is briefly discussed.
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Shigemasa Matsuo, Hiroshi Shimahara, Katsuhiko Nagai
Subject area: Superconductivity.
1994 Volume 63 Issue 7 Pages
2499-2502
Published: July 01, 1994
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It is shown that when the triplet pairing interaction is finite in the singlet pairing superconductor, the Fulde-Ferrell (FF) state is significantly enhanced by the mixing effect which is inherent to nonuniform superconducting states in a strong magnetic field. The mixed FF state can exist at higher temperatures than the pure singlet FF state. This may explain the behavior of the recently observed high-field phase of the heavy fermion superconductor UPd
2Al
3. The phase diagram of the second-order phase transition is given for a simple model of s-wave-p-wave mixing state.
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Takashi Nishioka, Koichiro Kimura, Masaaki Kontani, Hiroko Aruga Kator ...
Subject area: Magnetic properties and materials.
1994 Volume 63 Issue 7 Pages
2503-2506
Published: July 01, 1994
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We report on the first measurements of the magnetic susceptibility χ , magnetization M, electrical resistivity ρ and specific heat C for U
5Pd
6. A sharp cusp of χ and a kink of ρ at 15, K indicate that U
5Pd
6 orders antiferromagnetically below the Néel temperature T
N=15, K. The specific heat shows a λ -type anomaly at T
N, while the entropy associated with the antiferromagnetic transition is only 0.13R, ln, 2. C/T takes a minimum at -- 3, K, increasing with decreasing temperature and its extrapolation to T→ 0, K gives the electronic specific coefficient of γ -- 220, mJ/K
2, mol-U. γ increases slightly in magnetic fields. It is suggested from these experiments that U
5Pd
6 is a heavy fermion material whose heavy fermion state develops in antiferromagnetic order.
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Tsutomu Momoi
Subject area: Magnetic properties and materials.
1994 Volume 63 Issue 7 Pages
2507-2510
Published: July 01, 1994
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We study the spin-wave spectrum of the Heisenberg antiferromagnet on a bipartite lattice. The spin-wave spectrum on a Néel-ordered ground state is bounded as ε (k)≤ c| k|, where c gives an upper bound for the spin-wave velocity. In the large-S limit, the upper bound c coincides with the result of the spin-wave theory.
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Hidetsugu Kitatani, Takahiro Kakiuchi, Nobuyasu Ito, Masuo Suzuki
Subject area: Magnetic properties and materials.
1994 Volume 63 Issue 7 Pages
2511-2513
Published: July 01, 1994
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Layered square-lattice ferromagnetic Ising models (∞ × ∞ × n lattices) are studied by the Monte Carlo simulation for n=3 to 7. The results show the dimensionality crossover from the two-dimensional square lattice Ising model to the three-dimensional simple cubic Ising model. Furthermore, the CAM analysis is performed to evaluate the critical exponent γ of the three-dimensional simple cubic ferromagnetic Ising model, which shows that γ =1.21(4). The present analysis is also applicable to the study of the phase transition of quantum spin systems.
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Kazuo Hida
Subject area: Magnetic properties and materials.
1994 Volume 63 Issue 7 Pages
2514-2517
Published: July 01, 1994
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The natural explanation of the excitation spectrum of the spin-1 antiferromagnetic Heisenberg chain is given from the viewpoint of the spin-1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain. The energy spectrum of the latter is calculated with fixed momentum k by numerical diagonalization of finite-size systems. It consists of a branch of a propagating triplet pair (triplet wave) and the continuum of multiple triplet waves for weak ferromagnetic coupling. As the ferromagnetic coupling increases, the triplet wave branch is absorbed in the continuum for small k, reproducing the characteristics of the spin-1 antiferromagnetic Heisenberg chain.
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Yutaka Itoh, Hiroshi Yasuoka
Subject area: Magnetics resonances and relaxations in condensed matter; MÖssbauer effect.
1994 Volume 63 Issue 7 Pages
2518-2521
Published: July 01, 1994
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Temperature (T) dependence of the static and the dynamic electron spin-spin correlation is discussed through the planar
63Cu(2) nuclear spin-spin relaxation rate 1/
63T
G and the spin-lattice relaxation rate 1/
63T
1T for YBa
2Cu
3O
6.6 (T
c-- 60, K), YBa
2Cu
4O
8 (T
c-- 82, K), YBa
2Cu
3O
6.98 (T
c-- 92, K), and Tl
2Ba
2CuO
6+δ (T
c-- 85, K). The restricted moment sums S=(
63T
1T)
AF/(
63T
G)
2 [-- χ (Q)Γ(Q)] for the lightly doped Cu oxides tend to have constant values at high temperatures and those for the other ones are nearly T-independent at all the measured T (T
c63T1)AF∝ Tχ (Q) for the antiferromagnetic Fermi liquid model. From the experimental values of S, we estimate the ratio 2α sTA/T0 of the characteristic spin-fluctuation parameters 2α sTA and T0.
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Jean Guy Caputo, Nikos Flytzanis, C. N. Ragiadakos
Subject area: Mathematical methods in physics.
1994 Volume 63 Issue 7 Pages
2523-2531
Published: July 01, 1994
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We examine the singularities in the collective coordinate equations obtained by a variational method for the description of localised solutions of Klein-Gordon models. Following a procedure from Riemannian geometry we show that the scalar curvature for the tensor associated to the kinetic energy remains finite at the singularity; this indicates that the above singularity is not essential and can be removed by a proper choice of coordinates. For the sine-Gordon breather and the kink antikink solutions in φ
4 we present transformations which remove the singularity without changing the ansatz.
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M. Mattes, M. Sorg
Subject area: Classical and quantum physics: mechanics and fields.
1994 Volume 63 Issue 7 Pages
2532-2537
Published: July 01, 1994
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The theory of Relativistic Schrödinger Equations offers a local-realistic interpretation for the Bohm-Aharonov effect. The wave function ψ (x) is built up by a (scalar) localization field l(x) and a kinetic (vector) field k
μ (x), which extends far beyond the support of l(x) and thus transfers electromagnetic effects from far away to the location of the wave packet.
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Gen Tatara, Hidetoshi Fukuyama
Subject area: Classical and quantum physics: mechanics and fields.
1994 Volume 63 Issue 7 Pages
2538-2562
Published: July 01, 1994
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The macroscopic quantum tunneling of a planar domain wall in a ferromagnetic metal is studied based on the Hubbard model. An effective action of the magnetization for the slowly varying case is obtained to be the same as that of a ferromagnetic Heisenberg model with a term non-local in time that describes the dissipation due to the itinerant electron. The crucial difference from the case of an insulator is the presence of the Ohmic dissipation even at zero temperature due to the gapless Stoner excitation. The dissipative effect is calculated by use of the instanton method, and is found to be very large for a thin domain wall with thickness of a few times the lattice spacing, but is negligible for a thick domain wall. Dissipation due to eddy current is shown to be irrelevant for a wall of mesoscopic size. The results are discussed in the light of recent experiments on ferromagnets with strong anisotropy.
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Hiroaki Nakamura, Minoru Takahashi
Subject area: Statistical physics and thermodynamics.
1994 Volume 63 Issue 7 Pages
2563-2571
Published: July 01, 1994
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A nonlinear susceptibilities (the third derivative of a magnetization m
S by a magnetic field h) of the S=1/2 ferromagnetic Heisenberg chain and the classical Heisenberg chain are calculated at low temperatures T. In both chains the nonlinear susceptibilities diverge as T
-6 and a linear susceptibilities diverge as T
-2. The arbitrary spin S Heisenberg ferromagnet [ H=∑
N_{i=1}, -JS
iS
i+1-(h/S)S
iz, (J>0)] has a scaling relation between m
S, h and T: m
S(T, , h)=F(S
2Jh/T
2). The scaling function F(x)=(2x/3)-(44x
3/135)+O(x
5) is common to all values of spin S.
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Subarna Soheli, Elhamul Hai, Md. A. Rahman, H. M. Sen Gupta, M. Rahman
Subject area: Nuclear reactions and scattering: specific reactions.
1994 Volume 63 Issue 7 Pages
2572-2580
Published: July 01, 1994
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Angular distributions of 17, 20 and 33, MeV tritons scattered elastically from sev-eral nuclei are studied within the framework of the strong absorption model of Frahnand Venter and the best-fit parameter values are obtained. Angular distribution dataof the inelastic scattering of tritons leading to the quadrupole and octupole excita-tions in some nuclei are then studied using the parameters and the correspondingdeformation parameters β
L are extracted.
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Tomoyuki Nagaya, Norihide Fujimoto, Toshihiro Miki, Hiroshi Orihara, Y ...
Subject area: Mechanics, elasticity, and rheology.
1994 Volume 63 Issue 7 Pages
2581-2591
Published: July 01, 1994
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Mechanism of electric conduction in a hydrous electro-rheological fluid has been investigated. Simultaneously with a rheological measurement, an electric current under a sinusoidal electric field was monitored by using a digitizing oscilloscope, and was separated into a conduction current and a displacement current by means of Fourier analysis. It has been found that the conduction current and the viscosity correlate to each other, and the suspension has a nonlinear conductivity, though the silica particle itself has ohmic conductivity. Microscopic observations were also made and the results indicate that the conduction current passes the cluster of particles spanning between the electrodes. On the basis of the experimental results a simple cluster model for the electric conduction is developed, which can explain the correlation between the conduction current and the viscosity, and the nonlinearity of the current response.
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Ryuichi Yokoyama, Hiroaki Gotoda, Kohji Yamamoto, Nobuaki Ikuta
Subject area: The physics of plasmas and electric discharges.
1994 Volume 63 Issue 7 Pages
2592-2601
Published: July 01, 1994
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Electron transport properties in gases, suffering anisotropic scatterings, elastic and inelastic, have been precisely calculated using the Extended FTI method and the Monte-Carlo simulation. Not only the transverse diffusion coefficient which changes with anisotropy in the elastic scattering, the mean energy and the drift velocity have also been found to vary with the degree of anisotropy in the inelastic scatterings. Therefore, it has been understood that the procedures of the Boltzmann equation analyses being currently used to obtain the electron transport properties are strictly valid only under complete isotropy in scatterings.
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Eugene Kotomin, Anatoli Popov, Masamitsu Hirai
Subject area: Lattice dynamics and crystal statistics.
1994 Volume 63 Issue 7 Pages
2602-2611
Published: July 01, 1994
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Theoretical study of the kinetics of the correlated annealing of pairs of close (geminate) F-H centers in KCl and KBr crystals controlled by their diffusion and elastic attraction shows that the multi-step (kink) decay in defect concentrations observed more than once in thermostimulated experiments takes place only for very close F-H center pairs which are no further than fourth nearest neighbors. On the other hand, it is demonstrated (both theoretically and experimentally) that such F-H center pairs should be destroyed by the tunneling recombination already at time ≤ 10
-4, s, i.e. much before beginning of the thermostimulated experiments. Possible explanations of this contradiction are suggested.
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Shik Shin, Yasuhisa Tezuka, Shinji Saito, Yuki Chiba, Mareo Ishigame
Subject area: Equations of state, phase equilibria, and phase transitions.
1994 Volume 63 Issue 7 Pages
2612-2617
Published: July 01, 1994
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Far infrared reflectivity spectra of hydrogen-bonded ferroelectric KH
2PO
4 are measured by using synchrotron radiation in the photon-energy region from 5 to 250, cm
-1. The strong relaxational mode is found in the infrared spectra. This result is consistent with the results which have been obtained by the hyper-Raman and Raman scattering, but inconsistent with the results which have been observed by the ordinary infrared light source.
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Masaki Takesada, Hiroyuki Mashiyama
Subject area: Equations of state, phase equilibria, and phase transitions.
1994 Volume 63 Issue 7 Pages
2618-2626
Published: July 01, 1994
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The mechanism of the α -β transition in K
2ZnBr
4 is investigated by means of an X-ray structural study. The transition is a first-order one accompanied with a large amount of atomic displacements. The relation between the unit cell orientations of α and β phases can not be explained by an ordinal method applicable to the second order phase transition in orthorhombic Rb
2ZnCl
4-group crystals. In order to explain the α -β transition, intermediate body-centered cubic and hexagonal closed-packed structures are considered as virtual states between α and β phases. This virtual intermediate states (VIS) model gives us a good explanation for the change of the cell orientation and also for the large atomic displacements caused by the transition.
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Hiroshi Kontani, Kosaku Yamada
Subject area: Transport properties of condensed matter (nonelectronic).
1994 Volume 63 Issue 7 Pages
2627-2652
Published: July 01, 1994
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The theory of the anomalous Hall effect in the heavy fermion system in the coherent regime is developed on the basis of the periodic Anderson Hamiltonian with degenerate orbitals. The anomalous Hall conductivity arises from the skew-scattering due to the orbital momenta of f-electrons in the presence of magnetic field. By a newly developed analysis based on the phase factor of the f-electron wavefunction in x-y plane, a simple expression for the Hall conductivity σ
xy is derived. It makes possible to understand clearly the mechanism and to estimate the sign and the magnitude of the anomalous Hall coefficient. Our theory explains well experimental results in the heavy fermion systems. Finally, we discuss the extension of this theory to explain the temperature dependence of the Hall coefficient in the cuprate high-T
c superconductors.
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Hironaru Murakami, Syuzo Ohbuchi, Ryozo Aoki
Subject area: Electron states in condensed matter.
1994 Volume 63 Issue 7 Pages
2653-2657
Published: July 01, 1994
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In order to investigate symmetry of the Cooper pairing in high-T
c superconductors, quasiparticle tunneling studies were carried out by means of micro-break SIS junction which was in situ prepared at the LT-STM/STS stage. For La
1.86Sr
0.14CuO
4-x single crystal, a distinct gap structure with a definite bias range of almost zero conductance level was observed on the tunneling spectrum. This result is essentially different from the spectrum predicted by d-wave theories, and rather suggests s-wave superconductivity.
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Takayuki Mizuno, Mikio Eto, Kiyoshi Kawamura
Subject area: Electronic transport in condensed matter.
1994 Volume 63 Issue 7 Pages
2658-2667
Published: July 01, 1994
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Phase shifts are defined for the scattering off an asymmetric potential in a one dimensional space. The Friedel sum rule is derived for such a system, and the resonant tunneling through the asymmetric double-barrier potential is analysed. When the potential goes to symmetric, the newly defined phase shifts do not tend to those defined by Kawabata for the symmetric potential, although the physical quantities expressed in terms of the phase shifts are the same in this limit.
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Yositake Takane
Subject area: Electronic transport in condensed matter.
1994 Volume 63 Issue 7 Pages
2668-2676
Published: July 01, 1994
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Josephson currents in superconductor-normal metal-superconductor junctions are studied numerically when the normal metal region is in the diffusive regime. The average critical current and the fluctuations of the critical current are calculated as a function of the length of the normal metal region L. In the case where L is shorter than the coherence length of the superconductor ξ, the magnitude of the fluctuations is shown to be of order eΔ/(h/2π) (Δ is the pair potential). When L is several times as long as ξ, numerical results suggest that the fluctuations become of order e√ ΔE
c/h(E
c is the correlation energy). These results are compared with previous theoretical studies.
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Richard Lang, Yutaro Okuno, Masuo Fukui
Subject area: Electronic structure and electrical properties of surfaces, interfaces and thin films.
1994 Volume 63 Issue 7 Pages
2677-2684
Published: July 01, 1994
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In a previous publication written by Lang and Fukui, the static electronic charge densities that appear in the immediate vicinity of the Al--Ag and Ag-air interfaces in order to screen surface effects (surface regions referred to as “selvedges”) were assumed to emit supplementary electromagnetic fields when polarised by an incoming light wave. From the calculations, it was predicted that a new structure due to the Ag-air selvedge should appear in the reflection spectra at wavelengths in the 330--350, nm interval. In the present paper, the experimental attenuated total reflection (ATR) frequency scan spectra obtained for various Al--Ag bilayers deposited on prisms in an ultra-high vacuum environment are presented. The expected structure was indeed visible in the spectra of samples that had a thicker silver layer. The experimental results were generally reproducible by using simple Fresnel optics, bulk dielectric constant models and the derived selvedge theory.
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Katsuhiko Nishimura, Junji Sakurai, Katsuhiro Hasegawa, Yoshiaki Saito ...
Subject area: Electronic structure and electrical properties of surfaces, interfaces and thin films.
1994 Volume 63 Issue 7 Pages
2685-2690
Published: July 01, 1994
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The thermoelectric power (thermopower) of a Co/Cu multilayer has been measured in a temperature range from 4.2, K to 270, K. Below 150, K, the thermopower in zero field depends on the sample conditions (as prepared or after applying a saturation field at room temperature) and the direction of a thermal gradient. These results will be discussed in terms of magnetic domain structure.
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Itaru Kobori, Hiroshi Yamaguchi
Subject area: Superconductivity.
1994 Volume 63 Issue 7 Pages
2691-2699
Published: July 01, 1994
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The viscosity of a dilute high temperature superconductor (HTSC) particle suspension in nonconducting liquid is theoretically investigated at temperatures below T
c. Although we have not succeeded in stabilizing the suspension in the region under discussion, the theory predicts that the effective viscosity will increase with external field strength in the domain of H
c1c2. The rotational Brownian motion of the suspended particles is discussed using the Fokker-Planck equation. The resultant formula is applied to Couette flow between two parallel plates.
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Yasuhiro Kawawake, Ko Mibu, Teruya Shinjo
Subject area: Magnetic properties and materials.
1994 Volume 63 Issue 7 Pages
2700-2705
Published: July 01, 1994
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119Sn Mössbauer spectra of Co/Cu multilayers were studied to clarify the role of nonmagnetic layer on the magnetic coupling between ferromagnetic layers. At 300, K, the magnetoresistance (MR) ratio of [Co(20, Å)/Cu(t, Å)]× 8 system shows a maximum value of 17
View full abstract
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Takeshi Hanawa, Kohtaro Shinkawa, Masayasu Ishikawa, Kazuo Miyatani, K ...
Subject area: Magnetic properties and materials.
1994 Volume 63 Issue 7 Pages
2706-2715
Published: July 01, 1994
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We investigated the successive magnetic phase transitions of CoNb
2O
6 at 2.9, K and 1.9, K by measuring the specific heat, magnetic susceptibility and magnetization of poly- and single-crystalline samples. The specific heat measurements performed in external magnetic fields up to about 1.5, kOe disclosed the Ising-like nature of the transitions and tremendous anisotropic magnetic-field dependence due to the low-dimensional character. Moreover, the specific heat and ac magnetic susceptibility data imply another magnetic state below 1, K. These consequences suggest a very interesting magnetic phase diagram, resulting from the competing single-ion anisotropy and exchange interactions in this compound.
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Ichiro Hiromitsu, Shinobu Ohkubo, Jun Yakeuchi, Takashi Ito
Subject area: Magnetic properties and materials.
1994 Volume 63 Issue 7 Pages
2716-2721
Published: July 01, 1994
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Iodine and bromine doped fluoro-aluminum polymer phthalocyanine (AlPcF) thin films are studied by electron spin resonance (ESR). An anomalous g-anisotropy is observed in the ESR spectra of the AlPcF-I
0.1 and the AlPcF-Br
0.3 films in which the resonance frequencies of the spins are averaged to the mean value corresponding to g=(g
⊥ +g
//)/2. The mechanism of the averaging is the spin diffusion along the string-like winding crystallite caused by the exchange interaction. The films after heat treatment do not involve the averaging, and their ESR line widths have the angle dependence of Γ=Γ
0+Γ
1(1+cos
2, θ ), indicating that the exchange interaction is three dimensional. Both the I-doped and the Br-doped films with and without the heat treatment exhibit 3D-antiferromagnetic transition at around 200, K.
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Takashi Nishioka, Koichiro Kimura, Hisayuki Matsui, Masaaki Kontani
Subject area: Magnetic properties and materials.
1994 Volume 63 Issue 7 Pages
2722-2730
Published: July 01, 1994
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The specific heat, magnetic susceptibility and electrical resistivity of uranium-transition-metal binary U-T (T=Os, Ru and Rh) and pseudo-binary URh
1-xT
x (T=Os and Ru) systems are presented. These systems are found to be paramagnets except URh. The electronic specific heat coefficient γ, namely 5f density of states at the Fermi level, increases with the valence d-electron number in order of U--Os, U--Ru and U--Rh systems. URh is perceived to be an itinerant ferromagnet (T
C=55, K) because of the small magnetic entropy associated with the ferromagnetic transition and the small spontaneous magnetic moment at 4.2, K. Substitution of Os and Ru for Rh in URh strongly suppresses the ferromagnetic transition, which fact is qualitatively understood within the framework of the itinerant electron theory.
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Toru Shigeoka, Amalia Garnier, Damien Gignoux, Denys Schmitt, Feng&nda ...
Subject area: Magnetic properties and materials.
1994 Volume 63 Issue 7 Pages
2731-2738
Published: July 01, 1994
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The H-T magnetic phase diagram and field induced magnetic structure in tetragonal DyCo
2Si
2 with a two-step metamagnetic process have been determined by magnetization and neutron diffraction experiments using a single crystal as well as specific heat experiment on a polycrystalline sample. Three magnetic phases exist below T
N=23, K. A simple antiferromagnetic structure (phase I), with the propagation vector Q
1=(0, , 0, , 1) and moments along the c-axis, is stable below 21, K under low field. The intermediate field induced magnetic structure (phase II) is characterized by two additional propagation vectors: i) Q
0=(0, , 0, , 0) and ii) Q
2=(1/2, , 1/2, , 1/2) which is a sub-harmonics of (1, , 1, , 1) (≡ Q
1) and consists of ferromagnetic (111) planes with the sequence of + + + -. It has a resultant magnetization of half the saturation value, i.e. 5.0, μ
B/f.u., at low temperature. Between T
N and 21, K, an antiferromagnetic phase (phase III) with an unknown structure appears.
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Tetsufumi Tanamoto, Hiroshi Kohno, Hidetoshi Fukuyama
Subject area: Magnetic properties and materials.
1994 Volume 63 Issue 7 Pages
2739-2759
Published: July 01, 1994
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The dynamical spin susceptibility, χ (q, , ω ), of the extended t-J model, which reproduces Fermi surfaces of LSCO and YBCO type of high-T
c cuprates, has been evaluated in the slave-boson mean field approximation based on the uniform (u-) and the d-wave singlet (s-) RVB states. The calculated results show reasonable agreement with neutron scattering data for the incommensurate structure in LSCO. For the commensurate structure in 90, K YBCO, the ω -dependence shows general agreement, but the location of the strongest peak at low temperatures does not. The temperature (T) dependences of the rates, T
1-1 and T
G-1, and the shift of NMR are consistent with experimental data in the high-doping region, while they are not in the low-doping (but superconducting) region. We propose that the sharp drop in (T
1T)
-1 above T
c in the low-doping region may be due to singlet formation.
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Chieko Totsuji, Takeo Matsubara
Subject area: Dielectric properties and materials.
1994 Volume 63 Issue 7 Pages
2760-2768
Published: July 01, 1994
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In some substances hydrogen bonds are considered to play an important role in their ferroelectric or antiferroelectric properties. These materials usually have large isotope effects in phase transition temperatures which are expected to be closely related to the natures of hydrogen bonds. Our model describes the quantum mechanics of the electron and the proton (or deuteron) in the 0-dimensional hydrogen bond which does not form networks in the crystal structure. By a variational analyses of this model based on the adiabatic approximation, we can reproduce characteristic features of the behaviors of a proton and a deuteron in hydrogen bonds.
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Katsuhiko Fujii, Hiroki Takeue
Subject area: Dielectric properties and materials.
1994 Volume 63 Issue 7 Pages
2769-2773
Published: July 01, 1994
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The temperature dependence of the spontaneous polarization P
s in the mixed crystal systems [(NH
4)
1-nR
n]
2SO
4 (R=K, Rb, Cs) has been systematically studied by incorporation of a occupation parameter for the R
+ ions, which substitute for the two kinds of crystallographycally nonequivalent ions NH
4+(I) and NH
4+(II). It has been assumed that the variation of lattice constants in each crystal system affects on the interaction constants between ions in a different way, in order to explain that the P
s in the mixed crystal systems changes in a different way with the concentration of R
+ ions. We have described both of NH
4+ and R
+ ions by oscillator model, and used the two sublattice model.
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Shoichi Hirota, Keiichi Edamatsu, Yasuhiro Kondo, Masamitsu Hirai
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1994 Volume 63 Issue 7 Pages
2774-2779
Published: July 01, 1994
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The transient absorption spectra of a self-trapped exciton (STE) localized at iodine dimers (I
22-*) in iodine-doped alkali chloride and bromide crystals (AX:I; A=Na, K, Rb; X=Cl, Br) have been investigated. The absorption bands due to electron-transitions appear below 1, eV, and the bands due to hole-transitions around 1.5 and 3.0, eV. The absorption bands due to the electron-transitions are located in much lower energy region than those of intrinsic STEs in nominally pure alkali chloride or bromide crystals. The bands due to the hole-transitions are very similar to those of V
k (I
2-) centers in alkali iodide crystals. These results suggest that the STE localized at iodine dimers is in the “on-center” configuration and its electronic state is diffused in comparison with that of “off-center” type STE.
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Satoshi Tanaka, Kozo Okada, Akio Kotani
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1994 Volume 63 Issue 7 Pages
2780-2787
Published: July 01, 1994
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The excitation spectrum of the L
3-M
5 X-ray emission of Dy compounds in the pre-edge region of Dy L
3 X-ray absorption near edge structure (L
3-XANES) is theoretically investigated based upon the coherent second order optical formula with multiplet coupling effects. The spectral broadening of the excitation spectrum is determined by the M
5 core hole lifetime, being free from the L
3 core hole lifetime. The fine pre-edge structure of the L
3 edge due to the 2p→ 4f quadrupole transition can be seen in the excitation spectrum, while this structure is invisible in the conventional XANES, in agreement with the recent experimental results. We clarify the conditions for the excitation spectrum to be regarded as the absorption spectrum with a smaller width. The resonant X-ray emission spectra for various incident photon energies around the L
3 edge are also calculated.
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Arata Tanaka, Takeo Jo
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1994 Volume 63 Issue 7 Pages
2788-2807
Published: July 01, 1994
Released on J-STAGE: October 01, 1999
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We present calculated 3d, 3p and 3s resonant photoemission (RPE) spectra in the transition metal (TM) compounds CuO, NiO, CoO, FeO, MnO and TiO
2 at TM 2p core threshold on the basis of a cluster model. Our model includes the intraatomic multipole electron-electron interactions and the hybridization between transition metal ions and ligand. The imaginary part of the self-energy matrix of the intermediate state is calculated by taking into account the 2p3d3d, 2p3d3p, 2p3d3s and 2p3p3p Coster-Kronig decay, which guarantees a sum rule between the integrated RPE spectra and absorption spectra. The dependence of RPE on the incident photon energy tuned to various multiplet structures of TM 2p absorption spectra is shown to be useful to identify the second order optical process, which is argued to include much Auger decay component. It is also shown, by a comparison with experiment, that the present 3d RPE contributes to a removal of discrepancies of estimated parameter values among analyses of other spectra.
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Masaaki Ashida, Riso Kato
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1994 Volume 63 Issue 7 Pages
2808-2817
Published: July 01, 1994
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Temperature dependence of spectral and temporal behaviors of resonant emission in NaNO
2 has been investigated under the excitation of the isotopic level due to
15NO
2- at low temperatures. The emission spectrum consists of series of isotopic, exciton and Raman lines. The sum of the intensities of these lines remains constant up to about 18, K, while those of the isotopic and exciton lines change remarkably above -- 10, K. It is concluded that excitation energy is transferred from the isotopic level to the exciton state mainly by two-phonon scattering process. Time response of the isotopic and exciton lines is interpreted by taking account of the transfer. Spectral change of the exciton line is discussed qualitatively in connection with the thermalization of the excitons within the exciton band.
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Hitoshi Nishimura, Toshio Tsujimoto, Masaaki Nakayama, Takeshi Horiguc ...
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1994 Volume 63 Issue 7 Pages
2818-2824
Published: July 01, 1994
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Pressure induced spectral changes of the σ (4.16, eV), π (3.3, eV) and Ex (3.0, eV) luminescence bands in KI have been observed at 78, K. As hydrostatic pressure is increased, the peak energies of the three luminescence bands shift remarkably to higher energy, and the band widths become narrow. Furthermore, the intensities of the σ and π bands decrease gradually, and that of the Ex band increases slightly. These results are discussed on the basis of a Rabin-Klick ratio and an exciton-phonon coupling strength, depending on hydrostatic pressure.
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Youichi Murakami, Yosuke Watanabe
Subject area: Fluid dynamics.
1994 Volume 63 Issue 7 Pages
2825-2826
Published: July 01, 1994
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Takanao Asahi, Katsuhiko Hasebe
Subject area: Structure of liquids and solids; crystallography.
1994 Volume 63 Issue 7 Pages
2827-2828
Published: July 01, 1994
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Takanori Fukami, Kazuyasu Tobaru, Kazuhito Kaneda, Keiko Nakasone, Kaz ...
Subject area: Structure of liquids and solids; crystallography.
1994 Volume 63 Issue 7 Pages
2829-2830
Published: July 01, 1994
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