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Umesh Chandra Pandey, S. Dev
Subject area: Specific theories and interaction models; particle systematics.
1997 Volume 66 Issue 7 Pages
1853-1855
Published: July 01, 1997
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Majorana neutrino transition magnetic moments [MNTM] in a superstring inspired E
6 model are investigated. The additional fermions in the 27-plet of E
6 are shown to lead to a large enough MNTM for a reasonable choice of Yukawa couplings without imposing the additional `exotic' symmetries prevalent in most other models for large neutrino magnetic moments.
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Kenji Nomura, Naohiko Yasuda, Hidehiro Ohwa, Hikaru Terauchi
Subject area: Equations of state, phase equilibria, and phase transitions.
1997 Volume 66 Issue 7 Pages
1856-1859
Published: July 01, 1997
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Ordered (S=0.8) and disordered (S=0) crystals of PbIn
1/2Nb
1/2O
3 (PIN) were investigated by X-ray diffraction measurement in the temperature range of 20, K to 580, K. The (h/4 k/4 0) superlattice reflection for the ordered antiferroelectric sample and the (h h h) fundamental reflection for the disordered ferroelectric sample were measured for evaluation of the temperature dependence of their order parameters. The (h/2 k/2 0) (α -spots) and the (h/2 0 0) (β -spots) superlattice reflections were also observed. The temperature dependence of the integrated intensity of the α -spot was compared with that of the (h/4 k/4 0) reflection in both samples. Their reflections showed the same temperature dependence. The origin of the α -spots is due to the antiferroelectric distortion. The temperature dependence of the integrated intensity of the α -spot of the ordered sample was different from that of the disordered sample. The differences were explained by a size effect of the clusters.
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Hiroshi Abe, Ryuji J. Matsuo, Mikio Ishibashi, Ken–ichi Ohshima, ...
Subject area: Equations of state, phase equilibria, and phase transitions.
1997 Volume 66 Issue 7 Pages
1860-1863
Published: July 01, 1997
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In metallic sodium, a characteristic waiting time, which is the incubation time until phase transition starts, appears above M
s at a fixed temperature. Small-angle neutron scattering from clusters of the low-temperature phase is observed, which shows good agreement with the aggregation-of-spheres model, whose radius distribution is a Maxwell distribution function. Using the aggregation-of-spheres model, the average radius, r
0, of clusters of the low-temperature phase was found to be 57.2, Å. Moreover, abnormal small-angle neutron scattering from local fluctuations is seen during the waiting time, where this waiting time is related to the nucleation process in the martensitic phase transition.
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Mitsutaka Fujita, Masatsura Igami, Kyoko Nakada
Subject area: Electron states in condensed matter.
1997 Volume 66 Issue 7 Pages
1864-1867
Published: July 01, 1997
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We study the lattice distortion in graphite ribbons of a nanometer width by taking account of the electron-phonon interaction in the tight binding model. In the ribbons with armchair edges, the typical Kekulé structure appears near the edges depending on the distribution of the bond orders. On the other hand, the zigzag ribbons do not undergo bond alternations along the ribbon axis, implying less Peierls instability. Special emphasis is put on the survival of the edge state which forms almost flat bands and a sharp peak in the density of states in consideration of the electron-phonon interaction.
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Satoru Nakatsuji, Shin–ichi Ikeda, Yoshiteru Maeno
Subject area: Electron states in condensed matter.
1997 Volume 66 Issue 7 Pages
1868-1871
Published: July 01, 1997
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Noncuprate layered perovskite Sr
2RuO
4 is a highly correlated metal and exhibits superconductivity below T
c≈ 1.35, K. We have newly synthesized related layered ruthenates Ca
2RuO
4 in two distinct structural phases with substantially different aspect ratios c/a. Electrical and magnetic measurements show that the two phases are insulating antiferromagnets. We argue that both phases of Ca
2RuO
4 are Mott insulators. The decrease of the 4d band width in comparison with that of Sr
2RuO
4, caused by distortions in the RuO
2 planes, leads to a Mott-Hubbard-type gap.
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Yukitoshi Motome, Masatoshi Imada
Subject area: Electron states in condensed matter.
1997 Volume 66 Issue 7 Pages
1872-1875
Published: July 01, 1997
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We present a framework of an auxiliary field quantum Monte Carlo (QMC) method for multi-orbital Hubbard models. Our formulation can be applied to a Hamiltonian which includes terms for on-site Coulomb interaction for both intra- and inter-orbitals, intra-site exchange interaction and energy differences between orbitals. Based on our framework, we point out possible ways to investigate various phase transitions such as metal-insulator, magnetic and orbital order-disorder transitions without the minus sign problem. As an application, a two-band model is investigated by the projection QMC method and the ground state properties of this model are presented.
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Hirokazu Tsunetsugu, Masatoshi Imada
Subject area: Electronic transport in condensed matter.
1997 Volume 66 Issue 7 Pages
1876-1879
Published: July 01, 1997
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The conductivity and Hall coefficient for various types of t-J ladders are calculated as a function of temperature and frequency by numerical diagonalization. A crossover from incoherent to coherent charge dynamics is found at a temperature T
coh. There exists another crossover at T
PG below which a pseudogap opens in the optical spectra, induced by the opening of a spin gap. In the absence of the spin gap, T
coh and the coherent weight are suppressed especially with increasing dimensionality. On the contrary, T
coh is strongly enhanced by the pseudogap formation below T
PG, whereas the coherent Drude weight decreases with increasing dimensionality. The Hall coefficient shows a strong crossover at T
PG below which it has large amplitude for small doping concentration.
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Guo–qing Zheng, Hayato Wakabayashi, Yoshio Kitaoka, Kunisuke Asa ...
Subject area: Superconductivity.
1997 Volume 66 Issue 7 Pages
1880-1883
Published: July 01, 1997
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The
63Cu spin-lattice relaxation rate has been measured in an annealed sample of Tl
2Ba
2Ca
2Cu
3O
10 with T
c=123 K, and compared with that in the previously reported as-grown sample with T
c= 115 K. We found, for the first time, that T
c increases as a result of a decrease in the residual density of states (DOS), N
res, at the Fermi level due to the improvement of crystal ordering by {annealing}. Based on the T
1 result, N
res normalized by the value at T
c, N
res/N
0, was found to be reduced from 0.30 to 0.18 after annealing. A 2-dimensional d-wave superconductivity model accounts for the increase of T
c in terms of the change in potential scattering due to crystal imperfection, which is probably caused by Ca/Tl inter-substitution.
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Noriaki Sato, Naofumi Aso, Gerry H. Lander, Bertrand Roessli, Takemi K ...
Subject area: Superconductivity.
1997 Volume 66 Issue 7 Pages
1884-1887
Published: July 01, 1997
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We have found that there are two contributions to the dynamical response in UPd
2Al
3. The first is a heavily damped spin-wave, which has been observed previously. It shows no appreciable change on warming through T
c, but softens and becomes overdamped as T approaches T
N. The second is a quasielastic-like component that exists in the antiferromagnetically ordered state and is strongly localized around the ordered wavevector. As a function of temperature this component exhibits a minimum at the superconducting transition temperature T
c, and increases strongly below T
c. Its width in the momentum space at T = 0.5, K corresponds to a correlation length of -- 50, Å, which is close to the superconducting coherence length of -- 85, Å.
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Minoru Nohara, Masanobu Isshiki, Hidenori Takagi, Robert J. Cava
Subject area: Superconductivity.
1997 Volume 66 Issue 7 Pages
1888-1891
Published: July 01, 1997
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The low temperature specific heat of the borocarbide superconductor LuNi
2B
2C was measured under various magnetic fields (H) up to 8 T. The coefficient of the T-linear term in specific heat in the mixed state shows marked deviations from the H-linear dependence expected for conventional superconductors and is found to obey a √{H} dependence. A good description of the data can be obtained by assuming the presence of a zero-gap region along lines on the Fermi surface, indicating the possibility of unconventional pairing in the superconducting state of the borocarbides.
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Tatsuya Kawae, Masakazu Ito, Masaki Mito, Masako Hitaka, Kazuyoshi Tak ...
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 7 Pages
1892-1895
Published: July 01, 1997
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We have carried out magnetic susceptibility and heat capacity measurements on a typical Haldane antiferromagnet (CH_3)_4Nni(NO)_3 (TMNIN) doped with nonmagnetic Zn
2+ ion impurities at the concentrations of 7.4%, 11.8% and 20.4% and on a pure system down to 0.2 K. At low temperatures below 1.2 K, the paramagnetic susceptibility expected in the Haldane system with the open chain is found to be suppressed. A broad maximum of the heat capacity is observed around 0.7 K for each impurity system. The observed results strongly suggest that there exists an antiferromagnetic interaction between the edge S=1/2 spins adjacent to Zn
2+ ions via the next-nearest exchange interaction J
nn which can be regarded as a bond impurity in the Haldane system. This is the first experiment on bond impurity models for the Haldane system.
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Hiroyuki Ohsumi, Keisuke Tajima, Nobuyoshi Wakabayashi, Yoshio Shinoda ...
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 7 Pages
1896-1899
Published: July 01, 1997
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An X-ray diffraction study has been made on holmium metal in a magnetic field at several temperatures. In most cases, the c-lattice parameter has been observed to change discontinuously with increasing magnetic field, corresponding to the appearance of various magnetic structures. The result of numerical calculations by a self-consistent mean field method suggests that the effect of the helifan structure on the crystal lattice has been observed in a narrow range of magnetic field.
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Wakako Shiramura, Ken–ichi Takatsu, Hidekazu Tanaka, Kenji Kamis ...
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 7 Pages
1900-1903
Published: July 01, 1997
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High-field magnetization processes of S=1/2 double spin chain systems KCuCl
3 and TlCuCl
3 have been measured up to 39, T at 4.2 and 1.7, K for both systems and at 1.0 and 0.5, K for TlCuCl
3 using single crystals. A transition from a singlet ground state with an excitation gap to a gapless magnetic state with finite susceptibility occurs at H
c-- 20, T and 6, T for KCuCl
3 and TlCuCl
3, respectively. The critical field H
c depends on the external field direction due to the anisotropy of the g-factor. The excitation gap Δ is evaluated as Δ/k
B=31.1, K for KCuCl
3 and 7.5, K for TlCuCl
3. Although the antiferromagnetic interactions in TlCuCl
3 are stronger than those in KCuCl
3, which can be seen from the slope of the magnetization curves above H
c, the excitation gap in TlCuCl
3 is about a quarter of that of KCuCl
3. It is observed that the transition field H
c increases with increasing temperature.
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Fuminori Honda, Tomoko Kagayama, Gendo Oomi, Alexabder V. Andrssv, Lad ...
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 7 Pages
1904-1907
Published: July 01, 1997
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Thermal expansion and magnetostriction of UNiGa single crystal have been measured at the range of pressures up to 2.2, GPa and magnetic fields up to 1.5, T. The results are reported with a special emphasis on anomalies accompanying the magnetic phase transitions and the effect of pressure on the critical parameters (transition temperature and magnetic field). Formation of a new antiferromagnetic phase induced by pressures above 1.8, GPa is revealed. Analysis of results enabled us to construct P-T magnetic phase diagrams for fields up to 1.5, T. The magnetoelastic effects are discussed in terms of marked variations in electronic structure accompanying transitions between different magnetic structures with various couplings of U magnetic moments along the c-axis and involvement of strong spin-orbit interaction.
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Hirotaka Manaka, Isao Yamada
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 7 Pages
1908-1911
Published: July 01, 1997
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We report that antiferromagnetic and antiferromagnetic (AF-AF) alternating Heisenberg chains with S=1/2 are formed in (CH
3)
2CHNH
3CuBr
3, which is in contrast to the almost isomorphous compound (CH
3)
2CHNH
3CuCl
3, because the Cl compound forms ferromagnetic-dominant ferromagnetic and antiferromagnetic (F-AF) alternating Heisenberg chains [H. Manaka et al.: J. Phys. Soc. Jpn. 66 (1997) 564]. From the analysis of the dependence of magnetic susceptibility on temperature, χ(T), the two different antiferromagnetic exchange interactions defined in the Hamiltonian {\cal H}= -2J
1∑ S
2i·S
2i+1 -2J
2∑S
2i·S
2i-1 are determined to be J
1/k=-61 K and J
2/k=-33 K. Applying the low temperature experimental data to the formula χ(T)∝ T
-1/2exp(-Δ/kT), we estimate the energy gap Δ to be 98 K. We discuss why AF-AF and F-AF alternating chains are formed in the Br and the Cl compounds, respectively, in spite of their almost isomorphous crystal structures.
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Weijie Zhang, Jun–ichi Igarashi, Peter Fulde
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 7 Pages
1912-1915
Published: July 01, 1997
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By extending White's density-matrix renormalization group (DMRG) techniqueto finite temperatures, we calculate the impurity susceptibility for the following systems: (a) a spin-1/2 impurity coupled to a single site of an antiferromagnetic Heisenberg spin-1/2 chainand (b) an impurity coupled symmetrically to the two spins atthe open ends of the chain. We also perform a Monte Carlo simulationand show that the DMRG adaptation gives reliable results.The calculated impurity susceptibility showsPauli-like behavior at low temperatures in the former casewhile a ln T divergence is found in the latter case, in agreement with predictions based on conformal field theory.
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Vladimir L. Safonov, Qingfan Shi, Michinobu Mino, Hitoshi Yamazaki
Subject area: Magnetics resonances and relaxations in condensed matter; MÖssbauer effect.
1997 Volume 66 Issue 7 Pages
1916-1919
Published: July 01, 1997
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We considered the process of parametric excitation of spin waves and magnetoelastic waves in magnetoordered crystals in a microwave resonator. From our analysis it follows that for the k and {- k} wave pair there is a single-mode realization (i.e. the pair can be represented as one oscillator). The theory of parametric resonance of waves constructed in terms of these collective variables provides a new perspective on some old spin-wave experiments and helps explain the recently obtained experimental data.
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Naohiko Yasuda, Hidehiro Ohwa, Jun Oohashi, Kenji Nomura, Hikaru Terau ...
Subject area: Dielectric properties and materials.
1997 Volume 66 Issue 7 Pages
1920-1923
Published: July 01, 1997
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The dielectric properties of Pb(In
1/2Nb
1/2)O
3 (abbreviated as PIN) single crystal were investigated under hydrostatic pressures up to 0.7, GPa. The ordered PIN was confirmed to be antiferroelectric by observation of clear P-E double hysteresis loops below the transition temperature. There is a striking pressure effect in the disordered PIN. The relaxor behavior becomes less notable with increasing pressure and disappears at 0.4, GPa. At pressures above 0.4, GPa, the normal phase transition without dielectric dispersion in the low frequency range takes place and with increasing pressure, the temperature T
m, indicating the maximum of the dielectric constant, ε
rm′, increases at a rate of 150, K/GPa and the ε
rm′ decreases. Such dielectric phenomena with pressure are similar to those observed in antiferroelectric PbZrO
3.
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Masatoshi Takeda, Ryuji Tamura, Yoshiko Sakairi, Kaoru Kimura
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1997 Volume 66 Issue 7 Pages
1924-1927
Published: July 01, 1997
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Using the modulated photocurrent method to measure physical properties in the high-structural-quality single-phase icosahedral quasicrystalline alloy Al
70.5Pd
21Re
8.5, we observed photocurrent similar to that in semiconductors in quasicrystals. The observed results were in agreement with those obtained by applying our recently developed photoconductivity model used for boron-rich semiconductors in which band-to-band photoexcitation and photoexcitation from a band to localized states followed by thermal excitation to the conduction band are both considered. Our results confirm the existence of a pseudogap at the Fermi energy E_F and the tendency of carriers to localize near E_F.
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Takashi Nagatani
Subject area: Other areas of research of general interest to physicists.
1997 Volume 66 Issue 7 Pages
1928-1931
Published: July 01, 1997
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A traffic jam induced by slowing down is investigated using the optimal velocity model of the car following models. When cars are decelerated in the presence of hindrances, two kinds of traffic jam occur behind the hindrance: one is an oscillating jam and the other is a homogeneous jam. When the slowing down is small, the oscillating jam occurs. If the slowing down is large, the jam is homogeneous over space and time. The linear stability theory is applied to the traffic jam. The critical line and critical mode of the instability are found. It is shown that the boundary between the oscillating and homogeneous jams is consistent with the critical line of the linear stability. The periods of the oscillating jam are about two times and four times the critical mode estimated by the linear stability theory.
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Kazuhiro Fukushima, Tomoji Yamada
Subject area: Mathematical methods in physics.
1997 Volume 66 Issue 7 Pages
1933-1938
Published: July 01, 1997
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Kink-antikink interaction is numerically studied in a system of a perturbed sine-Gordon equation. We study a system in which a kink and an antikink are localized by placing two impurities between them. The kink and the antikink oscillate chaotically near the impurities by applying the external force. We observe kink-antikink motion with changing the strength of coupling, where the strength of coupling can be changed by changing the distance between two impurities. Time series of the distance between two kinks shows similar characteristics to that in the coupled chaotic oscillator system. An intermittency caused by chaos-chaos interaction is also observed. Power spectrum of this intermittency is a type of 1/f.
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Masato Hisakado
Subject area: Mathematical methods in physics.
1997 Volume 66 Issue 7 Pages
1939-1942
Published: July 01, 1997
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We consider the relation between the discrete coupled nonlinear Schrödinger equation and Toda equation. Introducing complex times we can show the intergability of the discrete coupled nonlinear Schrödinger equation. In the same way we can show the integrability in coupled case of dark and bright equations. Using this method we obtain several integrable equations.
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Masayoshi Tajiri, Yosuke Watanabe
Subject area: Mathematical methods in physics.
1997 Volume 66 Issue 7 Pages
1943-1949
Published: July 01, 1997
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Nonlinear intermitted wave solutions that are recurrent in time are presented to the Boussinesq equation by using the superposition of rational growing modes where the effect of the nonlinearity is taken into account. It is also shown that the breather solution can be constructed by imbricate series of rational growing modes.
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Osamu Tsuchiya, Takashi Yamamoto
Subject area: Mathematical methods in physics.
1997 Volume 66 Issue 7 Pages
1950-1953
Published: July 01, 1997
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The boundary effects in the open Hubbard chain with boundary fields are studied. The boundary string solutions of the Bethe ansatz equations that give rise to a wave functions localized at the boundary and exponentially decreasing away from the boundary are provided. In particular, it is shown that the correct ground state of the model at half-filling contains the boundary 1-strings.
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Yusuke Kato, Takashi Yamamoto, Mitsuhiro Arikawa
Subject area: Classical and quantum physics: mechanics and fields.
1997 Volume 66 Issue 7 Pages
1954-1961
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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We consider the physical properties of elementary excitations of the Calogero-Sutherland (CS) model with SU(K) internal symmetry. From the results on the thermodynamics of this model, we obtain the charge, spin, and statistics of elementary excitations. Combining this knowledge and the known results on the dynamics in the spinless and SU(2) CS models, we propose the expressions for the dynamical correlation functions of the SU(K) CS model. In the asymptotic region, we confirm the consistency of our results with predictions from conformal field theory.
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Michiko Yamana, Hidetoshi Nishimori, Tadashi Kadowaki, D. Sherrington
Subject area: Statistical physics and thermodynamics.
1997 Volume 66 Issue 7 Pages
1962-1975
Published: July 01, 1997
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We develop a systematic expansion method of physical quantities for the SK model and the finite-dimensional ± J model of spin glasses in non-equilibrium states. The dynamical probability distribution function is derived from the master equation using a high temperature expansion. We calculate the expectation values of physical quantities from the dynamical probability distribution function. The theoretical curves show satisfactory agreement with Monte Carlo simulation results in the appropriate temperature and time regions. A comparison is made with the results of a dynamics theory by Coolen, Laughton and Sherrington.
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Taichiro Fukumori, Kenji Imai, Takeo Hasegawa, Yoshito Akashi
Subject area: Measurement science, general laboratory techniques, and instrumentation systems.
1997 Volume 66 Issue 7 Pages
1976-1978
Published: July 01, 1997
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A precision method of measuring the lattice spacing difference by a sensitivity of 1 part in 10
7 is presented. The method uses the Kα doublet from one conventional X-ray tube as two beams with a position sensitive proportional counter in a double-crystal spectrometer. To achieve this sensitivity the device positioning the sample crystal parallel to the monochromator is used. The method is applied to the examination of the lattice spacing variations in silicon crystals containing 0.93 to 1.5× 10
18, atoms/cm
3 of oxygen contents which are subjected to a two-step (low-high) annealing. The lattice spacing differences obtained for these samples are in the range of 10
-7--10
-6.
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Norio Saito, Isao H. Suzuki
Subject area: Atomic spectra and interactions of atoms with photons.
1997 Volume 66 Issue 7 Pages
1979-1985
Published: July 01, 1997
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The yield ratios of triply charged ions to doubly charged ions produced from Xe
+ with 4d
3/2 and 4d
5/2 holes, from Kr
+ with 3d
3/2 and 3d
5/2 holes, and from Ar
+ with 2p
3/2 and 2p
1/2 holes have been measured using a coincidence technique between an energy-selected photoelectron and a charge-specified ion. The difference in the ratios of the double to the normal Auger transitions from the 2p
3/2 and 2p
1/2 hole states in Ar
+ and that in the ratios from the 3d
5/2 and 3d
3/2 hole states in Kr
+ are small. However the difference in those from the 4d
5/2 and 4d
3/2 hole states in Xe
+ is significant. This difference probably originates from the fact that the energy of the ground state of Xe
3+ is just below that of the 4d
5/2 hole state of Xe
+, i.e., the difference in the excess energy and the number of available states play a critical role in the transition.
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Takasi Endo, Eitaro Morimoto, Yutaka Hirayoshi, Kouich Toyoshima
Subject area: Optics.
1997 Volume 66 Issue 7 Pages
1986-1988
Published: July 01, 1997
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Photocurrent noise from an LED is measured as a function of the current source impedance. Bandwidth of noise reduction is found to be equal to the inverse of the time constant which is the product of the differential resistance of the LED and a paralelly connected capacitance. The experimental results are described in terms of a simple equivalent circuit.
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Hong–Chen Fu, Ryu Sasaki
Subject area: Optics.
1997 Volume 66 Issue 7 Pages
1989-1994
Published: July 01, 1997
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We introduce the negative binomial states with negative binomial distribution as their photon number distribution. They reduce to the ordinary coherent states and Susskind-Glogower phase states in different limits. The ladder and displacement operator formalisms are found and they are essentially the Perelomov's su(1,1) coherent states via its Holstein-Primakoff realization. These states exhibit strong squeezing effect and they obey the super-Poissonian statistics. We discuss two methods to generate these states.
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Katsuya Ishii, Shizuko Adachi, Sadao Akishita
Subject area: Fluid dynamics.
1997 Volume 66 Issue 7 Pages
1995-2001
Published: July 01, 1997
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The sound pressure level is computed using the Lighthill-Curle theory for the far-field acoustic pressure excited by flow around solid bodies. Time evolution of the flow field is obtained by solving the three-dimensional compressible Navier-Stokes equation with a block pentadiagonal matrix scheme based on the approximate factorization method. The far-field sound pressure level is evaluated from the fluctuation of the pressure on a wing surface. Numerical simulation is done for a NACA-0015 airfoil at the attack angle of 8°in a subsonic flow. The computed results are compared successfully with the experimental data. The surface dipole strength density is estimated to show which regions in space dominantly contribute to prominent peaks in the sound pressure level. We discuss the three-dimensional effect by comparing the results from the three- and two-dimensional computation.
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A. M. El–Hanbaly, A. Elgarayhi
Subject area: Kinetic and transport theory of fluids; physical properties of gases.
1997 Volume 66 Issue 7 Pages
2002-2007
Published: July 01, 1997
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By means of the Lie group approach the symmetry of Vlasov-Fokker Planck equation (VFPE) with an arbitrary electric field of space and time are found. Mathematical forms are obtained for the electric field permit symmetry. Maxwell's equations are then used to constrain the solution further. Finally, we obtain a complete classification of all possible nontrivial similarity solutions of the VFPE plus Maxwell equations.
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Masanori Takaoka
Subject area: Kinetic and transport theory of fluids; physical properties of gases.
1997 Volume 66 Issue 7 Pages
2008-2025
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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Anisotropy and vortex structures in turbulence subjected to mean uniform strain are investigated by a direct numerical simulation of the incompressible Navier-Stokes equation. Three types of irrotational homogeneous straining flows are examined as a mean flow: plane strain, axisymmetric contraction and axisymmetric expansion. The imposed mean straining flow produces turbulence energy and does so by preferentially inducing the anisotropy in large length scale. The skewness and the flatness of velocity derivatives are also calculated for the conditionally sampled data classified according to vorticity magnitudes, which reveals the role of vortex structure in their deviations from a Gaussian random field. Anisotropy in each length scale is examined in Fourier space. By using the relation of the one-dimensional lateral and longitudinal energy spectra we find that the field becomes isotropic with smaller length scale, though the large length scale structures inherit anisotropy. Our numerical results suggest a phenomenological model of `hierarchic vortex structure'.
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Kentaro Yabuki, Kunihiko Watanabe, Tetsuya Sato
Subject area: The physics of plasmas and electric discharges.
1997 Volume 66 Issue 7 Pages
2026-2032
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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In order to examine the role of the energy input in the formation of an ordered structure in a semi-open system, we have developed a nonlinear simulation model in which the energy input time and the dynamic response time of the system are changeable. For this purpose, a viscous membrane (boundary layer) is placed between a steady convection source and a nonlinear feedback system in which a dissipation-free magnetohydrodynamic plasma and a resistive weakly-ionized plasma are coupled. It is found that the thin viscous membrane acts to be a high-pass filter that can play a role of a fixed boundary for the dc component but a free boundary for the ac component. Because of this character of the membrane, when the ratio of the ac energy input time to the dynamic response time of the system becomes relatively large, the membrane acts to release the fluctuation (ac) energy from the system. Consequently, the positive feedback effect for the fluctuation is weakened and the structure formation is prevented as the ratio exceeds a certain critical value. It is also found that the viscous membrane plays another important role in self-organization, namely, that as the structure formation is highly progressed, the dc energy input rate is autonomously adjusted so as to keep the developed structure in a steady form.
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Yuji Kurimoto, Hideki Zushi, Fumimichi Sano, Katsumi Kondo, Toru Mizuu ...
Subject area: The physics of plasmas and electric discharges.
1997 Volume 66 Issue 7 Pages
2033-2043
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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In the Heliotron E device, combining a neutral beam injection (NBI) with an electron cyclotron resonance heating (ECRH) system, new physical issues are applied to the investigation of fast ion behavior. Especially, the slowing-down (deceleration and parallel diffusion) and the loss processes are studied experimentally through measurements of the temporal change of charge-exchange neutral particle energy spectra. As results, first, in the longer slowing-down time (τ
s -- 200 ms) plasma realized by ECRH, discrepancies from the theoretical values are detected in the deceleration and the parallel diffusion processes, whose factors are 4--6 for the former, 6--13 for the latter. Second, the fast ion loss cone is reduced by the ECRH on the NBI plasma, of which cause is discussed associated with the modification of the radial electric field, E
r.
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Shinji Nakazawa, Yukiharu Ohsawa
Subject area: The physics of plasmas and electric discharges.
1997 Volume 66 Issue 7 Pages
2044-2050
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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The structure of nonlinear magnetosonic waves with relativistic propagation speeds is studied through theory and particle simulation. First, the maximum values of magnetic and transverse electric fields and electric potential are analytically obtained as a function of the Alfvén speed and Mach number, under the assumption that waves propagate nearly steadily in the direction perpendicular to a magnetic field. Then, one-dimensional, relativistic, electromagnetic particle code with full ion and electron dynamics is used to study relativistic magnetosonic waves. It is found that the ion currents parallel to the the wave front become comparable to the electron currents in magnitude. As the propagation speed is increased, transverse fields become dominant components in electromagnetic fields of a wave. The theoretically obtained values of field quantities are in good agreement with the simulation results.
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Ryoichi Minai, Isao Katanuma, Teruo Tamano
Subject area: The physics of plasmas and electric discharges.
1997 Volume 66 Issue 7 Pages
2051-2056
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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We investigate the ion axial confinement time and the ion endloss spectrum in a wide range of collision frequency in a tandem mirror by using Monte-Carlo simulation. It is found that the ion endloss spectrum and the effective temperature determined from the spectrum have a transition depending on the collision frequency. Particularly, in cases where the collision frequency is low, the effective temperature deviate from the field temperature.
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Mitsuaki Ginoza, Makoto Yasutomi
Subject area: Structure of liquids and solids; crystallography.
1997 Volume 66 Issue 7 Pages
2057-2062
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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The solvent-mediated force between colloidal particles in a liquid is studied with the use of the model system consisting of the solvent spheres and the solute spheres (colloidal particles): spheres interact through Yukawa-type potentials with different damping factors. The study is based on the mean spherical approximation solution of the Ornstein-Zernike equation with the closure of three Yukawa terms. In the case of the lyophobic solute in the dilute limit, the dependence of the solvent-mediated force on the interaction between solvent spheres is investigated in relation to the exponential decay nature of the force measured in the range shorter than about 15 nm. The result is consistent with the experimental one.
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Makoto Fuchigami, Kazuyuki Itoh
Subject area: Structure of liquids and solids; crystallography.
1997 Volume 66 Issue 7 Pages
2063-2067
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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We determined the crystal structure of RbDSO
4 in the paraelectric phase by X-ray diffraction study. The structure is isomorphous to the paraelectric structure of undeuterated RbHSO
4. There are two kinds of RbDSO
4 molecules in the unit cell. One of the SO
4 ions takes disordered molecular arrangements. Both kinds of the D atoms are located acentrically in the hydrogen bonds and combine the ordered and disordered SO
4 ions, respectively. The D atom combining the disordered SO
4 ion executes very large thermal vibrations and its nature can be understood by the riding model, in which the D atom displaces in phase with the disordered motion of the closer SO
4 ion.
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Hirosi Okamoto
Subject area: Electron states in condensed matter.
1997 Volume 66 Issue 7 Pages
2068-2074
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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A renormalization group treatment is applied to a model of (quasi)-two-dimensional semiconductor with a small band gap. Phase diagrams are derived based on the numerical solutions of the scaling equations. In the purely two-dimensional case, we find the singlet superconducting phase is induced by the repulsive interband interaction in the presence of the attractive intraband interaction. We also find the ferromagnetism and/or the ferroelectricity are stabilized in the presence of the repulsive interband and intraband interactions. The effects of the other kinds of interband and interplanar interactions are also discussed.
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Koichi Kusakabe
Subject area: Electron states in condensed matter.
1997 Volume 66 Issue 7 Pages
2075-2085
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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The extended spectral flow at the normal-superconducting transition is investigated for the one-dimensional Hubbard model. Recombination of spectral flow lines at U=± 0, which causes halving of the extended Aharonov-Bohm period for U<0 found in a recent paper [K. Kusakabe and H. Aoki: J. Phys. Soc. Jpn. 65 (1996) 2772], is exactly analyzed using the Bethe ansatz solution. Adiabatic motion of charge rapidities which are real for U>0 (normal Luttinger liquid) or complex for U<0 (superconducting Luther-Emery liquid) dominates sudden response of the spectral flow at the transition point. The extended period is obtained not only against the charge flux but also against the spin flux for both U>0 and U<0.
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Ryotaro Arita, Koichi Kusakabe, Kazuhiko Kuroki, Hideo Aoki
Subject area: Electron states in condensed matter.
1997 Volume 66 Issue 7 Pages
2086-2096
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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The `extended Aharonov-Bohm (AB) period' recently proposed by [K. Kusakabe and H. Aoki: J. Phys. Soc. Jpn. 65 (1996) 2772] is extensively studied numerically for finite size systems of strongly correlated electrons. While the extended AB period is the system length times the flux quantum for noninteracting systems, we have found the existence of the boundary across which the period is halved or another boundary into an even shorter period on the phase diagram for these models. If we compare this result with the phase diagram predicted from the Tomonaga-Luttinger theory, devised for low-energy physics, the halved period (or shorter periods) has a one-to-one correspondence to the existence of the pairing (phase separation or metal-insulator transition) in these models. We have also found for the t-J model that the extended AB period does not change across the integrable-nonintegrable boundary despite the totally different level statistics.
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Kazutomo Suenaga, Christian Colliex, Catherine Sant, Sid Labdi, Philip ...
Subject area: Electronic structure and electrical properties of surfaces, interfaces and thin films.
1997 Volume 66 Issue 7 Pages
2097-2102
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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Compositionally modulated TiN
x multilayers (0.3
3 peak, so-called white line, broadens in accordance with the nitrogen concentration, due to a change in the d band occupation. A shift of the volume plasma frequency towards lower energies when the nitrogen vacancy concentration increases is observed and explained in terms of a simple free-electron gas model. These results demonstrate the great power of spatially resolved electron energy loss spectroscopy as a probe of electronic structure with subnanometer-scale spatial resolution.
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Atsuo Isobe, Masaaki Yamada, Kazuhide Tanaka
Subject area: Electronic structure and electrical properties of surfaces, interfaces and thin films.
1997 Volume 66 Issue 7 Pages
2103-2109
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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The Ni_xSi
100-x system forms a homogeneous amorphous phase over wide ranges of composition (0≤ x≤ 34 and 63≤ x≤ 73) when the alloy is deposited on a substrate by sputtering at ambient temperature. The electrical conductivity of the amorphous alloy changes characteristically with Ni concentration from a semiconductor-like temperature dependence to a metallic one, the transition taking place between 10.4 and 16.6% Ni. UPS valence band spectra show that the density of states at the Fermi level is minimal below about 7% Ni, but emerges abruptly above this concentration. The relationship between the electrical transport properties and the electronic structure of the amorphous alloys is discussed in three characteristic regions of the Ni concentration.
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Hikaru Kawamura, Mai Suan Li
Subject area: Superconductivity.
1997 Volume 66 Issue 7 Pages
2110-2122
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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Possible occurrence of an equilibrium thermodynamic phase with a spontaneously broken time-reversal symmetry is studied in a model ceramic superconductor with anisotropic pairing symmetry. It is shown by Monte Carlo simulations that such a “chiral-glass” phase is truly stable even under the influence of screening. Existence of frustration in zero external field, arising from the d /-wave pairing symmetry of high-T
c superconductors, is essential to realize this phase. Via a finite-size scaling analysis, critical exponents associated with the chiral-glass transition are estimated to be ν
CG=1.3± 0.2 and η
CG=-0.2± 0.2. These values turn out to be close to those of the Ising spin glass. Phase diagram of the model is constructed and the implications to experiments are discussed.
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Yuuki Watanabe, Seiji Miyashita
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 7 Pages
2123-2128
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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We investigate the magnetization of the ground state of the one-dimensional flat-band Hubbard model as a function of the electron filling, using exact diagonalization techniques. Our calculation shows that the systems with odd n holes added to half-filling bands for a sufficiently large U (the on-site Coulomb repulsion energy) have a saturated ferromagnetic ground state, which is nondegenerate except for the trivial spin degeneracy. Dependences of the critical value of U on the size and on λ (a parameter of the system) are also investigated. For all values of λ, it is found that the ground state is a saturated ferromagnetic state if U is sufficiently large. Moreover, we find that the critical U for the saturated ferromagnetic ground state is almost independent on the system size, at least, for the system near quarter-filling. These facts indicate that even if the system size go to infinity, the ferromagnetic ground state can be exist for a finite U.
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Takuya Okabe
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 7 Pages
2129-2132
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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We derive expressions required in generalizing the Gutzwiller approximation to models comprising arbitrarily degenerate localized orbitals.
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Kazunori Umeo, Toshiro Takabatake, Noriaki Sato, Takemi Komatsubara, K ...
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 7 Pages
2133-2137
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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We report on the magnetic, transport, and thermal properties of a heavy-fermion antiferromagnet Ce
7Ni
3. The Ce ions in the three nonequivalent sites are found to be very close to trivalent from L
III X-ray absorption spectroscopy and magnetic susceptibility measurements. The magnetic susceptibility along the c axis exhibits a pronounced peak at the Néel temperature T
N=1.9, K, while that along the b axis defined perpendicular to the a axis shows a rounded maximum at 0.6, K. The magnetization curve for B//c at 1.4, K exhibits a metamagnetic transition at 0.2, T, and reaches a value of 1.0, μ
B/Ce at 36, T. The electrical resistivity ρ (T) for I//c turns up below T
N, whereas those for I//a and I//b decrease. These results suggest that the antiferromagnetic order creates a partial gap along the c axis on the Fermi surface. The magnetic entropy due to 4f electrons reaches 0.47R ln 2 at T
N. The magnetic moment and magnetic entropy in the antiferromagnetic state are substantially reduced by the combination of the Kondo effect and crystalline electric field (CEF) effect. The Kondo temperature and energy of the first CEF level are estimated to be 7, K and 240, K, respectively, by the analysis of the specific heat.
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Junya Sasaki, Fumitaka Matsubara
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 7 Pages
2138-2146
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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We make a large-scale Monte Carlo (MC) simulation of a ferromagnetic Heisenberg model with dipolar interactions on a two-dimensional square lattice L× L with open boundaries. We find that, as L is increased, the spin structure changes from a ferromagnetic one to a novel one characterized by a circular arrangement of spins. We suggest that, in the thermodynamic limit, a long-range circular phase occurs in the cooperation of the exchange and the dipolar interactions and that the phase transition between the paramagnetic phase and the circular phase is of the second order. In this study, we develop a discrete update MC method which reduces the CPU time from of the order N^2 to Nlog_2N per one MC sweep, where N is the number of the spins.
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Masaki Mito, Hiroyuki Nakano, Tatsuya Kawae, Masako Hitaka, Seishi Tak ...
Subject area: Magnetic properties and materials.
1997 Volume 66 Issue 7 Pages
2147-2156
Published: July 01, 1997
Released on J-STAGE: October 01, 1999
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A genuine organic radical crystal 1, 3, 5-triphenyl-6-oxoverdazyl (TOV) has been revealed to be an S=1/2 two-dimensional (2D) weak-ferromagnetic Heisenberg antiferromagnet with the exchange interaction 2J/k
B=-9.0, K by the experiments of magnetic susceptibility, heat capacity, magnetization and electron paramagnetic resonance. The anomalous temperature dependence of the weak ferromagnetism at low temperatures is qualitatively explained by a four-sublattice model with two kinds of Dzyaloshinsky-Moriya (D-M) vectors of opposite sign on the ac-plane. The staggered susceptibility, which is a fictitious but intrinsic quantity for antiferromagnets, is estimated in TOV by making use of the canted weak ferromagnetic moments which dominate below 6, K. Especially the rapid growth of the magnetic susceptibility below 6, K is explained by the staggered susceptibility which makes the crossover effect from 2D Heisenberg to 2D Ising system, triggered by above the D-M anisotropy.
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