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Sadakane Tomoyuki
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1441-1443
Published: 2001
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Multisoliton solutions of the semi-discrete and full-discrete versions of the Landau-Lifshitz equation are constructed explicitly by means of the elliptic version of Zakharov's dressing method developed by Cherednik.
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Izumi Tomeno, Senji Shimanuki, Yorihiko Tsunoda, Yoshinobu Ishii
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1444-1447
Published: 2001
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Inelastic-neutron-scattering experiments were performed to investigate the phonon-dispersion relations in the cubic relaxor Pb(Zn
1/3Nb
2/3)O
3. The transverse acoustic (TA) phonon branches have flat and isotropic dispersion curves. The zone-boundary [ζ ζ 0]-TA
2 phonon energy is approximately 6 meV, considerably lower than the values reported for simple perovskites. The low-lying transverse optical (TO) branches drop sharply with decreasing ζ, similar to the behavior observed for the complicated system Pb(Zn
1/3Nb
2/3)
0.92Ti
0.08O
3. The constant-Q scans reveal the absence of the well-defined TO phonon spectra in the range 0≤ ζ ≤ 0.1, in contrast with the sharp TA spectra. The TA, TA
2 and TO phonon energies at ζ =0.1 and 0.2 decrease with increasing temperature up to 673 K. The phonon hardening toward the transition temperature contradicts the usual soft mode behavior in simple perovskites.
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Kazutaka Kudo, Takashi Noji, Yoji Koike, Terukazu Nishizaki, Norio Kob ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1448-1451
Published: 2001
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We have measured the thermal conductivity of the two-dimensional spin-gap system SrCu
2(BO
3)
2 single crystal in magnetic fields up to 14 T. In zero field, both the in-plane and out-of-plane thermal conductivities exhibit anomalous enhancement at low temperatures below ∼ 11 K. The enhancement is suppressed with increasing magnetic field. The enhancement in zero field is attributed to the increase of the thermal conductivity due to phonons, which is caused by the suppression of the phonon-magnon scattering owing to the spin-gap formation. The suppression of the enhancement by the application of magnetic field is explained by the reduction of the spin gap.
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Sheng Zhong, Mu Wang, Xiao-Bo Yin, Jian-Ming Zhu, Ru-Wen Peng, Yuan Wa ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1452-1455
Published: 2001
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Straight copper wire arrays are electrochemically deposited on a silicon substrate without utilizing additives or templates. To suppress the influence of the factors which arouse the ramification of the copper electrodeposit, an ultrathin electrochemical deposition system and an initially homogeneous electric field are used. The width of the copper wires may vary from about 200 nm to about 1.5 μm depending on the control parameters. The microstructure of the copper wires and their electric resistance after vacuum-annealing at 200
ºC are studied. We suggest that this self-organized copper electrodeposition is helpful in gaining an understanding of the formation of dense-branching morphology. It also implies the potential application in microelectronics.
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Ken-ichiro Matsuno, Takuro Katsufuji, Shigeo Mori, Yutaka Moritomo, Ak ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1456-1459
Published: 2001
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We have found that spinel AlV
2O
4 shows a phase transition at ∼700 K with anomalies of transport and magnetic properties. It is clarified that this corresponds to a charge-ordering transition, where the V
2.5+ ions are separated into three V
2.5-δ ions and one V
2.5+3δ ion. This three-one type of charge ordering, which is coupled with rhombohedral distortion along the (111) axis, reduces the high degeneracy of ground states inherent in this spinel structure, and thus can be understood in terms of “charge frustration.”
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Masahisa Tsuchiizu, Hideo Yoshioka, Yoshikazu Suzumura
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1460-1463
Published: 2001
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The interplay between quarter-filled and half-filled umklapp scattering has been examined by applying the renormalization group method to a one-dimensional quarter-filled electron system with dimerization, on-site (U) and nearest-neighbor (V) repulsive interactions. The phase diagram on the U-V plane is obtained at absolute zero temperature where the Mott insulator (the charge ordered insulator) is found for smaller (larger) V. By choosing the moderate parameter in the region of Mott insulator, it is shown that the resistivity exhibits a crossover from behavior of quarter-filling to that of half-filling with decreasing temperature.
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Jinhee Kim, Kicheon Kang, Jeong-O Lee, Kyung-Hwa Yoo, Jae-Ryoung Kim, ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1464-1467
Published: 2001
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The electrical transport properties of two multiwall carbon nanotubes in a crossed geometry were studied. Each carbon nanotube exhibited differential conductance vanishing with the power of bias voltage. The power-law dependence of the differential conductance was attributed to the Tomonaga-Luttinger liquid behavior of the carbon nanotube, which is considered to be a one-dimensional conductor. The differential conductance curve of one of the two carbon nanotubes was affected significantly by constant bias voltage applied to the other carbon nanotube. The characteristic features of the change of the differential conductance curve we have observed are in good agreement with the theoretical predictions for the two crossed Tomonaga-Luttinger liquids which are expected to exhibit correlated electron transport.
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Hiroshi Akera
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1468-1471
Published: 2001
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The hydrodynamic equation for the spatial and temporal evolutions of the electron temperature T
e in the breakdown of the quantum Hall effect at even-integer filling factors in a uniform current density j
x is derived from the Boltzmann-type equation, which takes into account electron-electron and electron-phonon scattering processes. The derived equation has a drift term, which is proportional to j
x and the first spatial derivative of T
e. When applied to the spatial evolution of T
e in a sample with an abrupt change of the width along the current direction, the equation gives a distinct dependence on the current direction as well as a critical relaxation, in agreement with results of recent experiments.
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Takao Morinari
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1472-1475
Published: 2001
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We show that a Chern-Simons term for a gauge field describing a fluctuation of spins is induced by integrating out hole fields in the presence of spin-orbit coupling which originates from a buckling of the CuO
2 plane. Through the Chern-Simons term, holes behave like skyrmion excitations in a spin system and become a superconducting state with d
x2-y2 symmetry after the antiferromagnetic long-range order is destroyed.
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Kunihiko Yamaji
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1476-1479
Published: 2001
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Using the tight-binding method for the π-bands in MgB
2, the Hubbard on-site Coulomb interaction on two inequivalent boron p
z-orbitals is transformed into expressions in terms of π-band operators. For scattering processes relevant to the problem in which a wave vector q is parallel to ˆz, it is found to take a relatively simple form consisting of intra-band Coulomb scattering, interband pair scattering etc. with large constant coupling constants. This allows to get a simple expression for the amplitude of interband pair scattering between two π-bands, which diverges if the interband polarization function in it becomes large enough. The latter was approximately evaluated and found to be largely enhanced in the band structure in MgB
2. These results lead to a divergent interband pair scattering, meaning two-band-type superconducting instability with enhanced T
c. Adding a subsidiary BCS attractive interaction in each band into consideration, a semi-quantitative gap equation is given, and T
c and isotope exponent α are derived. The present instability is asserted to be the origin of high T
c in MgB
2.
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Takahiro Muranaka, Serena Margadonna, Isabelle Maurin, Kierin Brigatti ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1480-1482
Published: 2001
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Neutron inelastic scattering measurements have been performed on superconducting MgB
2 above and below T
c. The temperature dependence of the generalized phonon density-of-states showed clear anomalous behaviour near 24 meV in the acoustic phonon region, which may be interpreted as evidence of a substantial contribution to the total electron-phonon coupling strength deriving from these phonons. Weaker evidence for a corresponding response in the high-energy B bond stretching phonons was also encountered.
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Nobuo Furukawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1483-1486
Published: 2001
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As a model for the B 2p
z bands of MgB
2, a half-filled Hubbard model on a honeycomb lattice is studied, and a possibility of an antiferromagnetism (AF) at the ground state is examined by Monte Carlo calculations as well as a random phase approximation method. On a single-layer honeycomb lattice, a paramagnetic to AF phase transition occurs at a finite value of the repulsion energy U
c/t ∼eq 3.6, due to the loss of the density of states at the fermi level. On a layered honeycomb lattice, however, inter-layer hopping term creates a perfect nesting of the fermi surface, and leads the AF with U
c=0. From these facts, we discuss that MgB
2 is possibly a nearly-AF metal, where the AF of the 2p
z bands is destroyed by carrier doping.
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Yukitoshi Motome, Nobuo Furukawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1487-1490
Published: 2001
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Critical phenomena of ferromagnetic transition at finite temperatures are studied in double-exchange systems. In order to investigate strong interplay between charge and spin degrees of freedom, the Monte Carlo technique is applied to include fluctuations in a controlled and unbiased manner. By using finite-size scaling analysis, critical exponents and transition temperature are estimated for a model with Ising spin symmetry in two dimensions. The obtained exponents differ significantly from the mean-field values, but are consistent with those of spin models with short-range exchange interactions. The universality class of this transition belongs to that of short-range interaction with the same spin symmetry. We also discuss the case for three dimensions. The results are compared with experimental results in perovskite manganites which show colossal magnetoresistance.
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Takateru Kawakami, Saburo Nasu, Tetsuya Sasaki, Syotaro Morimoto, Shoi ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1491-1494
Published: 2001
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Using a diamond anvil cell,
57Fe Mossbauer spectroscopy has been carried out on the perovskite oxide CaFeO
3 under high pressures up to 65 GPa at various temperatures. The critical temperature of a charge disproportionation (CD: 2Fe
4+ → Fe
3+ + Fe
5+) and a magnetic ordering have been determined as a function of pressure. The CD occurs at an almost constant temperature of about 290±3 K in the pressure range of 0-17 GPa. At an increase of the pressure above 20 GPa, the CD reaction is suppressed and its critical temperature reduces to lower than 6 K. On the other hand, the magnetic ordering temperature of 125 K at an ambient pressure rises to 400 K at 34 GPa without the CD, which suggests that the different charged particles control the charge and spin order separately in CaFeO
3.
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Koichi Kindo, Sachie Ookita, Yasutomo Sasaki, Takaya Matsukawa, Asako ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1495-1497
Published: 2001
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The magnetic susceptibility of the non-heme iron in plant photosystem II was first measured by a highly sensitive magnetometer equipped with a pulsed magnetic field. From the temperature dependence of the paramagnetic susceptibility of the non-heme ferrous iron with S=2, the zero-field interaction parameters D and E were determined to be 5.5± 1.0 and 0.75± 0.75 cm
-1, respectively. These values are almost the same as those observed in a purple photosynthetic bacterium
Rhodobacter sphaeroides, suggesting that the structure of the acceptor side of plant photosystem II is also similar to that of the purple photosynthetic bacterium.
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Hang-Yu Ruan, Yi-Xin Chen
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1499-1504
Published: 2001
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In this paper, a variable separation approach is used to study the localized coherent structures of the (2+1)-dimensional generalized Nizhnik-Novikov-Veselov (GNNV) equation. The abundance of the localized structures of the model is introduced by the entrance of two variables separated arbitrary functions. For some special selections of the arbitrary functions, it is shown that the localized structures of the GNNV equation may be dromions, breathers, instantons and ring solitons etc.
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Masayoshi Tajiri, Kiyohiro Takeuchi, Takahito Arai
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1505-1511
Published: 2001
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The stability of soliton of the Davey-Stewartson I equation is discussed by the Hirota method. A close relation exists between the periodic soliton resonance and the soliton instability to the transverse disturbances. It is shown that the solutions of periodic soliton resonance describe the nonlinear stage of the instability.
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Takeya Tsurumi, Miki Wadati
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1512-1518
Published: 2001
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Ground state properties of a toroidally trapped Bose-Einstein condensate are investigated analytically. Through the variational approach, effects of the geometrical curvature and the inter-atomic interaction are taken into consideration. It is shown that the curvature lowers the ground state energy, and that the condensate is attracted towards the axis of symmetry of the torus.
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Hans-Georg Matuttis, Nobuyasu Ito
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1519-1522
Published: 2001
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The quantum Monte Carlo method for the Hubbard model using the Hubbard-Stratonovich transformation is reexamined. It is observed that the value of the ground state energy for a 3× 2 and 4× 4 system is estimated correctly by ignoring the minus-sign of the negative sampling weight appearing in the simulation using the projector method. It is also observed that the average of sign is positive and the correlation between the energy and the sign is weak for these systems. The reasons why the ground state energy is estimated correctly is given on a phenomenological base.
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Miyuki K. Shimamura, Tetsuo Deguchi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1523-1536
Published: 2001
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We discuss the entropy of a circular polymer under a topological constraint. We call it the
topological entropy of the polymer, in short. A ring polymer does not change its topology (knot type) under any thermal fluctuations. Through numerical simulations using some knot invariants, we show that the topological entropy of a stiff ring polymer with a fixed knot is described by a scaling formula as a function of the thickness and length of the circular chain. The result is consistent with the viewpoint that for stiff polymers such as DNAs, the length and diameter of the chains should play a central role in their statistical and dynamical properties. Furthermore, we show that the new formula extends a known theoretical formula for DNA knots.
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Hiroshi Watanabe, Satoshi Yukawa, Nobuyasu Ito, Chin-Kun Hu, Chai-Yu L ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1537-1542
Published: 2001
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We derive an equation for the existence probability E
p for general percolation problem using an analytical argument based on exponential-decay behaviour of spatial correlation function. It is shown that the finite-size scaling function is well approximated by the error function. The present argument explain why it is universal. We use Monte Carlo simulation to calculate E
p for polydisperse continuum percolation and find that mono- and polydisperse system have the same finite-size scaling function.
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Shin-ichi Endoh, Fumitaka Matsubara, Takayuki Shirakura
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1543-1548
Published: 2001
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We examine the stiffness of the Heisenberg spin-glass (SG) model at both zero temperature (T=0) and finite temperatures (T ≠ 0) in three dimensions. We calculate the excess energies at T=0 which are gained by rotating and reversing all the spins on one surface of the lattice, and find that they increase with the lattice size L. We also calculate the excess free-energies at T ≠ 0 which correspond to these excess energies, and find that they increase with L at low temperatures, while they decrease with increasing L at high temperatures. These results strongly suggest the occurrence of the SG phase at low temperatures. The SG phase transition temperature is estimated to be T
SG ∼ 0.19J from the lattice size dependences of these excess free-energies.
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Kenji Oda, Takahiko Miyakawa, Hiroyuki Yabu, Toru Suzuki
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1549-1555
Published: 2001
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The s-wave scattering parameters for the Positronium-Positronium (Ps-Ps) interaction are estimated semi-phenomenologically with the long-range van der Waals force and the short-range repulsive potential. The obtained values of the scattering length and the effective range are a ∼ 0.44 nm, and r
0 ∼ 0.2 nm for the symmetric channel. Stability of them is also checked with two kinds of potential with different parametrizations. Spin coupling schemes for the Ps-Ps system are discussed and the formulae of scattering length for each spin channel are derived. Using this value of the scattering length, the Gross-Pitaevskii equation can be fixed for the Positronium Bose-Einstein condensates (Ps BEC). The static properties of Ps BEC are discussed using the solutions of that equation. The critical temperature shift of the phase-transition due to the Ps-Ps interaction is also evaluated in the mean-field approximation.
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Youhei Fujitani
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1556-1564
Published: 2001
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An expression of the total entropy production rate of a one-component polarizable fluid without an intrinsic angular momentum is derived from conservation laws in the Newtonian mechanics. A simple expression of the field energy-momentum four-tensor derived by Imai [J. Phys. Soc. Jpn.
60 (1991) 4100] saves us a lot of calculations, and allows us to define the heat flux and the internal energy consistently. Our derivation supposes neither small polarization nor small magnetization, and terms involving them come out symmetrically. Our result is naturally expressed in terms of the fields measured in the unique inertial frame where the fluid is relaxed to be at rest.
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Fujihiro Hamba
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1565-1574
Published: 2001
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The non-negativeness of the normal stress is one of the realizability conditions for the Reynolds stress. This condition is investigated to improve turbulence models. A statistical theory called the two-scale direct-interaction approximation is modified to derive a nonlinear eddy-viscosity model that satisfies realizability for arbitrary flows. In order to check its performance, the model is used to calculate a homogeneous shear flow, a channel flow and a plane impinging jet. It is shown that a reduced eddy viscosity can suppress the excessive production of the turbulent kinetic energy in a homogeneous shear flow and a plane impinging jet. The anisotropy of the Reynolds stress in homogeneous shear and channel flows is also examined with relation to the nonlinear eddy viscosity.
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Kimitaka Itoh, Heiji Sanuki, Shinichiro Toda, Masayuki Yokoyama, Sanae ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1575-1584
Published: 2001
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Transition of radial electric field is investigated in helical plasmas for the given plasma fluxes. The density and temperature gradients are simultaneously determined together with radial electric field. The electric field shows a nature of bifurcation, if an anomalous particle transport exists in addition to the neoclassical particle flux. Based on the Maxwell's construction with respect to the work-done, the critical condition for the bifurcation is obtained. The existence of bifurcation is not affected by the anomalous energy flux. The gradients are found to be subject to bifurcation at high plasma fluxes regime. The transition to a better confinement is predicted. The presence of hard transition of the gradient and electric field indicates the existence of the electric domain interface, across which the discontinuous change of gradient takes place.
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Shinsuke Irie, Yukiharu Ohsawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1585-1592
Published: 2001
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Propagation of low frequency waves along a uniform external magnetic field in a cold plasma with multiple ion species is studied theoretically and numerically. First, linear dispersion relations are calculated, and nonlinear evolution equations are derived. The right circularly polarized wave does not suffer significant change by the presence of multiple ion species. However, the left circularly polarized wave greatly changes its properties. The Alfvén and ion cyclotron waves are split into two modes in a two-ion-species plasma. These waves are unstable against modulational instability except for a small frequency domain; the growth rates are especially large near the ion cyclotron frequencies. Then, the development of the instability is further investigated with simulations based on a three-fluid model. The growth rates measured in the simulations are in good agreement with the theoretical prediction. Also, it is shown that the growth rates can be greater than cyclotron damping rates for some astrophysical plasmas.
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Yasusada Yamada, Takeshi Iwase, Masaya Watahiki, Jun-ichi Suzuki
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1593-1597
Published: 2001
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We observed small angle neutron scattering in Pr
0.7Ca
0.3MnO
3 under two different magnetic fields, H = 0 and H = 1 T, focusing our attention on the lower angle region where the SANS spectra clearly show Porod-type Q-dependence. It is found that under ZFC (zero field cooling) condition, the system at low temperatures is in the state of `two-phase coexistence' where FM (ferromagnetic metallic) microcluster with the average radius of R ∼ 17 nm are embedded on AFI (antiferromagnetic insulater) background. Upon application of magnetic field, the ferromagnetic clusters start to coalesque to form macroscopic domains with the size of order of 2 μm without changing the total volume of FM region appreciablly. These conclusions seem to provide rather clear picture for CMR effect in Pr
0.7Ca
0.3MnO
3 as viewed from macroscopic standpoints.
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Takashi Yoshida, Hiroyuki Mashiyama, Tomoyuki Mochida
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1598-1603
Published: 2001
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Single crystals of a betaine-phosphate/arsenate mixed system (30% P was replaced with As randomly) were investigated by means of X-ray diffraction. The crystal structures of room temperature and of low temperature (20 K) were determined. At room temperature, the least-squares calculation converged at the R factor 3.6% with 1038 reflections. The structure is isomorphous to pure betaine phosphate. For the low-temperature structure the R factor converged at 4.3% with 4896 reflections (3.7% with 2987 normal reflections and 9.6% with 1909 superlattice reflections). The structure analysis clarifies that the hydrogen atoms of the phosphoric acid between neighboring phosphate tetrahedra are ordered in the low temperature phase resulting the superstructure (the unit cell dimension along the a-axis is doubled). By replacing P with As up to 30% in P(As)O
4 tetrahedra, the unit cell structure is changed little; only the mean size of the tetrahedra is enlarged by 2.2%.
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Tomoya Isoshima, Kazushige Machida, Tetsuo Ohmi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1604-1610
Published: 2001
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Quantum vortices in the multi-component Bose-Einstein condensation (BEC) are investigated theoretically. It is found that three kinds of the vortex configurations are possible and their physical properties are discussed in details, including the density distribution and the spin texture. By using the Bogoliubov theory extended to the three component BEC, the collective modes for these vortices are evaluated. The local vortex stability for these vortices are examined in light of the existence of the negative eigenvalue, yielding a narrow magnetization window for the local intrinsic stable region where the multi-components work together to stabilize a vortex in a self-organized way.
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Mamoru Yamashita, Toshikuni Miyazaki
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1611-1616
Published: 2001
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The smectic layer ordering at quite thin system sandwiched by parallel walls is studied by generalizing the McMillan theory on bulk smectics. The walls work as an external field on the molecules adjacent to the walls, and every order of smectic layers is preserved finite even at high temperature because the effect of walls penetrates the whole system. The order shows crossover from a long range order to a surface sustained one near a bulk transition temperature, which is analyzed as the crossover phenomenon at the critical point of the bulk system. The present theory is applied to the phase transition between two types of smectic A phases observed at the simulated system of Gay-Berne model.
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Yuri P. Monarkha, Kimitoshi Kono
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1617-1626
Published: 2001
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We present results of theoretical studies of the high-frequency conductivity of a two-dimensional Wigner solid (WS) formed on a free surface of liquid
3He. One-phonon processes are taken into account in an exact way, including a self-consistent reconstruction of the phonon spectrum caused by the interaction with surface excitations of the Fermi liquid. Multi-phonon effects are described by means of the incoherent Gaussian approximation. It is shown that the reconstruction of the phonon spectrum can substantially affect the plasmon resonance (PR) linewidth depending on the resonant frequency. If the excitation frequency is away from the bottom spectrum of WS optical modes, or the dimple lattice is disregarded, the conductivity of the WS appears to be surprisingly very close to an AC conductivity of a nondegenerate electron gas even if temperature is much lower than the Wigner-crystal Debye temperature. When the excitation frequency approaches the bottom of the optical modes, the effective collision rate of the WS decreases substantially, which explains recent PR linewidth data.
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Toru Akiyama, Atsushi Oshiyama
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1627-1634
Published: 2001
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We report first-principles total-energy calculations which reveal microscopic structures of multivacancies in Si and their feasibility of hydrogen incorporation. We find that the hexavacancy V
6 and the decavacancy V
10 are stable, and that the multivacancies are capable of containing hydrogen atoms depending on its chemical potential. We also find that an H
2 molecule is trapped in the H-decorated multivacancy. The trapped H
2 molecule as well as the Si-H bonds exhibit peculiar vibration spectra. Recent experimental data is interpreted on the basis of the present theoretical results.
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Kazuya Saito, Hiroki Akutsu, Koichi Kikuchi, Hiroyuki Nishikawa, Isao ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1635-1641
Published: 2001
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Successive metal-insulator transitions in (DIMET)
2BF
4 were studied by chopped-light ac calorimetry and electron paramagnetic resonance (EPR) measurement. An anomaly due to the metal-insulator transitions has been clearly detected in ac calorimetry between 20 and 35 K. In contrast to other double-column salts (DMET)
2BF
4 and (DMET)
2ClO
4, successive metal-insulator transitions detected in transport properties are shown to be thermodynamic phase transitions. The EPR detected an anomaly only for the lowest transition around 12 K. The properties of the metal-insulator transitions are compared among the DIMET and DMET salts having the double-column structure. A frequency-dependent step in heat capacity was detected around 110 K. The step-like anomaly is attributed to a glass transition due to freezing of the intramolecular motion of the ethylene group in the ET moiety within a DIMET molecule.
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Masanobu Aragaki, Hirotada Hoshino, Takehiko Mori
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1642-1646
Published: 2001
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A new θ-type TMET-TTP (2-[4,5-bis(thiomethyl)-1,3-dithiol-2-ylidene]-5-(4,5-ethylenedithio-1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene) salt (TMET-TTP)
2HSO
4, which has smaller dihedral angle (116
º), and has 2:1 composition, is prepared. This salt undergoes a M-I transition at around 100 K. The ESR measurement indicates that the low-temperature insulating state of this complex is paramagnetic. Thanks to this exceptional salt, a universal phase diagram of θ-type TTP salts can be discussed similarly to θ-type ET salts. In the θ-type ET salts, the universal phase diagram holds in the uniform quarter-filled band. However, our works in the θ-type TMET-TTP salts prove that the universal phase diagram is not largely influenced by the band-filling and the position of E
F.
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Takeshi Nakanishi, Tsuneya Ando
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1647-1658
Published: 2001
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The effective Hamiltonian for two crossed nanotubes is derived in a k · p scheme and the conductance between them is calculated in the Born approximation. The conductance is found to depend strongly on the crossing angle with large maxima at commensurate stacking of lattices of two nanotubes. In a magnetic field perpendicular to both nanotubes, these two maxima exhibit a field dependence completely different to each other.
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Youichi Yanase, Kosaku Yamada
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1659-1680
Published: 2001
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The pseudogap phenomena in High-T
c cuprates are investigated on the basis of the Hubbard model which includes only the on-site repulsive interaction U. We consider the pairing scenario for the pseudogap. The pseudogap arises from the resonance scattering due to the strong superconducting fluctuations. First, the electronic state and the anti-ferromagnetic spin fluctuations are calculated by using the fluctuation exchange (FLEX) approximation. The T-matrix which is the propagator of the superconducting fluctuations is calculated by extending the Éliashberg equation. The characteristics of the superconducting fluctuations due to the pairing interaction arising from the spin fluctuations are represented in the T-matrix. The self-energy due to the superconducting fluctuations is calculated by the T-matrix approximation. The pseudogap is shown in the single particle properties and the magnetic properties. Moreover, a comprehensive explanation of the doping dependence of the pseudogap is obtained. Furthermore, we apply the theory to the electron-doped cuprates and obtain the consistent results with the recent experiments. Finally, the self-consistent calculation for the spin fluctuations, superconducting fluctuations and the single particle properties is carried out within the FLEX and the self-consistent T-matrix approximations. The relation between the superconducting fluctuations and the spin fluctuations is clarified. The calculated superconducting critical temperature T
c is remarkably reduced from the results of the mean field (FLEX) calculation. In particular, it is shown that the critical temperature decreases with decreasing doping in the under-doped region with large U.
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Kenji Takanaka
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1681-1695
Published: 2001
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Ginzburg-Landau equations valid for dirty superconducting superlattices with varying characteristic parameters are derived, using the correlation function method based on diffusion process approximation. If the magnetic field is applied normal to the superlattice planes, the order parameter has spatial dependence along the direction of the magnetic field. In such a case, we numerically calculate the temperature dependence of the slope of the magnetization curve which is expressed by the parameters κ
2(T) and γ(T). The latter parameter characterizes the spatial variation of the order parameter along the direction of the magnetic field.
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Saori Kurata, Mayumi Joichi, Kazuko Kawasaki
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1696-1704
Published: 2001
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Manganites of perovskite structure have recently attracted much attention due to the colossal magnetoresistance effect and its potential application. The mother system LaMnO
3 is a Mott insulator, and is observed to be layer-type antiferromagnetic state (A-type) by neutron-scattering experiments. We calculate the dynamical correlation function S(k,ω) by means of the two time Green's function for this compound within Hartree-Fock approximation by employing the effective Hamiltonian, which consists of the spin operator S and the pseudo spin operator T for the orbital degree of freedom. We focus our attention to spin dynamics, especially regarding the interplaying between spin and orbital degrees of freedom. The results are compared with experimental data.
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Hiroyuki Shimada, Hideya Onodera, Hiroki Yamauchi, Aya Tobo, Kenji Oho ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1705-1714
Published: 2001
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Antiferroquadrupolar (AFQ) and antiferromagnetic (AFM) transitions in Ho
1-xDy
xB
2C
2 (0 ≤ x ≤ 1.0) have been investigated on the single-crystalline samples by magnetization and specific heat measurements. As the Dy concentration increases, the both transition temperatures increases from T
Q=4.5 K and T
N=5.9 K for x=0 to T
Q=24.7 K and T
N=15.3 K for x=1. For x=0.2 and 0.3, there appears a single transition at which the AFQ and AFM transitions occur simultaneously. For 0.4 ≤ x, the two transition temperatures are reversed. The temperature dependence of specific heat is interpreted well by assuming that the entropy of R ln 3 is released through the successive transitions in HoB
2C
2, that is, the 4f ground state of Ho
3+ ion is a quasi-triplet. It is supposed that the Ho
3+ ion has a rather small quadrupolar moment compared with the Dy
3+ quadrupole.
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Masato Takeuchi, Setsuro Asano
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1715-1720
Published: 2001
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The susceptibilities χ (q) of heavy rare earth metals are calculated using the results of a linear muffin-tin orbital band structure method for the eigenvalues and eigenfunctions of each metal. The results of these calculations, including Gd, are very similar to those of yttrium. The variation of the susceptibilities with changes in the Fermi level is also investigated. The region of the Fermi surface called the “webbing” is thought to play a vital role in driving the exotic magnetic structures found in a number of the heavier rare earth metals. Our calculations don't show that the susceptibilities are very sensitive to the topology of the Fermi surface. It is argued that these results require an extension of conventional models of exchange interaction in heavy rare earth metals to include magnetic ordered band structure.
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Shin-ichiro Kobayashi, Masafumi Sera, Masahiko Hiroi, Terukazu Nishiza ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1721-1730
Published: 2001
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We have studied the specific heat, magnetoresistance and magnetization of PrB
6 which shows two successive phase ransitions at T
IC from the commensurate (C) to incommensurate (IC) magnetic phase and at T
N from the IC to paramagnetic phase and obtained the magnetic phase diagram. The suppression of T
N by the magnetic field shows the following anisotropy. Below ∼12 T, T
N‹111› <T
N‹110› <T
N‹001› and above ∼12 T, T
N‹110› <T
N‹111› <T
N‹001›. T
IC is suppressed by the magnetic field for H || ‹001› and ‹110› but T
IC‹111› is enhanced largely with increasing magnetic field up to ∼10 T. It was found that the IC phase is divided into two phases below and above ∼7 T for the magnetic field around the H || ‹111› direction. The anisotropy of T
N is explained by the different magnitude of the parallel and perpendicular magnetic susceptibility whose weights depend on the magnetic field direction. The anisotropic field dependence of T
IC at low magnetic field is explained by the different magnitude of the in-plane (H || ‹110›) and out-of-plane (H || z) perpendicular magnetic susceptibility in the C phase which originates from the coexistence with the O
xy quadrupole order. The small ordered moment and twofold easy axis in the C phase are explained by the coexistence and competition between the O
xy quadrupolar and antiferromagnetic exchange interactions in the Γ
5 triplet ground state.
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Yoshihumi Tokiwa, Kiyohiro Sugiyama, Tetuya Takeuchi, Miho Nakashima, ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1731-1743
Published: 2001
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We measured the electrical resistivity, specific heat, magnetostriction, magnetization and de Haas-van Alphen (dHvA) oscillation in UPd
3 with the hexagonal structure in order to clarify the quadrupolar and magnetic properties as well as the nature of conduction electrons. The high-field magnetization measurement at 4.2 K in magnetic fields up to about 50 T reveals two-successive metamagnetic transitions at 10.2 and 17.9 T for the field along the [0001] direction, and one transition at 27.6 T along [1120]. From the results of magnetization as well as the magnetostriction measurements at various temperatures, we determined the magnetic phase diagram. Phase boundaries are discussed on the basis of the crystalline electric field scheme of the 5f
2 configuration and the quadrupolar interaction of O
zx. Reflecting the localized 5f-electrons, the conduction electrons have small cyclotron effective masses ranging from 0.24 to 3.62 m
0, which were determined by the dHvA experiment. The dHvA data are compared to the result of band calculations based on the 5f
2-localized band model.
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Yoshihumi Tokiwa, Yoshinori Haga, Etsuji Yamamoto, Dai Aoki, Narumi Wa ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1744-1750
Published: 2001
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We succeeded in growing a high-quality single crystal of an antiferromagnet UNiGa
5 by the self-flux method, and measured the de Haas-van Alphen (dHvA) effect, together with the electrical resistivity, magnetoresistance, magnetic susceptibility and specific heat. Reflecting the peculiar tetragonal structure, the Fermi surface consists of one cylindrical and two closed ellipsoidal surfaces. The cyclotron mass is not large, ranging from 1.3 to 3.1m
0.
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Hiroaki Kusunose, Yoshio Kuramoto
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1751-1761
Published: 2001
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The origin of non-collinear magnetism under quadrupolar ordering is investigated with CeB
6 taken as a target system. The mode-mixing effect among 15 multipoles is analyzed based on the Ginzburg-Landau free energy. Then the lower magnetic transition temperature and the order parameters are derived within the mean-field approximation. In the presence of pseudo-dipole-type interactions for the next-nearest neighbors, the observed pattern of non-collinear ordering is indeed stabilized for certain set of interaction parameters. The stability of the phase III
′ in the magnetic field is also explained, which points to the importance of the next-nearest-neighbor octupole-octupole interaction. Concerning the phase IV in Ce
xLa
1-xB
6 with x∼ 0.75, a possibility of pure octupole ordering is discussed based on slight modifications of the strength of interactions.
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Mitsuhiro Kawasaki
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1762-1767
Published: 2001
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Theoretical analyses of the random energy model with only two states and its extension with a hierarchy of only two levels show that these models reproduce out-of-equilibrium phenomena observed in experiments of glassy materials; the rejuvenation effect (the chaos effect), i.e. the abrupt jump and subsequent relaxation of the out-of-phase susceptibility as if the system rejuvenates when the temperature is lowered, and the power-law relaxation of the two-time correlation function. Our results suggest that also in an assembly of small systems with relaxation times distributed broadly some of these interesting out-of-equilibrium phenomena can be observed.
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Tomoaki Yamasaki, Saurav Giri, Hiroyuki Nakamura, Masayuki Shiga
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1768-1771
Published: 2001
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Magnetic and transport properties of ferromagnetic BaVSe
3 (the Curie temperature T
C ∼eq 43 K) were investigated. The resistivity shows metallic behavior. The saturation magnetization in the ferromagnetic state is homogeneously reduced to 0.34 μ
B/f.u. in contrast to the large paramagnetic moment 1.42 μ
B/f.u.; the nearly full moment value for a local spin 1/2. NMR experiments revealed a single magnetic V site below T
C. Although the macroscopic magnetic properties of BaVSe
3 is similar to those of sulfur-deficient BaVS
3-δ, BaVSe
3 is characterized by the itinerant electron magnetism in contrast to more ionic characters of the BaVS
3 system.
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Yuji Yano, Masami Kanazawa, Takenori Fujii, Nobuo Tsuda
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1772-1776
Published: 2001
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The magnetic susceptibility χ
m was measured for Ca
1-xNa
xPd
3O
4 between 2 K and 300 K. The intrinsic part of the observed χ
m is expressed by both the Curie-Weiss and the Hasegawa-Moriya formula, and Ca
1-xNa
xPd
3O
4 (x>0.3) is a metal in which the magnetic interaction between itinerant electrons will be antiferromagnetic. When analyzed by the latter theory, the Coulomb repulsion energy at an atomic site becomes 4.9 eV to 3.3 eV depending on the carrier density. Similarity and dissimilarity with high-T
c cuprates are discussed since the oxide is not superconducting at least above 2 K.
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Masahito Mochizuki, Masatoshi Imada
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1777-1789
Published: 2001
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The properties and mechanism of the magnetic phase transition of the perovskite-type Ti oxides, which is driven by the Ti-O-Ti bond angle distortion, are studied theoretically by using the effective spin and pseudospin Hamiltonian with strong Coulomb repulsion. It is shown that the A-type antiferromagnetic (AFM(A)) to ferromagnetic (FM) phase transition occurs as the Ti-O-Ti bond angle is decreased. Through this phase transition, the orbital state changes only little whereas the spin-exchange coupling along the c-axis is expected to change from positive to negative nearly continuously and approaches zero at the phase boundary. The resultant strong two-dimensionality in the spin coupling causes rapid suppression of the critical temperature, as observed experimentally. It may induce large quantum fluctuations in this region.
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Masahiro Uchida, Hidekazu Tanaka, Mikhail I. Bartashevich, Tsuneaki Go ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 6 Pages
1790-1793
Published: 2001
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Magnetic susceptibility and the magnetization process have been measured in Ba
3Mn
2O
8 polycrystal. In this compound the magnetic manganese ion exists as Mn
5+ in a tetrahedral environment, and thus the magnetic interaction can be described by an S=1 Heisenberg model. The ground state was found to be a spin singlet with an excitation gap Δ/k
B=11.2 K . Magnetization plateaus were observed at zero and at half of the saturation magnetization. These results indicate that the present system can be represented by a coupled antiferromagnetic dimer model.
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