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Makiko Nonomura, Takao Ohta
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
927-930
Published: 2001
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By using the model equation for microphase separation of block copolymers, we study dynamics of morphological transitions between mesophases. A coupled set of equations for the amplitudes of the modulated structures is derived in the weak segregation regime. This theory is applied to kinetics of the transition between a lamellar structure and a hexagonal structure and the results are compared with computer simulations in two dimensions.
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Dai S. Hirashima
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
931-934
Published: 2001
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Spin exchange interaction in a bilayer Wigner crystal is calculated with a WKB approximation. It is shown that the magnetic properties of a bilayer Wigner crystal are well described by the one-dimensional antiferromagnetic Heisenberg model when the interlayer distance is significantly smaller than the average interparticle distance in each layer.
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Kazutaka Kudo, Takashi Noji, Yoji Koike
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
935-938
Published: 2001
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We have measured the temperature dependences of the magnetic susceptibility in a magnetic field of 1 T and the specific heat in magnetic fields of 0-9 T for Cu
3B
2O
6 single crystals grown by the Floating Zone method. It has been found that a three-dimensional antiferromagnetic order with the spin direction parallel to the bc plane appears at low temperatures below 10 K. The spin entropy is much smaller than the value of the free-spin entropy at temperatures immediately above 10 K and recovers to the value of the free-spin entropy at approximately 50 K. Accordingly, we conclude that the two-dimensional magnetic correlation develops with decreasing temperature at low temperatures below ∼50 K, leading to the three-dimensional antiferromagnetic phase transition at 10 K.
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Hidekazu Tanaka, Akira Oosawa, Tetsuya Kato, Hidehiro Uekusa, Yuji Oha ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
939-942
Published: 2001
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Neutron elastic scattering experiments have been performed on the spin gap system TlCuCl
3 in magnetic fields parallel to the b-axis. The magnetic Bragg peaks which indicate the field-induced Néel ordering were observed for the magnetic field higher than the gap field H
g≈ 5.5 T at Q=(h, 0, l) with odd l in the a
*-c
* plane. The spin structure in the ordered phase was determined. The temperature and field dependence of the Bragg peak intensities and the phase boundary obtained were discussed in connection with a recent theory which describes the field-induced Néel ordering as a Bose-Einstein condensation of magnons.
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Hiroaki Nakamura, Susumu Fujiwara, Tetsuya Sato
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
943-946
Published: 2001
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A strange rigid-like nature for a hexagonally packed domain of short chain molecules is discovered by molecular dynamics simulation. In spite of the non-bonded short-range interaction potential (Lennard-Jones potential) among chain molecules, the packed domain gives rise to an apparent global moment of inertia. Accordingly, as two domains encounter each other obliquely, they rotate so as to be parallel to each other, keeping their overall structures as if they were rigid bodies.
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Balvir Singh Sandhu, M. B. Saddi, B. Singh, B. S. Ghumman
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
947-953
Published: 2001
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The scattering and absorption differential cross sections for non-linear QED process such as double photon Compton scattering have been measured as a function of scattering angle θ
1, when one of the emitted photon's having energy in the range 50-100 keV is detected at θ
2=φ
2=π /2. The incident gamma photons are of 0.662 MeV in energy as produced by an 8 Ci
137Cs radioactive source and thin aluminum foils are used as scatterer. The two simultaneously emitted photons resulting from the interaction of incident photons with electron of aluminum target are detected in coincidence using two NaI(Tl) scintillation detectors and a slow-fast coincidence set-up of 30 nsec resolving time. The measured values of scattering and absorption differential cross sections agree with theory within experimental estimated error of nearly 22%.
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Tosizumi Aoki
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
954-960
Published: 2001
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The two-time spin Green's function method (SGF) accompanied with the sum rule ‹ S
j-S
j++S
j+S
j-› =1, which is peculiar to the spin operators with S=1/2, is applied to the quantum Heisenberg antiferromagnets within the Tyablikov decoupling. It is emphasized that the sum rule is a strict expressin of the kinematical interaction between spin waves. The equation determining the long-range order σ is quite similar to the Tao Yuin's one obtained using theta function operator, which never yields σ =-∞ . Unfortunately, in two dimensions, the SGF can not predict the correct value of σ at T=0. By taking the critical fluctuations into account, we attempt to dissolve this discrepancy. As a result, it is suggested that a cancellation occurs fairly well between the critical fluctations and the kinematical interaction in two dimensions.
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Yasufumi Susuki, Hiroki Nakano, Katsuhiko Katsura, Takeshi Ikeda
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
961-965
Published: 2001
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Dependence of the neutral fractions contained in the foil-transmitted 0.6 MeV H
+ ion beams on the angle of incidence (2.5-90 degree) has been measured at the beam direction, when (0.6-1) MeV H
+ ions are impinged on a poly-crystalline Al thin foil. The fraction for ions of the same exit-energy decreases slightly with the decreasing angle of incidence. The dependence on the angle of incidence is calculated with a classical model for charge-exchanges with a modification taking into account the topological effect of the exit-surface of the foil. The surface is observed by a three-dimensional-profile microscope and the parameters of the surface roughness are obtained. The observed parameters are consistent with those calculated from the surface topology assumed to obtain the neutral fractions comparable to the measured ones.
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Chandra Das, Shigeo Kida, Susumu Goto
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
966-976
Published: 2001
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The statistics of two-dimensional decaying turbulence are investigated by the use of direct numerical simulation in a periodic box. A number of cases are systematically compared in which the incompressible Navier-Stokes equation is solved on various resolutions and for various Reynolds numbers starting with random velocity fields of a prescribed energy spectrum. It is observed that the statistics are contaminated rapidly by the periodicity of the flow field which blocks the transfer of velocity fluctuations towards larger scales. At large Reynolds numbers the enstrophy spectrum decays similarly in time throughout the whole wavenumber range and the enstrophy decreases inversely proportionally to time.
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Daisuke Sugiyama, Mitsuhiro Nambu, Jun-ichi Sakai
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
977-982
Published: 2001
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Using a two-dimensional electromagnetic and relativistic particle-in-cell (PIC) code, we show that electromagnetic waves are excited with near fundamental plasma frequency and its second harmonics from relativistic electron beam instability, whose beam velocity is 0.8 c. It is also shown that electromagnetic waves with second harmonics can be emitted with a short time delay from the beam instability and the second harmonic waves are extraordinary waves (X-mode) propagating nearly perpendicular to an ambient magnetic field. By changing the beam velocity from 0.5 c to 0.8 c, we found that the second harmonics can make transition from R-mode like wave to X-mode. The emission mechanism of the second harmonics with X-mode characteristics is a new nonlinear process, in which the proton dynamics does not contribute at all, in contrast to the conventional three waves process. We discuss a possible emission mechanism for the present simulation result.
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Takeshi Unemura, Satoshi Hamaguchi, Masahiro Wakatani
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
983-987
Published: 2001
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For a stellarator (or tokamak) with a non-monotonic rotational transform, both the double-resonant and non-resonant interchange type modes become unstable, when the magnetic curvature is unfavorable in a finite region including the zero magnetic shear surface r=r
s. These modes generate convective motions and poloidal shear flows. The non-resonant mode driven convection affects the r ≅ r
s region significantly, although a decrease of central density is seen. On the other hand, the double-resonant mode driven convection affects the central region for a peaked density profile and a stair-like decrease of the central density is seen. The evolution of the density profile is also correlated with the behavior of the nonlinearly generated poloidal flow.
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Nobuaki Ohno, Tomokazu Kato
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
988-995
Published: 2001
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The frequencies of the fluctuations near the relaxed state of reversed field pinch (RFP) plasma in the presence of a stationary toroidal flow are investigated using magneto-hydrodynamical (MHD) theory in the approximation of the infinite aspect ratio and finite resistivity. We treat the fluctuations as MHD waves and derive their dispersion relations at the edge plasma. It is shown that there exists a new fluctuation mode with low frequency in the presence of a stationary toroidal flow, and that with the plasma resistivity it can be unstable. The dispersion relations of the new fluctuation mode and other MHD modes of the compressible plasma are obtained. The magnitudes of the frequencies are estimated using the parameters of TPE-RX, MST and RFX devices.
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Shosuke Karashima, Takahisa Koike, Yoji Makiuchi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
996-1001
Published: 2001
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The optimum conditions for soft x-ray laser amplification through the dynamics of Ar plasma, created by the capillary discharge Z-pinch, have been investigated. The numerical simulation of plasma dynamics was based on magnetohydrodynamic one-dimensional radiation model. The plasma behavior of the implosion-pinch phase was analyzed, taking plasma atomic processes into account. The optimum soft x-ray lasing occurs in the 3s-3p transition in Ne-like Ar plasma. Radiation emission and absorption processes of the resonance line on this plasma were calculated by means of escape probabilities. The temporal and spatial distribution of the density and temperature in plasmas, and the gain of lasing were evaluated at different initial discharge pressures ranging from 300 to 3000 mTorr.
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Dong-Seok Yang, Yong-Goo Yoo, Seong-Cho Yu
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1002-1005
Published: 2001
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The local structure has been examined by the extended X-ray absorption fine structure (EXAFS) for metastable Fe
80C
20 alloys produced by the mechanical alloying process. The order between Fe atoms in the alloys decreased continuously as the process time increased. The substantial changes of the local structure appears in about 6 hours milling time and the amorphization occurs between 6 and 12 hours milling time. The magnetization was interpreted by the variation of the local structure.
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Hisashi Okumura, Fumiko Yonezawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1006-1009
Published: 2001
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We investigate the atomic structure of supercritical fluids for five types of model potentials by molecular dynamics simulations. We find that the nearest-neighbor distance is almost constant while the coordination number decreases in proportion to density as fluids expand. These behaviors mean that the expansion type of supercritical fluids is
inhomogeneous. Our results support experimental results of fluids such as mercury, argon.
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Kenji Tsuda, Michiyoshi Tanaka, Kazuma Hirota, Yasuo Endoh
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1010-1014
Published: 2001
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The low-temperature ferromagnetic insulator (FMI) phase of La
1-xSr
xMnO
3 (x=0.11, 0.12) was investigated by convergent-beam electron diffraction (CBED) together with selected-area electron diffraction (SAED). We have revealed that the FMI phase belongs to the triclinic space group P1, and has a unit cell of ∼2a
c× 4b
c× 4c
c, where a
c, b
c, c
c are lattice parameters in the pseudocubic perovskite notation. These findings indicate that the FMI phase is neither the re-entrant phase of the high temperature phase (∼√ 2a
c× 2√ 2b
c× 2c
c) as reported by Kawano
et al. nor the polaron-ordering phase with a unit cell of (∼2a
c× 2b
c× 4c
c) as proposed by Yamada
et al.
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Hossein Eslami, Mohammad Mehdi Papari, Ali Boushehri
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1015-1018
Published: 2001
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In our previous paper we applied the Song and Mason equation of states to four quantum systems including
4He, Ne, H
2, and CH
4. Here, we have predicted the equation of state for the mixtures of aforementioned systems. The best intermolecular pair potentials were taken to evaluate the second virial coefficients. First and second quantum corrections on the classical second virial coefficients were taken into account. The calculated second virial coefficients have been employed to predict the molar density of hydrogen-methane binary mixtures up to a pressure of 1100 bar, and the excess molar volume of hydrogen-helium mixtures up to the pressures as high as 700000 bar. The agreement between our calculated values and the experimental data is quite good.
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Koh Wada, Shun-ichi Yoshida, Norihiro Ihara
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1019-1025
Published: 2001
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The time dependent cluster approximation called the path probability method (PPM) is applied to a pseudo-spin Ising Hamiltonian of the Slater-Takagi model for KH
2PO
4-type hydrogen-bonded ferroelectrics in order to calculate the homogeneous dynamical susceptibility χ(ω) above and below the ferroelectric transition temperature T
c. Above the transition temperature all the calculations are carried out analytically in the cactus approximation of the PPM. Below the transition temperature the dynamical susceptibility is also calculated accurately since the analytical solution of spontaneous polarization in the ferroelectric phase can be utilized. When the temperature is approached from both sides of the transition temperature, only one of relaxation times shows a critical slowing down and makes a main contribution to the dynamical susceptibility. The discrepancy from Slater model (ice-rule limit) is discussed in comparison with some experimental data.
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Masashi Degawa, Hiroki Minoda, Yasumasa Tanishiro, Katumichi Yagi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1026-1034
Published: 2001
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On Si(111) vicinal surfaces, step bunching is observed when the sample is annealed with a direct current (DC). It is also known that the DC direction that induces step bunching changes three times with the increase of temperature. Recently it was found that this step bunching instability takes place on Si(111) vicinal surfaces with off-angles up to 13-14
º [Jpn. J. Appl. Phys.
38 (1999) L308]. Temperature and off-angle dependence of the step instabilities are studied. Results show that the transition depends on the off-angle (mean step-step distance). It was also found that the off-angle dependence for a step-down current and a step-up current differs.
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Martin Albrecht, Jun-ichi Igarashi
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1035-1044
Published: 2001
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A local-orbital based
ab initio approach to calculate correlation effects on quasi particle energies in insulating solids is presented. The use of localized Wannier-type Hartree Fock orbitals allows to efficiently devide correlation effects into classes of strong, medium or small weight. Subsequently the strongly contributing correlations are obtained from a Green's function calculated by exact diagonalization, while the rest is taken into account by a perturbative treatment. With this method the band structure of LiH is calculated and reasonable agreement with experiment is found.
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Wataru Izumida, Osamu Sakai, Syunya Suzuki
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1045-1053
Published: 2001
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Systematic calculation of tunneling conductance through a quantum dot, which has a single localized orbital, is carried out by using the numerical renormalization group method. In strongly correlated case, two paired Coulomb oscillation peaks grow without large increase of their width as the temperature decreases. At the same time the peak positions shift to their central side. This behavior corresponds well with the recent experimental data, and then suggests that the Kondo effect takes place at low temperatures in the experiment. Theoretically the conductance in valley region between the two peaks gradually increases, and the peaks merge into a broad single peak as the temperature further decreases. This behavior has not been observed in the experiment. The estimated Kondo temperature for the valley region is still much less than the lowest temperature in the experiment.
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Xu-Guang Zheng, Chao-Nan Xu, Eiji Tanaka, Yoshitsugu Tomokiyo, Hiroshi ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1054-1063
Published: 2001
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There is a great current interest in understanding the role of charge stripes in high-T
c superconductivity. We found that static charge ordering and alignment of charge-ordered domains analogous to the charge stripes even exist in a compound as simple as cupric oxide, CuO. The behavior of the holes (charges) in charge-ordered CuO was extensively investigated by transmission electron microscopy, X-ray diffraction, charge transport, dielectric constant, magnetic susceptibility, and heat capacity measurements using clean single crystal samples. Correlation of charge, spin and lattice was clarified by these measurements. Further, we found a high temperature phase transition around 880 K below which charge ordering, enhanced lattice distortion and a possible orbital coupling due to the exchange of d
x2-y2 orbital of Cu, were shown to be developed. The present discovery suggests that charge stripe is quite possibly an inherent property of copper oxides and that CuO is a reference system for studying charge-spin-orbital correlation.
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Masamichi Sakai, Hajime Shibata, Masanori Shinohara
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1064-1074
Published: 2001
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We have performed a photoreflectance study of epitaxial n- and p-type GaAs layers having various carrier densities ranged between 3.0 × 10
14 and 5.8 × 10
17 cm
-3, in order to investigate influence of a surface on the Franz-Keldysh (FK) effect associated with the E
0 direct gap. It was found both in n- and in p-type GaAs that the observed FK oscillation periods are small by factors ranged between 1.3 and 2.1 compared to those expected from the built-in surface electric fields (ε
dc). A measurement of the surface photovoltaic energy suggests that modifying the surface Fermi energies (E
FS) is less feasible than using the E
FS values ranged between 0.7 and 0.8 eV (0.5 and 0.6 eV) for n-type(p-type) GaAs, that were studied in literature and used also in this study to estimate ε
dc's. We explain the reduction in the FK oscillation periods and its carrier density variations in terms of the crystal termination effect which gives rise to an optically inactive region beneath the crystal surface.
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Toshifumi Yagi, Kazuhiro Kuboki
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1075-1079
Published: 2001
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We study the effect of magnetic impurities in the d
x2-y2-wave superconducting (SC) state of the two dimensional t-J model. The spin-orbit and the spin-exchange interactions are examined by treating the impurity as a classical spin. The Bogoliubov de Gennes equation derived within a slave-boson mean-field approximation is solved numerically at T = 0. The spin-exchange scattering induces spin-triplet p-wave SC order parameters near the impurity, while a SC state with broken time-reversal symmetry and a spontaneous current appears in the presence of the spin-orbit interaction. When both interactions coexist, it turns out that a state which carries a spontaneous spin current occurs.
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Peng Chen, You Wei Du
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1080-1083
Published: 2001
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Large magnetic entropy change (7.5 J/kg· K) was discovered in Nd
0.5Sr
0.5MnO
3 under a low magnetic field of 10 kOe at charge-ordered state transition temperature (183 K). It exceeds the magnetic entropy change in Gd by a factor of 2.4 at phase transition temperature under same magnetic field. The physical mechanism is related to the field-induced first-order magnetic, electron and structural transition (from antiferromagnetic charge-ordered state to ferromagnetic charge-disordered state).
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Kenji Suzuki, Yasuo Yamaguchi, Takejiro Kaneko, Hajime Yoshida, Yoshih ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1084-1089
Published: 2001
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The compounds MnN and FeN were prepared as single phase sample by DC reactive sputtering. The crystal structure of MnN is tetragonally distorted NaCl type and that of FeN is ZnS type. Temperature dependence of the neutron diffraction pattern on MnN was investigated. Analysis of the data shows that the magnetic structure of MnN consists of ferromagnetically aligned c-planes coupled antiferromagnetically in the c-direction. The magnetic moment of manganese atom extrapolated to 0 K was found to be 3.3μ
B and lie in c-plane. The neutron diffraction measurements of the compound FeN were also carried out. The ZnS type FeN was concluded to be non-magnetic down to 2.2 K.
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Masaya Watahiki, Naoto Metoki, Jun-ichi Suzuki, Ken-ichi Oikawa, Jiaca ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1090-1098
Published: 2001
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In order to make clear a correlation between mesoscopic ferromagnetic cluster and the colossal magnetoresistance in perovskite based manganites, the systems (La
1-xTb
x)
2/3Ca
1/3MnO
3 with x = 0.1 and 0.3 have been studied by small-angle neutron scattering technique. We investigated the property of mesoscopic ferromagnetic (short range ordered) cluster under the various magnetic fields and temperatures. In the sample of x = 0.3, a large number of short range ordered cluster is created below T = 150 K and persists in the two-phase coexistence state down to 8 K. The short range ordered clusters merge into single ferromagnetic domains with applying magnetic field of H = 5 T, resulting in the drop of resistivity of the order of 10
4. According to our model calculation, we found that roughly 50% of the system remained short range ordered phase at T = 8 K and H = 0 T. The fractional volume of the short range order phase decreased to 18% with applying magnetic field up to H = 1 T.
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Munetaka Sasaki, Koji Nemoto
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1099-1104
Published: 2001
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Magnetizations are introduced to the Generalized Random Energy Model (GREM) and numerical simulations on ac susceptibility is made for direct comparison with experiments in glassy materials. Prominent dynamical natures of spin glasses, i.e.,
memory effect and
reinitialization, are reproduced well in the GREM. The existence of many layers causing continuous transitions is very important for the two natures. Results of experiments in other glassy materials such as polymers, supercooled glycerol and orientational glasses, which are contrast to those in spin glasses, are interpreted well by the Single-layer Random Energy Model.
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Osamu Sakai, Shunya Suzuki, Kenichi Nishizawa
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1105-1116
Published: 2001
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We developed a Monte Carlo method to study the magnetic and transport properties of low density carrier ferromagnetic (FM) semiconductors. The calculation is carried out for the two- and three-dimensional Ising spin system interacting with electrons through the s-d exchange coupling. When the temperature increases from T=0, the spontaneous magnetization of the local spins decreases appreciably in the low T range, and steeply at the Curie temperature (T
C). The initial decrease is caused by the almost complete escape of electrons from the spin flipped sites, and accumulation in the FM region. The electron spin polarization is complete in the whole FM temperature range except very near T
C. The Curie temperature shifts to low T side from the value estimated based on the RKKY model as the exchange constant increases. The critical-scattering-like peak of the resistivity appears near T
C when the exchange interaction is not so strong, but it disappears when the interaction is strong. In the former cases, the initial decrease of the magnetization is not so noticeable. The intensity of AC conductivity transfers from ω ∼ 0 range to the frequency range characterized by the excitation energy of the magnetic polaron state.
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Hiroki Fujimori, Daisuke Kuwahara, Toshihito Nakai, Seiichi Miyajima
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1117-1123
Published: 2001
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Significant transient
13C-
1H nuclear Overhauser effect (NOE) is observed in liquid crystal, and is explained by a local
13C-
1H dipole-dipole interaction and relaxation. Solomon's classical two-pulse experiment gives a significant maximum in signal intensity of 2.5 times the equilibrium magnetization, and also gives a way of estimating zero-quantum transition probability for a dipole-coupled
13C-
1H pair. The conventional inversion recovery sequence is recommended for the experimental determination of
13C spin-lattice relaxation rates. Magnetization recovery after the Hartmann-Hahn signal enhancement deviates strongly from exponential behavior. Experimental data are shown for an antiferroelectric chiral smectic liquid crystal MHPOBC.
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Shohei Takata, Shinji Wada, Ikuyo Shiozaki
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1124-1127
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We have carried out the nuclear magnetic resonance (NMR) of
51V in VOMoO
4, which contains linear chains of distorted VO
6 octahedra. The temperature dependence of the resonance shift K shows a small extremum around 100 K, that can reasonably be compared with the Bonner-Fisher-type behavior of the susceptibility χ.
51V relaxation rate T
1-1, on the other hand, has a complex temperature dependence: an exponential decrease down to ∼100 K, a near plateau between ∼100 and ∼34 K, and a monotonous decrease below ∼34 K. These are interpreted in terms of thermal-excitations between split t
2g orbitals in energy (ΔE∼680 K) due to the local distortion of VO
6 octahedra at high temperatures, one-dimensional d-spin fluctuations, and a short-range magnetic ordering at low temperatures, respectively. It is noted that the change in the a-axis length must be taken into consideration to adequately describe the broad maximum observed in both K and χ around 100 K. The
51V NMR in the related oxide (V
0.56Mo
0.44)
2O
5 was also carried out, in which the VO
6 and MoO
6 octahedra form a planer network sharing the corner oxygen atoms.
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Hisao Kobayashi, Yoshitaka Yoda, Takashi Kamimura
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1128-1132
Published: 2001
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The delay-time spectra of
57Fe nuclear resonant forward scattering in FeS which belongs to the boundary between the charge-transfer and Mott-Hubbard insulators have been observed under high pressure up to about 6 GPa at BL09XU in SPring-8. The observed beat patterns in delay-time spectra are distinguished two different types which correspond to the two different phases. We have successfully applied the maximum-entropy method to analyze the observed delay-time spectra. The frequencies of quantum beats which directly depend on the energy differences between two hyperfine splitting levels of
57Fe nuclei were extracted by this analysis and then the hyperfine interaction parameters were determined from there extracted frequencies. Since the evaluated magnetic hyperfine field at 0.1 MPa is smaller than that at 2 GPa, the Néel temperature of FeS with a troilite structure increases with pressure.
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Yoshiaki Kobayashi, Takeshi Miyashita, Makoto Ambai, Toshihiko Fukamac ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1133-1136
Published: 2001
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We have investigated if the wipeout phenomenon observed for the NQR signal of La
2-xSr
xCuO
4 in the region x∼ 1/8 at low temperatures, can also be observed in YBa
2Cu
3O
y system, and found no evidence in the 60 K plateau and higher carrier concentration regions of y. Only in the region of y<6.5, where at least part of hole carriers is localized, the reduction of Cu NQR spectra at low temperatures has been found. The inhomogeneous distribution of these localized carriers seems to cause the wipeout phenomenon. The wipeout phenomenon observed for YBa
2(Cu
0.98Zn
0.02)
3O
y in the wide region of y can also be understood by the same mechanism.
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Alexander L. Yablonskii, Egor A. Muljarov, Nikolai A. Gippius, Sergei ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1137-1144
Published: 2001
Released on J-STAGE: February 28, 2003
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The excitonic and photonic states in distributed feedback (DFB) microcavities may strongly couple to form DFB cavity polaritons, provided that excitonic oscillator strength is large enough. In this paper we theoretically analyse the optical properties of DFB microcavities related to polariton effect. A numerical method based on scattering matrix formalism has been developed to solve the Maxwell's equations for layered system with periodical patterning of layers. To incorporate polaritonic effect in our model we included the exciton poles in dielectric susceptibility of one of the patterned layers. Using this method we reproduce the characteristic features, demonstrated in recent experiments [Fujita
et al.: Phys. Rev. B
57 (1998) 12428], such as anticrossing behavior of transmission dips in vicinity of the excitonic resonance and strong polarization dependence of their position and depth.
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Kaizo Nakamura, Minoru Shigoku, Kanji Kondo, Hiroshi Nagasaki, Osamu A ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1145-1153
Published: 2001
Released on J-STAGE: February 28, 2003
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Various aspects of luminescence in β-ZnP
2 have been investigated at low temperatures. Formation of exciton molecules is confirmed under the CW resonance excitation into the lowest 1
s triplet exciton absorption band. The exciton molecule emission band M appears at a moderately weak laser power. Low energy component C
L1 of the singlet luminescence comes from the anti-Stokes acoustic phonon scattering of the triplet excitons. From the outgoing resonance of the LO Raman line, it is confirmed that the high energy component C
L2 has many strong phonon sidebands, while low energy component C
L1 has no sideband. Furthermore, a novel luminescence C
T resulted from the anti-Stokes scattering of the triplet excitons has been found. From detailed excitation spectra, we can deduce some of the relaxation paths of the exciton polaritons.
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Yasuhiro Funabashi, Kiyoshi Kawamura, Ken-ichi Oshio, Satoru Morita, Y ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1154-1161
Published: 2001
Released on J-STAGE: February 28, 2003
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For the physical study of the native responses of
Caenorhabditis elegans (
C. elegans), probability distribution of random walkers on the neuron graph is studied. Here, the neuron graph is a graph which represents the synaptic connection of neurons of the worm. Connection of a sensory neuron to various motor neurons are represented by an index named accessibility. Accessibilities from 39 sensory neurons to all of motor neurons are computed and the formers are classified into three groups. It is found that this classification coincides with the grouping by native responses caused by those sensory neurons. This coincidence implies the usefulness of the random walker model for the analysis of the neural network. The connectivity represented by the major paths of random walkers is a significant factor to interpret relation between external disturbance and resultant movement in the native response of the worm. This native response of the worm is encoded by the connectivity of vertices in the neuron graph.
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Takahisa Shobu, Yukio Noda, Kazuaki Iwasa, Abdul Hannan, Masahumi Kohg ...
Article type: General Physics
Subject area: Mathematical methods in physics.
2001 Volume 70 Issue 4 Pages
1162-1163
Published: 2001
Released on J-STAGE: February 28, 2003
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