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Katsumi Hagita, Hiroshi Takano
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
673-676
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Relaxation modes and rates of a polymer chain in a melt are studied by Monte Carlo simulations of the bond fluctuation model, where only the excluded volume interaction is taken into account. Polymer chains, each of which consists of N segments, are located on an L × L × L simple cubic lattice under periodic boundary conditions, where each segment occupies 2 × 2 × 2 unit cells. The results for N=32, 48, 64, 96, 128, 192, 256, 384 and 512 at the volume fraction φ ∼eq 0.5 are reported, where L = 128 for N ≤ 256 and L=192 for N ≥ 384. The relaxation modes and rates are estimated by solving generalized eigenvalue problems for the equilibrium time correlation matrices C
i,j (t) = 1/3 ‹ R
i (t) · R
j (0) › of the coarse-grained relative positions R
i of segments of a polymer chain defined by R
i = 1/n ∑
k=1n R
(i-1)n+k, where R
k denotes the position of the kth segment relative to the center of mass of the polymer chain. The apparent exponent z which describes the N-dependence of the slowest relaxation rate λ
1 as λ
1 ∝ N
-z increases beyond three as N increases. From the data for N = 256, 384 and 512, the apparent exponent is estimated to be z ∼eq 3.5. The behavior of the pth slowest relaxation rate λ
p for a fixed value of N is consistent with the prediction of the reptation theory λ
p ∝ p
2. The first and second slowest relaxation modes show the Rouse-like behavior.
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Jiro Mizushima, Takanori Nakamura
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
677-680
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The mathematical origin of the repulsion of eigenvalues in the Rayleigh-Bénard problem in a rectangular cavity is explored by considering a partially nonslip boundary condition at the side walls. It is known that the eigenvalues, i.e., the neutral Rayleigh numbers, intersect each other at critical aspect ratios under the stress-free boundary condition at the side walls when the eigenvalues are plotted against the aspect ratio of the cavity, but repulse each other under the nonslip boundary condition. The linear eigenvalue problem for the occurrence condition of convection is solved by double expansions in the deviation of the aspect ratio from one of the critical values and the nonslip parameter. It is found that the repulsion of eigenvalues arises from a structural instability of the transform of matrices into a Jordan canonical form, and the magnitude of the gap between two eigenvalues is evaluated.
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Miwako Takahashi, Timbangen Sembiring, Masatomo Yashima, Toetsu Shishi ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
681-684
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
In situ neutron diffraction experiments were performed on single crystals of Pt-12.5 and 14.4 at.% Mn alloys in order to elucidate the ordered structures of Pt-rich Pt-Mn alloys. The observed diffraction patterns at various temperatures up to 1050
ºC have revealed two ordered phases in these alloys. Below the order-disorder transition temperature, a Cu
3Au type ordered structure appears and at low temperature, an ABC
6 type ordered structure with a unit cell 2 × 2 × 2 as large as that of the fundamental fcc cell was found to be stable. A secondary ordering in the alloys is discussed in terms of two order parameters in the ABC
6 type structure utilizing the method of static concentration waves originally proposed by Khachaturyan [Prog. Mater. Sci.
22 (1978) 24]. The ideal alloy composition for the structure is also discussed with the experimentally estimated order parameters.
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Hisashi Okumura, Fumiko Yonezawa
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
685-688
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We derive a new approximate formula for the bulk viscosity ζ in terms of microscopic information such as the interatomic potential φ(r) and the pair distribution function g(r). This is a unique characteristic of this expression when compared with the previously proposed formulae in which the bulk viscosity ζ is expressed in terms of pressure. Debye relaxation is assumed for g(r) in the derivation of this approximate formula, and it is an effective method of determining a correct order of magnitude. This is confirmed by performing simulations of a Lennard-Jones fluid near its triple point.
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Sei Suzuki, Yusuke Kato, Yoshio Kuramoto
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
689-692
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The electron-removal spectrum in a fractional quantum Hall (FQH) droplet with a Landau level filling 1/p (p: odd integer) is derived numerically. The spectrum of a small-sized droplet as a function of the removed angular momentum shows a p-fold iterative structure at the lower threshold. The structure is due to quasi-holes, and is analogous to the twice refrained spinon thresholds in the dynamical structure factor of the Heisenberg chain. It is discussed that the iterative structure should remain in the FQH droplet with a large number of electrons.
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Ryuta Watanuki, Taichi Terashima, Kazuya Suzuki
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
693-696
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Fermi surfaces of LaB
2C
2 were investigated by the measurement of the de Haas-van Alphen (dHvA) oscillations. The angular dependence of the dHvA frequency indicates the presence of the multiple three-dimensional closed Fermi surfaces, that is, the 5d orbitals in lanthanum strongly hybridize with the 2p orbitals in boron-carbon sheets. The angular dependence of the dHvA frequency coincides very well with that predicted by the band calculations. The branch having the highest frequency larger than cross-section of the 1st Brillouin zone corresponds to the large orbit originating from magnetic breakdown.
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Muneo Sugiura, Yoshikazu Suzumura
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
697-700
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The effect of correlation on Peierls transition, which is accompanied by a dimerization, t
d, of a bond alternation for transfer energy, has been examined for a half-filled one-dimensional electron system with on-site repulsive interaction (U). By applying the renormalization group method to the interaction of the bosonized Hamiltonian, the dimerization has been calculated variationally and self-consistently with a fixed electron-phonon coupling constant (λ) and it is shown that t
d takes a maximum as a function of U. The result is examined in terms of charge gap and spin gap and is compared with that of the numerical simulation by Hirsch [Phys. Rev. Lett.
51 (1983) 296]. Relevance to the spin Peierls transition in organic conductors is discussed.
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M. N. McBrien, N. E. Hussey, P. J. Meeson, S. Horii, H. Ikuta
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 71 巻 3 号 p.
701-704
発行日: 2001年
公開日: 2003/04/25
ジャーナル
認証あり
We report measurements of the resistivity ρ(T) of high-quality single crystals of PrBa
2Cu
4O
8 along all three principal axes. Substitution of Pr for Y in YBa
2Cu
4O
8 completely suppresses superconductivity through localisation of the in-plane charge carriers. At low temperatures, however, ρ(T) is found to be metallic, ρ(T) ∼ T
2 for all three crystallographic directions, and is highly one-dimensional (in-plane anisotropy ρ
a/ρ
b ∼ 1000). These results reveal that the CuO double chain network forms a highly anisotropic Fermi liquid ground state at low T. Furthermore, the observation of metallic c-axis resistivity in PrBa
2Cu
4O
8, in the absence of mobile carriers on the planes, confirms that c-axis transport in Y-based cuprates is dominated by the chain carriers.
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S. Shinomori, Y. Okimoto, M. Kawasaki, Y. Tokura
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
705-708
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Successful fabrication of epitaxial thin films of La
2-xSr
xNiO
4 (0.5≤ x ≤ 1.4) has enabled us to investigate the change in charge dynamics upon the insulator-metal transition (IMT). The charge gap induced by (π,π) charge ordering as observed in optical spectra for x=0.5 is decreased with the increase of x, while the pseudo-gap feature subsists at least up to x=1.0 beyond IMT critical point (x
c ≈ 0.9). In the metallic phase near IMT, the Hall coefficient shows remarkable enhancement at low temperatures. The results indicate the predominant role of the charge ordering/correlation in the IMT.
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Ryosuke Kadono, Wataru Higemoto, Akihiro Koda, Yu Kawasaki, Masashi Ha ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
709-712
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The quasiparticle excitations in the mixed state of Cd
2Re
2O
7 have been studied by means of muon spin rotation/relaxation (μSR). The temperature dependence of the magnetic penetration depth (λ) is consistent with a nearly isotropic superconducting order parameter, although a slight discrepancy which is dependent on the details in the analysis may be present. This is also supported by the relatively weak field dependence of λ.
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Hiroshi Shimahara
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
713-716
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We propose a mechanism by which the paramagnetic pair-breaking effect is largely reduced in superconductors with coexisting antiferromagnetic long-range and short-range orders. The mechanism is an extension of the Jaccarino and Peter mechanism to antiferromagnetic conductors, but the resultant phase diagram is quite different. In order to illustrate the mechanism, we examine a model which consists of mobile electrons and antiferromagnetically correlated localized spins with Kondo coupling between them. It is found that for weak Kondo coupling, the superconductivity occurs over an extraordinarily wide region of the magnetic field including zero field. The critical field exceeds the Chandrasekhar and Clogston limit, but there is no lower limit in contrast to the Jaccarino and Peter mechanism. On the other hand, for strong Kondo coupling, both the low-field superconductivity and a field-induced superconductivity occur. Possibilities in hybrid ruthenate cuprate superconductors and some organic superconductors are discussed.
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Yoshiro Shimojo, Takehiko Ishiguro, Takashi Toita, Jun-ichi Yamada
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
717-720
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The superconductivity (SC) of a layered organic salt β-(BDA-TTP)
2SbF
6 with a new donor molecule centered with tetrathiapentalene (TTP) has been characterized by the temperature dependence of the upper critical field H
c2(T) and the specific heat. The SC transition behaviors observed via the resistive and magnetic susceptibility measurements are different at finite temperatures, probably due to the influence of vortex dynamics. The SC parameters including the coherence lengths are evaluated based on the H
c2(0)'s in the magnetic fields applied parallel and perpendicular to the SC plane, in combination with the specific heat data.
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Masako Saito, Masao Ogata
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
721-724
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We investigate effects of a single impurity on the spin-Peierls system using a simplified one-dimensional XY model coupled with lattice distortion in terms of fermions representing spin operators in the continuum limit. An impurity is assumed to reduce the spin-lattice coupling around it. It is shown that midgap bound states appear around the impurity and consequently the lattice distortion is reduced there. Magnetization can be induced there under adequate boundary conditions. The results are compared with the recent results by a phase Hamiltonian.
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Yoshihumi Tokiwa, Yoshinori Haga, Naoto Metoki, Yoshinobu Ishii, Yoshi ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
725-728
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The crystal and magnetic structures of 5f itinerant antiferromagnets UNiGa
5 and UPtGa
5 were studied by means of neutron scattering. The powder diffraction data were well explained by the HoCoGa
5 tetragonal structure with space group P4/mmm. In UNiGa
5, uranium spins in the simple tetragonal lattice have a Néel-type structure with a relatively large moment of 0.9 μ
B/U along the [0,0,1] direction. On the other hand, magnetic moments of uranium atoms in UPtGa
5 are aligned ferromagnetically in the (0,0,1) plane and are directed along the [0,0,1] direction in an antiferromagnetic sequence (↑↓). An ordered moment is 0.24 μ
B/U. The nearest-neighbor interaction might be different in these isostructural compounds.
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Kazuyoshi Takeda, Masaki Mito
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
729-731
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
At high pressures exceeding 9 GPa, the disappearance of the ferromagnetism of iron has been detected by magnetization measurements. The value of this critical pressure is consistent with the theories in which the Stoner condition for ferromagnetism has been examined along with the martensitic transition path from the bcc to the hcp structure of iron. The sluggish or hysteresis behavior of the compressed iron is discussed.
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Satoshi Endo, Takayuki Goto, Tetsuo Fukase, Hiroshi Matsui, Hiroshi Uo ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
732-734
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
For an organic π-d metal λ-(BEDT-TSF)
2FeCl
4, where BEDT-TSF is an abbreviation of bis(ethylenedithio)tetraselenafulvalene, we have measured
1H-NMR to clarify the quite anomalous ferroelectric-like metallic states below T
FM = 70 K recently found in the microwave conductivity and specific heat measurements as well as the metal-to-insulator transition at T
MI = 8.3 K associated with antiferromagnetic ordering. Just at the temperature T
FM, the second-order ferroelectric-like phase transition temperature, a single peak at higher temperatures of 100 K and 80 K starts to split into three asymmetric peaks, which are analyzed by Gaussian deconvolution with three components. It is considered that this anomalous splitting of the NMR spectra is attributed to the hyperfine field between the proton nucleus and π electrons. This anomaly at T
FM is discussed in terms of a charge disproportionation.
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Mariko Higuchi, Takashi Odagaki
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
735-738
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Combining the intermediate scattering function of the center of mass and that of individual atoms obtained by molecular dynamics simulation, we devise a method of analyzing the contribution of the internal motion in the relaxation process. We apply the analysis to the relaxation process of a model diatomic molecular system in the supercooled state and show that the rotational motion gives rise to the slow relaxation compatible with the Johari-Goldstein process.
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Ryuji Ishizaki, Hiroyuki Shiraishi, Masato Kanie, Masayoshi Inoue
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
739-743
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The dynamics of a decimal point of two-sided infinite sequences (… a
t(-2) a
t(-1). a
t(0) a
t(1) …) is studied, where the motion of the point is governed by a generalized shift (GS) map. Diffusive motion and fluctuated drift motion are observed which depend on the rule of GS. We introduce a parameter P which is the probability of a
(i+1)0 whose value is the same with a
(i)0. We calculate the mean square displacement σ
2(n) ∝ n
ζ for a fluctuated drift rule, and find that super-diffusive (ζ∼eq 1.96) and sub-diffusive (ζ∼eq 0.93) for P=0.5. Pathological anomalous diffusion (ζ > 2) is observed if P approaches to 1.
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Shouzou Sugitani, Kuniaki Nagayama
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
744-756
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
A comparative approach to investigate what is renovated in transmission electron microscopy (TEM) with the recently proposed complex observation is reported. To make the comparison quantitative among various TEM schemes proposed to date, a novel TEM index, information transfer reliability (ITR), was introduced based on a linear inverse theory originally developed to characterize measurement models. ITRs regarding to four different observation schemes (two unreplaceable schemes: bright-field (conventional) and Zernike phase-contrast, and two derived schemes: defocus series based on conventional and complex obtained from a combination of conventional and Zernike phase-contrast) were calculated for the images respectively obtained with computer simulation for a protein, a high potential sulfur protein. Recognition of the 0.5 nm-diameter prosthetic group, an iron-sulfur cluster, included in the protein was used as a criterion for good-quality images. Based on the argument on the relation between the recognizability by our image perception and the TEM index ITR calculated for the same image, superiority in the observation scheme was quantitatively confirmed for the complex observation and its single experimental version, phase-contrast.
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K. S. Grabowski, G. K. Hubler, D. L. Knies, R. A. Walker, S. B. Qadri, ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
757-761
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
TiH
2 and TiD
2 thick targets were bombarded with 100 to 200 keV protons. Evidence for nuclear reactions was obtained by means of a surface barrier particle detector. Proton irradiation of TiD
2 produced the following observations: α particle emission identified as (p,α) reactions from
11B and
7Li impurities in the target at ppm concentrations; and ∼3 MeV proton and ∼1 MeV triton emission from secondary D-D reactions caused by elastic scattering of the primary proton with a target deuteron. A 3.9 MeV α particle peak measured by others was not observed.
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Jingwen Xu, Lianjun Liu, Youdong Mao, Beiwen Li
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
762-766
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The purpose of this paper is to present a new general approach to solve ground-state energies of the double-electron systems in a uniform magnetic field, in which the basic element of evolution is the set in the solution space, rather than the point. The paper defines the Cell Evolutionary Algorithm, which implements such a view of the evolution mechanism. After we get the optimal set in which the optimal solution may be, then this approach applies the embedded search method to obtain the optimal solution. We tested this approach on atomic structure, and results show that it can improve not only the efficiency but also the accuracy of the calculations as they relate to this specific problem.
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Yasushi Nomura, Tai-ichi Shibuya
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
767-772
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Characteristics of linear and third-order optical responses are investigated for a system consisting of identical oscillators coupled dendrimerically with each other. Each oscillator is assumed to be harmonic and optically excitable. Dependences of these responses on the size of the dendrimeric system are examined with numerical calculations on the oscillator strength and the third-order polarizability. It is shown that the total oscillator strength increases linearly with the number of the oscillators, whereas the third-order polarizability increases far more steeply. From the microscopic viewpoint, there are two types of processes that contribute to the third-order polarization of a molecular aggregate system: One type is the induction of the third-order polarization at each molecular unit, and the other is the cooperative participation of the units. Contributions of these processes to the total polarization are examined. It is then shown that the relative importance of the latter type increases as the size of the dendrimeric system gets large.
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Seiji Tsurubuchi, Raita Wada, Tomoaki Nimura
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
773-776
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
A secondary electron yield from a polycrystalline Al surface was measured under Ar
+ bombardment. The yield of negatively charged particles γ(θ) was measured as a function of steady state oxygen coverage θ of target surfaces during Ar
+ bombardment. Projectile energy was changed from 20 to 80 keV. The absolute value of effective oxygen coverage θ of a target surface was determined
in situ by means of an optical spectroscopic technique in which light intensities emitted by sputtered excited atoms from the target was measured as a function of current densities of the projectile. Absolute yield of secondary electrons at zero oxygen coverage, γ(0), was obtained by measuring yield variation as a function of θ.
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Yosuke Yamazaki, Takashi Ishihara, Yukio Kaneda
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
777-781
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The effects of wavenumber truncation on the direct numerical simulation (DNS) of incompressible turbulence at high Reynolds numbers using the Fourier spectral method were studied by comparing DNS fields with different truncation wavenumbers, K
max. The comparison suggests that the error due to truncation increases faster at higher wavenumbers, k, and the increase obeys a simple scaling law in the inertial subrange k « K
max. Some statistics, such as the energy and dissipation spectra, may remain insensitive to the error, even in the later period, provided that K
maxη ∼ 1 (η is the Kolmogorov length scale), although DNS fields with different K
max are then essentially uncorrelated to each other.
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Masaaki Isobe, Koji Kimoto, Eiji Takayama-Muromachi
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
782-789
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The crystal structure of Ca
xCuO
2 (x=0.8240) has been studied by the Rietveld refinement of X-ray diffraction data using a modulated-structure analysis technique. Hole distribution was determined by bond-valence sum calculation using the obtained Cu-O inter-atomic distances. The results revealed that every third Cu site along a chain tends to be occupied by a hole. Furthermore, it was found that the Cu-O-Cu bond-angles for hole-unoccupied Cu sites are smaller than 90°. This suggests that the nearest-neighbor magnetic interaction J
1 is ferromagnetic and its magnitude is comparable to the next nearest-neighbor antiferromagnetic interaction J
2. Based on the obtained hole distribution and the signs of the magnetic interactions between spins, we proposed a possible spin/hole arrangement model in the chain, which includes a main sequence of …↑\bigcirc↓↓\bigcirc↑… in most parts of the chain.
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Takashi Mochiku, Yasumasa Mihara, Yoshiaki Hata, Shiho Kamisawa, Masaf ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
790-796
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The FeSr
2YCu
2O
6+δ compound with a Ba
2YCu
3O
6+δ-type structure exhibits superconductivity around 50 K, only when it is properly annealed in N
2 atmosphere and subsequently in O
2 atmosphere. The compound without N
2-annealing, however, does not exhibit superconductivity. This compound consists of a sequence of alternating CuO
2 double sheets with nanometer-scale separation as those in high-T
c superconductors, and FeO
δ sheets similar to that in the SrFeO
3-δ magnetic compound. Neutron diffraction study shows that both N
2-annealing and subsequent O
2-annealing cause ordering of Cu and Fe, and that both O
2-annealing and subsequent oxidization under high-O
2 pressure supply the charge. However, the charge was distributed not only to the CuO
2 sheet but also the FeO
δ sheet. The bond valence sum calculation indicates that charges distributed to the FeO
δ sheet more than to the CuO
2 sheet in the superconducting sample.
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Souichirou Tanimori, Shuji Shimamura
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
797-801
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The Monte Carlo method has been applied to the study on the size dependence of mechanical properties in gold nanocontacts. Using the Metropolis method, thermal-equilibrium atomic configurations in model nanocontacts have been followed during elongation of the contacts. The Morse potential has been used as an interatomic interaction. The relation between the tensile force and strain, the change in atomic configuration during elongation, Young's modulus and the yield stress have been investigated for three different-sized nanocontacts. The simulations show that Young's modulus and the yield stress increase as the contact size increases. While the Young's modulus tends to increase gradually to the bulk value with increasing contact size, the yield stress is expected to turn decreasing with increasing size above a certain size.
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Seiji Shibahara, Jun Yamamoto, Yoichi Takanishi, Ken Ishikawa, Hideo T ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
802-807
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We have studied the layer compression modulus B for smectic liquid crystals near the SmA-SmC
*, SmA-SmC
A*, SmA-ferrielectric phase transitions. B shows a significant pretransitional softening due to the order parameter fluctuations above the phase transitions, suggesting that these phase transitions are not of the Landau mean-field type. We also measured B near the nematic-SmA and SmA-CryB phase transitions. In the vicinity of the nematic-SmA phase transition, critical exponent of B is in very good agreement with that determined by light scattering. At the SmA-CryB phase transition, B suddenly increases without pretransitional behavior.
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Yoshiyuki Saito, Yoshihiro Suwa, Kazumi Ochi, Takahiro Aoki, Kanako Go ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
808-812
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The asymptotic behavior of the minor element, Z, in a X-Y-Z ternary alloy associated with decomposition of the major element, Y, is classified into three groups according to the sign of the second derivative of the chemical free energy f
1 with respect to the concentration of Y, c
Y and the concentration of Z, c
Z: In the case of ∂
2f
1/∂ c
Y ∂ c
Z>0, the value of c
Z along the trajectory of the peak top of the Y decreases with time. When ∂
2f
1/∂ c
Z ∂ c
Y<0 at 0≤ t<∞, peaks of c
Z formed at peak tops of Y. The amplitudes of these peaks increase with time. If ∂
2f
1/∂ c
Y ∂ c
Z<0 at 0≤ t<t
0 and ∂
2f
1/∂ c
Y ∂ c
Z>0 at t
0<t<∞, bifurcation of peaks occurs at the later stage.
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Shin-ichiro Ogawa, Makoto Tsubota, Yuji Hattori
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
813-821
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We study numerically the reconnection of quantized vortices and the concurrent acoustic emission by the analysis of the Gross-Pitaevskii equation. Two quantized vortices reconnect following the process similar to classical vortices; they approach, twist themselves locally so that they become anti-parallel at the closest place, reconnect and leave separately. The investigation of the motion of the singular lines where the amplitude of the wave function vanishes in the vortex cores confirms that they follow the above scenario by reconnecting at a point. This reconnection is not contradictory to the Kelvin's circulation theorem, because the potential of the superflow field becomes undefined at the reconnection point. When the locally anti-parallel part of the vortices becomes closer than the healing length, it moves with the velocity comparable to the sound velocity, emits the sound waves and leads to the pair annihilation or reconnection; this phenomena is concerned with the Cherenkov resonance. The vortices are broken up to smaller vortex loops through a series of reconnection, eventually disappearing with the acoustic emission. This may correspond to the final stage of the vortex cascade process proposed by Feynman. The change in energy components, such as the quantum, the compressible and incompressible kinetic energy is analyzed for each dynamics. The propagation of the sound waves not only appears in the profile of the amplitude of the wave function but also affects the field of its phase, transforming the quantum energy due to the vortex cores to the kinetic energy of the phase field.
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Kozo Okazaki, Atsushi Fujimori, Masashige Onoda
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
822-825
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We have studied the temperature-dependent electronic structure of VO
2 in the insulating phase. The V 3d and O 2p bands become broader and their band edges are shifted toward the Fermi level (E
F) with increasing temperature. The V 2p and O 1s core-level spectra also show a similar temperature dependence. These observations combined with optical spectra indicate that the position of E
F relative to the conduction-band minimum is fixed and that the band gap changes mainly below E
F. We also point out the possibility that electron-phonon interaction plays an important role in the temperature dependence of spectra in the insulating phase and may drive the metal-insulator transition.
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Takehiko Mori, Mao Katsuhara
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
826-844
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Magnetic interactions in organic conductors including magnetic anions, such as λ-(BETS)
2FeCl
4 and κ-(BETS)
2FeX
4 [X = Cl and Br], are estimated from intermolecular overlap integrals; the overlaps between anions afford J
dd, and those between anions and donors give J
π d. From this, the most stable spin alignments are decided, and such quantities as the Néel and Weiss temperatures, as well as the magnitude of spin polarization on the π-molecules are evaluated on the basis of the mean-field theory of πd-systems. The calculation is extended to several other πd-conductors, which are classified depending on the relative magnitudes of the direct dd- and indirect πd-interactions.
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Yoshihumi Tokiwa, Shugo Ikeda, Yoshinori Haga, Tomoyuki Okubo, Tomoya ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
845-851
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We succeeded in growing a high-quality single crystal of an antiferromagnet UPtGa
5 by the self-flux method, and measured the magnetic susceptibility, electrical resistivity, specific heat and de Haas-van Alphen (dHvA) oscillation. We found an antiferromagnetic transition at 26 K from the magnetic susceptibility and electrical resistivity measurements. Six dHvA branches were observed, ranging from 1.14 × 10
7 to 1.13 × 10
8 Oe. Fermi surfaces consist of two nearly cylindrical and two spherical Fermi surfaces. The cyclotron mass is large, ranging from 10 to 24 m
0, which is consistent with the electronic specific heat coefficient γ=57 mJ/K
2·mol.
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Shinya Wakoh, Maki Tokii
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
852-859
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
A linear tetrahedron method is introduced to calculate directional Compton profiles of valence electrons for cubic crystals. For the two dimensional integration a linear interpolation of both the energy and momentum density is used within each tetrahedron. They cover one 48th of the BZ (Brillouin zone) of each reciprocal vector. The program is linked to the output of FLAPW (full potential linearized augmented-plane-wave) method coded in WIEN97. As an example results for Al are described.
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Kyu Ueno, Mikio Eto, Kiyoshi Kawamura
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
860-866
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The conductance through an atomic-size point contact is examined using tight-binding models. In a case of single s band, we observe the conductance quantization in units of 2e
2/h when the atomic structure changes gradually from leads to the point contact. In the presence of broad s and narrow s bands, the conductance still seems quantized. In the presence of s and p bands, however, the conductance is substantially suppressed by the interband scattering. This is because the hybridization between s and p orbitals in the electronic states around the point contact differs from that in the bulk Bloch states, which disturbs the adiabatic conduction through the point contact. Based on the calculated results, we discuss a possible mechanism for the quantized conductance in units of e
2/h which has been observed experimentally with Ni break-junctions.
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Kazumasa Miyake, Osamu Narikiyo
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
867-871
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
It is shown on the basis of the lowest order perturbation expansion with respect to critical fluctuations that the critical fluctuations give rise to an enhancement of the potential scattering of non-magnetic impurities. This qualitatively accounts for the enhancement of the resistivity due to impurities which has been observed in variety of systems near the quantum critical point, while the higher order processes happen to give much larger enhancement as seen from the Ward identity arguments. The cases with dynamical critical exponent z=2 and z=3 are discussed explicitly.
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Mamoru Sakaue, Toshiaki Munakata, Hideaki Kasai, Ayao Okiji
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
872-879
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Electron dynamics in image states of metals are investigated by taking notice of the effects of virtual electron transitions between different image states, which are represented by off-diagonal elements of self-energy functions. Analytical formulae of both the diagonal and off-diagonal elements of the Green functions, which represent the electron densities of the image states and the probability of electron propagation between the image states, respectively, are obtained from Dyson's equations. The virtual electron transitions cause energy repulsion between the image states, and hence the decay of the electron densities can be accelerated or decelerated as compared with the decay rates given by the imaginary parts of the self-energies of the image states. Moreover, the virtual electron transitions can account for quantum beats exhibited in both the diagonal and off-diagonal elements of the Green functions. By numerical analysis, we show how the above effects are enhanced as the lifetimes of the image states become shorter.
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Kentaro Oka, Tamio Oguchi
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
880-887
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
A coadsorbed system of Li and Mg on a Cu(001) surface is studied by means of first-principles total-energy calculations within the local density approximation. It is proved that a hybrid phase in which Mg atoms are located at substitutional sites by kicking out Cu row along the [010] direction and Li atoms occupy hollow sites is the most stable geometry in the coadsorption system. Mechanism of structural stability of this coadsorption surface is discussed by comparing optimized structure, adsorption energies and electron density distribution between related coadsorbed and adsorbed surface systems.
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Takanobu Jujo
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
888-904
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The way how the magnetic field penetration depth (λ) is renormalized by the electron-electron correlation, mainly focused on high-T
c cuprates, is presented. The formula for the current carried by quasiparticle (which plays an essential role on λ
-2 and other transport phenomena) with the Umklapp scattering is derived. By relating the role of the Umklapp scattering with the irreducible four point vertex, how the value of λ
-2 deviates from that of n/m
* (n and m
* are the carrier density and the effective mass, respectively) is investigated. It is analytically shown that this deviation is small in the case where the momentum dependence of the vertex is weak, and is large and negative in the case of the strong antiferromagnetic spin fluctuation. In the latter case it is also derived that the backflow generally takes the opposite sign to the velocity with non-negligible magnitude. The observed doping dependence of λ
-2 in high-T
c cuprates, a peak structure at the slightly overdoped region, is explained by the above analytical consideration and the numerical calculation based on the perturbation theory and the spin fluctuation theory. The consistency between λ
-2 and dλ
-2/dT at absolute zero, which is the problem the isotropic model fails to explain, is also obtained by our theory.
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Yasuhiro Asano
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
905-909
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
A relation between amplitudes of Josephson current and nodes in excitation-gap of unconventional superconductors is studied in superconductor/dirty normal metal/superconductor junctions. It is found that ensemble average of the Josephson current vanishes when the junction interface is perpendicular to a plane which includes line- or point-zeros of the excitation-gap. A zero-energy state formed at the junction interface is a character of unconventional superconductor junctions and causes large sample-to-sample fluctuations in the Josephson current in low temperatures. The disappearance of the ensemble-averaged Josephson current and the large fluctuations occur at the same time when the Cooper pairs have d- or f-wave pairing symmetries.
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Kenji Kurahashi, Hiroki Matsushita, Masaki Fujita, Kazuyoshi Yamada
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
910-915
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We performed systematic post-growth heat treatments on sizable single crystals of Nd
1.85Ce
0.15CuO
4. The superconducting transition temperature, T
c, and its distribution in the sample are both sensitive to details of the heat treatment and sample size. With refinement of the heat treatment conditions we have succeeded in preparing two distinct superconducting samples in which T
c equals 18 K and 25 K under identical Ce-concentrations. Neutron scattering experiments initially observed nonmagnetic superstructure peaks at (π,π) only in the reduced superconducting phase. Atomic displacement in this structure is different from that induced by in-plane rotation of CuO
4 squares as previously reported for Gd
2-xCe
xCuO
4. A possible relationship between atomic displacements and superconductivity and the role of reduced heat treatments are discussed from the viewpoint of carrier localization.
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Isao Kagomiya, Kay Kohn, Makoto Toki, Yoshiaki Hata, Eiji Kita
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
916-921
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Dielectric constant and magnetic susceptibility have been measured on a single crystal of ZnCr
2O
4, which is a typical example of magnetically frustrated systems. Two characteristic features are observed in the temperature dependence of dielectric constant. The first is a jump of dielectric constant at the Néel temperature, where an antiferromagnetic transition presumably of the first order occurs. The other feature is dielectric dispersion appearing below 70 K, where the presence of antiferromagnetic short-range order have been demonstrated by a neutron diffraction and a temperature dependence of magnetic susceptibility. The jump indicates the presence of the lattice distortion to relax the spin frustration which otherwise prevents magnetic long-range ordering. The origin of the dispersion is presumably related to the fluctuation of interfacial charge accompanied by magnetic fluctuation.
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Kenji Kamishima, Tsuneaki Goto, Tatsuji Sasaki, Takeshi Kanomata, Tosh ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
922-926
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We have measured the magnetization of Mn
3Ga
1-xAl
xC with x=0, 0.01 and 0.02 under pressure up to 1.25 GPa. A magnetic transition from an antiferromagnetic (AFM) to an intermediate (IM) state with spontaneous magnetization is observed under pressure. We have determined the phase diagram in the pressure-temperature plane. The application of pressure increases the magnetization in the ferromagnetic (FM) phase for all these compounds. We have also measured the thermal expansion of Mn
3Ga
0.97Al
0.03C. It is consistent with the pressure effects on the magnetization and suggests the magnetic contribution to the thermal expansion as ω
mFM < ω
mIM < ω
mAFM. Neutron diffraction experiments were performed on Mn
3Ga
0.95Al
0.05C. Bragg peaks corresponding to an antiferromagnetic component were observed in the IM state. It is highly possible that the IM state has a canted ferromagnetic structure.
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A. N. Ulyanov, I. S. Maksimov, E. B. Nyeanchi, Seong-Cho Yu, Yu. V. Me ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
927-929
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The effect of lattice structure on the magnetic and transport properties of La
0.7Ca
0.3-xSr
xMnO
3 (x= 0; 0.03; 0.06; …; 0.3) lanthanum manganites have been studied. Curie temperature pressure coefficient, dT
c/dP, showed the dependence on x value. Temperature T
c increased almost linearly under applied pressure as dT
c/dP≈14 K/GPa and as dT
c/dP≈7.5 K/GPa in the orthorhombic (Pbnm) and rhombohedral (R3c) phases, respectively. The value of dT
c/dP(≈3.5 K/GPa) showed a minimum and a temperature of the resistance maximum, T
p(x), showed a change of slope at x=0.15, corresponding to the concentration structural phase transition. Differences between the values of dT
c/dP and slopes of T
p versus x in Pbnm and R3c phases are explained by the different effect of external pressure on the Mn-O bond length and Mn-O-Mn bond angle, and by the different internal pressure effect in those phases, respectively.
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Mitsuru Toda, Takao Goto, Meiro Chiba, Naoshi Suzuki
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
930-942
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The temperature dependences of spin-lattice relaxation time T
1 of
133Cs in CsFeCl
3 and
87Rb in RbFeCl
3 were measured in the temperature range between 1.5 K and 22 K, at various fields up to 7 T applied parallel (or perpendicular) to the c-axis, and the analysis was made on the basis of the dynamical correlated-effective-field approximation. The mechanism of the nuclear magnetic relaxation is interpreted in terms of the magnetic fluctuations which are characterized by the singlet ground state system. In the field region where the phase transition occurs, T
1-1 exhibited the tendency of divergence near T
N, and this feature was ascribed to the transverse spin fluctuation associated with the mode softening at the K-point. It was found that the damping constant of the soft mode is remarkably affected by the occurrence of the magnetic ordering at lower temperature, and increases largely in the field region where the phase transition occurs.
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Mikito Koga, Masashige Matsumoto
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
943-947
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The Kondo effect in a p
x + i p
y-wave superconductor is studied by applying the Wilson's numerical renormalization group method. In this type of superconductor with a full energy gap like a s-wave one, the ground state is always a spin doublet, while a local spin is shrunk by the Kondo effect. The calculated magnetic susceptibility indicates that the spin of the ground state is generated by the orbital effect of the p
x + i p
y-wave Cooper pairs. The effect of spin polarization of the triplet superconductor is also discussed.
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Shun-ichi Yoshida, Koji Nemoto, Koh Wada
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
948-954
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The cactus approximation in the cluster variation method is applied to the spin ice system with nearest neighbor ferromagnetic coupling. The temperature dependences of the entropy and the specific heat show qualitatively good agreement with those observed by Monte Carlo simulations and experiments, and the Pauling value is reproduced for the residual entropy. The analytic expression of the q-dependent magnetic susceptibility is obtained, from which the absence of magnetic phase transition is confirmed. The neutron scattering pattern is also evaluated and found to be consistent with that obtained from Monte Carlo simulations.
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Masakazu Kunitomo, Rina Etoh, Tomoyuki Hayashi, Toshiro Kohmoto, Yukio ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
955-959
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Proton spin lattice relaxation time was measured and proton NMR spectrum was observed in a purely molecular ferroelectrics, trichloroacetamide (TCAA). From the temperature and the frequency dependences of the spin lattice relaxation time, it was found that the proton spin lattice relaxation is governed by the fluctuation of proton-proton dipolar interaction in the temperature range including the phase transition temperature. From the computer simulation analysis of NMR spectra, a slight change in proton-proton distance was deduced between the ferroelectric and the paraelectric phases. The relaxation time and then the correlation time of the protonic motion change abruptly at the transition temperature. It was determined that the activation energies of the protonic motion are 1.12×10
4 J/mol and 0.80×10
4 J/mol in the ferroelectric and the paraelectric phases, respectively.
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Yoshiaki Uesu, Masaaki Matsuda, Yasusada Yamada, Kouji Fujishiro, Dave ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
960-965
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The symmetry was examined using neutron diffraction method on Pb(Zn
1/3Nb
2/3)O
3-9%PbTiO
3 (PZN/9PT) which has a composition at the morphotropic phase boundary between Pb(Zn
1/3Nb
2/3)O
3 and PbTiO
3. The results were compared with those of other specimens with same composition but with different prehistory. The equilibrium state of all examined specimens is not the mixture of rhombohedral and tetragonal phases of the end members but exists in a new polarization rotation line Mc# (orthorhombic-monoclinic line). Among examined specimens, one exhibited tetragonal symmetry at room temperature but recovered monoclinic phase after a cooling and heating cycle.
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Yasusada Yamada, Yoshiaki Uesu, Masaaki Matsuda, Kouji Fujishiro, Dave ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 3 号 p.
966-970
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The structural characteristics of the perovskite-based ferroelectric Pb(Zn
1/3Nb
2/3)
1-xTi
xO
3 at the morphotropic phase boundary (MPB) region (x∼eq 0.09) have been analyzed. The analysis is based on the symmetry adapted free energy functions under the assumption that the total polarization and the unit cell volume are conserved during the transformations between various morphotropic phases. Overall features of the relationships between the observed lattice constants at various conditions have been consistently explained. The origin of the anomalous physical properties at MPB is discussed.
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