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81.
M. Tamine 《physica status solidi b》2002,231(1):71-84
The mean bulk‐like transition temperatures are calculated as a function of the concentration c in the simple cubic Ising ferrimagnetic alloys AcB1—c which have an antiferromagnetic coupling between the A and B species. The application of the calculations to the alloy FecGd1—c is presented. An effective field theory that goes beyond the mean‐field approximation is used, yielding spin values and effective exchange interaction energies. A calculation is presented for the phase diagram, giving the Curie and the compensation temperatures as a function of the alloy concentration c for given magnetic exchange constants. Such a diagram is described as a function of the JGd–Fe, JGd–Gd, and JFe–Fe exchange integral values. A fixed set of exchange interactions in the entire concentration range 0 ≤ c ≤ 1 is defined. The numerical calculations show that there is an overall qualitative agreement between theory and experiment in this range. 相似文献
82.
In the present work ferromagnetic ordering in the Hubbard model generalized by taking into account the inter‐atomic exchange interaction and correlated hopping in a partially filled band is considered. In the mean‐field approximation the ground state energy and condition of ferromagnetic state realization are found by using the Green function technique. The obtained results indicate the important role of correlated hopping. 相似文献
83.
A mixed spin Ising system consisting of spin‐1/2 and spin‐3/2 with a random field is studied theoretically by the use of effective field theory with correlations (EFT). The phase diagrams and thermal behaviors of magnetization are investigated numerically for a square lattice (z = 4) when the random field is bimodally and trimodally distributed. The results show that tricritical points exist when the external random fields H and the values of p are not too large. Re‐entrant phenomena can be seen for appropriate ranges of p and random fields H. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
84.
We develop a formalism to solve the multicomponent Falicov–Kimball model with dynamical mean‐field theory, allowing for all possible crystal‐field couplings (including spin‐orbit coupling). We apply these techniques to solve models of the intermediate‐valence transition [as seen in YbInCu4 and EuNi2(Si1–xGex)2] in the simple limit of no crystal field or spin‐orbit coupling. We show results for the uniform spin susceptibility, the average localized electron concentration, and transport properties. We also investigate the metamagnetic transition. 相似文献
85.
Electron paramagnetic resonance study of congruent LiNbO3 single crystal weakly doped (0.1 wt%) with erbium is reported. The EPR lines originating both from the 167Er isotope with a hyperfine structure, as well as from the evenEr isotopes causing fine structure, are identified. Angular dependence of the EPR lines reveals the presence of several non‐equivalent centers. Deconvolution of the EPR line into several Lorentzian components in a plane perpendicular to the z‐axis (optical c‐axis) allowed us to show the Er3+ center with the lowest (C1) point group symmetry and estimate the values of g ‐tensor. The obtained results confirmed the model of non‐ equivalent centers of the rare‐earth ions in lithium niobate having the lowest C1 symmetry due to the presence of intrinsic defects in the near‐neighborhood of RE3+. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
86.
Zhi‐Zhong Wang Yu‐Fei Wang Bi‐Yu Tang Xiao‐Qin Zeng Wen‐Jiang Ding 《physica status solidi b》2008,245(12):2749-2755
Theoretical investigation of structure, reaction enthalpies and electronic properties of the CsMgH3, Cs2MgH4, and Cs4Mg3H10 compounds were performed using the first‐principles method within generalized gradient approximation. The obtained lattice constants and position coordinates of atoms for the systems were in good agreement with experimental results. The calculated reaction enthalpies for CsMgH3, Cs2MgH4, and Cs4Mg3H10 showed that the ternary hydrides can be synthesized thermodynamically by direct reaction between Cs and Mg in hydrogen atmosphere and by appropriate combination of binary hydrides. The energy band structure and electronic density of states revealed that all of the compounds are wide‐band‐gap insulators. The electronic DOS together with charge‐density redistribution implied the significant charge transfer leading to Cs+ ions and negatively charged [MgH6]4– complex, and the dominant ionic character with noticeable covalence between Mg and H in the [MgH6]4– anionic complexes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
87.
Shao‐Yi Wu Hua‐Ming Zhang Guang‐Duo Lu Zhi‐Hong Zhang Li‐Hua Wei 《physica status solidi b》2008,245(1):188-192
The spin Hamiltonian parameters, g factors and the hyperfine structure constants for Co4+ (3d5) and Ir4+ (5d5) in SrTiO3 are theoretically studied from the formulas of these parameters for an n d5 (n = 3 and 5) ion in a tetragonally distorted octahedron with low spin S = 1/2. According to the theoretical analyses, the impurity–ligand bond lengths R ′‖ parallel to the C4 axis are found to be larger than the host values R‖ based on the phase transition rotation angles ϕ of the [TiO6]8– octahedron by the C4 axis at 4.2 and 77 K, respectively. The elongation of the ligand octahedra in the host may be enhanced in the impurity centers by the Jahn–Teller effect of the n d5 ions. The theoretical results based on the above local structures show good agreement with the experimental data. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
88.
Qun Wei Qi‐Ming Xu Zi‐Yuan Yang Dong‐Yun Zhang Jian‐Guo Zhang 《physica status solidi b》2008,245(1):193-196
The relations between the spin‐Hamiltonian (SH) parameters and crystal structure of LiNbO3:Ni2+ crystal have been established using the SH theory. On this basis, the SH parameters of LiNbO3:Ni2+ crystal have been calculated. The calculated results are in good agreement with experimental data, and this shows that the model adopted is reasonable. Also, the contributions to SH parameters from spin triplets and spin singlets are discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
89.
The relations between the spin‐Hamiltonian (SH) parameters and crystal structure of Al2O3:Cu3+ crystal have been established using the SH theory. On the basis of this, the SH parameters of Al2O3:Cu3+ crystal have been calculated, and the problem of too many adjustable parameters in previous work has been solved. The calculated results are in good agreement with experiment data. This shows that the model we adopted is reasonable. The results show that, when a Cu3+ ion is doped into Al2O3 crystal, it does not occupy Al3+ site accurately, but moves 0.0214 nm along the C3‐axis. The contributions to SH parameters from spin triplet and spin singlet are also discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
90.
Shear Viscosity to Non-Equilibrium Entropy Density Ratio of Hot Quark-Gluon Plasma at Finite Chemical Potential 总被引：1，自引：0，他引：1 
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下载免费PDF全文 In the framework of irreversible thermodynamics, we study the transport properties of hot quark-gluon plasmas. The viscous entropy production at finite chemical potential as well as the shear viscosity to non-equilibrium entropy density ratio is investigated in weakly coupled limit by using kinetic theory. The results show that the chemical potential contributes positively to their ratio compared to the pure temperature case. The ratio exhibits two boundaries in the coupling strength in which a minimum value of 0.42 is found at αs=0.6. 相似文献