Results 1 - 8 of 8
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[en] The three dimensional spin-1 Ising model with crystal field interactions exhibit tri-critical behaviour. Using an expansion technique for cluster identities of spin-1 localized spin systems, we study the influence of transverse magnetic field on this behaviour. Temperature-crystal-field phase diagrams is investigated for different values of transverse field. The longitudinal and transverse magnetizations, the quadrupolar moments are calculated. General formulae, applicable to structures with arbitrary coordination number N, are given. (author). 19 refs, 5 figs
[en] We study the phase diagram and magnetic properties of a transverse spin-1 Ising model with random longitudinal crystal field interactions within an expansion technique for cluster identities of spin-1 localized spin systems. The partially ordered phases appear for a particular two valued distribution P(Di) = 1/2[δ(Di-(1+α)D)+δ(Di-(1-α)D)], and for sufficiently small transverse field Ω. The longitudinal and transverse magnetizations, the quadrupolar moments are calculated. General formulae applicable to structures with arbitrary coordination number, are given. (author). 19 refs, 3 figs
[en] The effect of the chain and the dimer anisotropies on the ground state energy and the energy gap of the spin-1/2 quasi-one-dimensional antiferromagnetic Heisenberg model is investigated using a mean field theory. The dependence of the magnetization and the effective hopping parameters on the anisotropy αxy(=Jxyperpendicular/Jxyparallel) are presented for several values of the chain anisotropy. However, such a system exhibits a transition from antiferromagnetic ordered to disordered phases for arbitrary chain anisotropy and dimer anisotropy. (author). 22 refs, 11 figs
[en] The effect of the chain and perpendicular anisotropies on the energy gap for odd number of coupled quantum spin-1/2 antiferromagnetic anisotropic Heisenberg chains is investigated using a spin wave theory. The energy gap opens above a critical anisotropic value. The known results of the isotropic case have been obtained. (author). 11 refs, 4 figs
[en] The effect of the transverse magnetic field on the phase diagrams structures of the Ising model in a random longitudinal magnetic field with a trimodal symmetric distribution is investigated within a finite cluster approximation. We find that a small magnetizations ordered phase (small ordered phase) disappears completely for a sufficiently large value of the transverse field or/and large value of the concentration of the disorder of the magnetic field. Multicritical behaviour and reentrant phenomena are discussed. The regions where the tricritical, reentrant phenomena and the small ordered phase persist are delimited as a function of the transverse field and the concentration p. Longitudinal magnetizations are also presented. (author). 33 refs, 6 figs
[en] Within the framework of effective-field theory, we investigate the effects of an interface singe-ion anisotropy on the magnetic properties in the simple cubic spin-1/2 Ising model. We find a new tricritical behaviour of the interface magnetization depending on the strength of the ferromagnetic perpendicular exchange interaction the spin between the spins at the interface and their neighbors in the next layers in the right and left sides. The magnetic behaviour of an interface coupled antiferromagnetically to the two sides is also examined. (author). 25 refs, 7 figs
[en] In this work, using the ab-initio calculations, we have investigated the phantom magnetism when the diamagnetic solids, carbon and nitrogen with d doped CdTe. We have applied in these calculations the combination between the Korringa-Kohn-Rostoker and coherent potential approximation method within the local density approximation and generalized gradient approximation (GGA). In this study, the doped compound presents a metallic behavior for both the approximations characterized by a small moment of about 0.299/0.326 and 0.249/0.266 μ for 24% of C and N, respectively. The polarization has shown a low and decreasing value from 43.73/59.56 to 0.29/2.26% for 9% and 24% of C impurity concentration, respectively. Unlike for the case of N, this parameter varies from 76.7/72.86 to 85.29/83.63% for 9% and 24% concentration, respectively. In addition, we have determined the mechanism of ferromagnetic coupling for the C- and N-doped CdTe. Furthermore, the stability of the compound is investigated by comparing the energy difference between the spin glass and ferromagnetic states. It is found that below the percolation threshold, contrary to the case of doping by N except for 20% using GGA, the C impurities lead to the most ferromagnetic stable phase. While the system changes its stability above this threshold when doped by the C impurities. Finally, we have estimated and discussed the Curie temperature using the mean field approximation.
[en] Recently, a reversible and a giant rotating magnetocaloric effect has been pointed out in the multiferroic TbMnO single crystal, opening the way for new designs of low-temperature magnetic cooling. In this paper, we report a preliminary theoretical work with the aim of enlarging our understanding on the electronic, magnetic and accordingly magnetocaloric features of the TbMnO compound. Particularly, the TbMnO magnetic anisotropy is analyzed in terms of X-ray magnetic circular dichroism (XMCD) and X-ray absorption spectroscopy (XAS) spectra.