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/ S. S. Aplesnin // J. Exp. Theor. Phys. - 2000. - Vol. 90, Is. 1. - P. 194-201, DOI 10.1134/1.559075. - Cited References: 35 . - ISSN 1063-7761РУБ Physics, Multidisciplinary

Аннотация: An approximation dependence of the spontaneous magnetic moment at a site, sigma/sigma(0) - 1 = 0.71(6)delta(2.5(2)), and the antiferromagnet-singlet state phase boundary, J(2)/J(1) = 0.52(3)delta, are determined by the quantum Monte Carlo method in the self-consistent sublattice molecular field approximation for weakly interacting (J(2)) antiferromagnetic chains with spin S = 1/2 and alternating exchange interaction (J(1) +/- delta). The Neel temperature and a number of critical temperatures which could be related with the filling energy of two singlets (Delta S-z = 0) and one triplet (Delta S-z= 1) spin bands, each of which is split by the sublattice field (h(x,y)not equal h(z)) into two subbands, are determined on the basis of the computed correlation radii of the two- and four-spin correlation function, the squared total spin (S-z)(2) with respect to the longitudinal components, the dimerization parameter, and the correlation functions between the nearest neighbors with respect to longitudinal and transverse spin components. On the basis of the Monte Carlo calculations, the critical temperatures and possible energy gaps at the band center are determined for the antiferromagnets CuWO4 and Bi2CuO4 and for the singlet compounds (VO)(2)P2O7 and CuGeO3 , agreeing satisfactorily with existing results, and new effects are also predicted. (C) 2000 MAIK "Nauka / Interperiodica".

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Держатели документа:
Russian Acad Sci, Siberian Div, LV Kirensky Phys Inst, Krasnoyarsk 660036, Russia
ИФ СО РАН

Доп.точки доступа:
Аплеснин, Сергей Степанович

/ S. S. Aplesnin // J. Exp. Theor. Phys. - 1997. - Vol. 85, Is. 6. - P. 1196-1203, DOI 10.1134/1.558393. - Cited References: 33 . - ISSN 1063-7761РУБ Physics, Multidisciplinary

Аннотация: The two-dimensional Heisenberg spin-1/2 model with alternated exchange interaction along the c axis and an anisotropic distribution of the exchange interaction in the lattice, J(b)/J(c)=0.1, is examined. A quantum Monte Carlo method is used to calculate the phase diagrams of the antiferromagnet, the dimer state in a plane, the value of the alternation delta of the exchange interaction, and the anisotropy Delta=1-J(xy)/J(z) of the exchange interaction, Delta similar to delta(0.58(6)). The following characteristics are calculated for Delta=0.25: the dependence of the temperature of the dimer-state-paramagnet transition on the alternation of the exchange interaction, T-c(delta)=0.55(4(delta-0.082(6))(0.50(3)), the singlet-triplet energy gap, and the dependence of the magnetization on the external field for some values of delta. The value of the exchange interaction, J(c)=127 K, the alternation of the exchange interaction, delta=0.11J(c), and the correlation radius along the c axis, xi(c) approximate to 28c, are determined. Finally, it is found that the temperature dependence of the susceptibility and the specific heat are in good agreement with the experimental data. (C) 1997 American Institute of Physics. [S1063-7761(97)01912-4].

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Держатели документа:
Russian Acad Sci, LV Kirensky Phys Inst, Siberian Branch, Krasnoyarsk 660036, Russia
ИФ СО РАН

Доп.точки доступа:
Аплеснин, Сергей Степанович

/ S. S. Aplesnin // Fiz. Tverd. Tela. - 1996. - Vol. 38, Is. 6. - P. 1868-1877. - Cited References: 30 . - ISSN 0367-3294РУБ Physics, Condensed Matter


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