Long-range isotropic and dipolar spin-spin interactions in the square planar rotator model

被引:18
作者
Rastelli, E [1 ]
Regina, S
Tassi, A
Carbognani, A
机构
[1] Univ Parma, Dipartimento Fis, I-43100 Parma, Italy
[2] CNR, MASPEC, I-43100 Parma, Italy
[3] Ist Nazl Fis Mat, I-43100 Parma, Italy
来源
PHYSICAL REVIEW B | 2002年 / 65卷 / 09期
关键词
D O I
10.1103/PhysRevB.65.094412
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
The simultaneous presence of a long-range isotropic anti ferromagnetic interaction decaying as 1/r(3) (where r is the spin-spin distance) and of a dipolar interaction in the square planar rotator model is studied. The pure isotropic anti ferromagnetic interaction does not support long-range order, at variance with the pure dipole interaction. The model is investigated analytically at low temperature and by Monte Carlo (MC) simulations at higher temperature. The Luttinger-Tisza method provides a ground-state configuration affected by continuous degeneracy. Thermal fluctuations accounted for by the linear spin-wave approximation lift the degeneracy and lead to order by thermal disorder. Different kinds of order are found going from a pure anti ferromagnetic to a pure dipole interaction. The mechanism that restores long-range order is understood by using the renormalized spin-wave theory. The accidental soft mode related to the continuous degeneracy of the ground state is replaced by a temperature-dependent gap. Temperature-driven first-order phase transitions between different ordered phases are investigated via a Landau functional. The phase diagram of the model is obtained by study of the order parameter, specific heat, and staggered magnetization evaluated by MC simulations.
引用
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页码:1 / 16
页数:16
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