Phase Transition of Nearly Two-Dimensional Heisenberg Ferromagnets with Weak Perturbations

概要

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The double-time Green's function method incorporated with Tyablikov's decoupling is applied to the nearly two-dimensional ferromagnets of layer-structure copper compounds. Besides the strong intralayer ferromagnetic exchange interaction we take account of weak perturbations, i.e., interlayer exchange interaction, intralayre exchange anisotropy, and dipolar interaction. We obatin the leading two in the inverse transition temperature T_c^<-1>, i.e., terms logarithmically singular and constant with respect to the weak perturbation. Spin contraction at zero temperature is very small. Outside the very vicinity of zero temperature the equation for spontaneous magnetization σ as a function of k_BT/2J is reduced to a much simpler one containing only one parameter k_BT_c^<calc>/2J. Comparison of the calulated T_c and temperature dependence of σ with experimental deta seems to show the soundness of applying the RPA theory to these systems. The contributions of dipolar interaction are examined.
社団法人日本物理学会の論文
1975-11-15