A Green's Function Treatment of a Ferromagnetic Layered System

概要

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A ferromagnetic layered spin-S system with an anisotropic exchange interaction is studied by the RPA Green's function method and the validity of the approximation is ascertained for a nearly two-dimensional Heisenberg system. The Curie temperature T_C is given in terms of the ratio α of the interlayer exchange interaction to the intralayer one and of the exchange anisotropy η, and is shown to be raised abruptly by a slight additional XY-like exchange anisotropy for the nearly two-dimensional isotropic Heisenberg model. The zero-point spin contraction increases as the system becomes XY-like and two-dimensional. For the nearly two-dimensional Heisenberg system the magnetization behaves like M_S∝1-cT^<3/2> in the vast intermediate temperature region, which amounts to (0.19〜0.72) T_C in the case of K_2CuF_4 with α=0.00066 and the XY-like anisotropy of one percent, and the present theory is in satisfactory agreement with the experimental results.
理論物理学刊行会の論文
1976-06-25