Surface and thin film magnetization of isotropic and anisotropic heisenberg Ferromagnet at low temperatures

摘要

The independent random walk-method(which is equivalent to the nonin- teracting spin wave method) with no further approximations was used to cal- culate the low temperature expansion of: (i) the local mean spin values of an isotropic Heisenberg rerroagnet for semi-infinite crystal and (ii) the sponta- neous magnetization of an anisotopic Heisenberg ferromagnet for monolayer and double layer. The full low temperature expansion startion with T~3/~2 term was obtained for the semi-infinite Heisenberg ferromagnet and it was shown that the spontaneous magnetization for thin films of anisotropic Heienberg ferromagnets can exhibit a uqasi-linear behaviour in certain etmperature region related ot the magnitude of the anisotropy.