铁超薄膜的铁磁相变和垂直磁各向异性

Ferromagnetic Phase Transition and Perpendicular Magnetic Anisotropy in 1～8 Monolayer Fcc Iron Films

根据表面原子自旋倾向垂直于表面取向的海森堡模型，运用格林函数方法讨论了１～８层面心铁磁薄膜的铁磁相变和垂直磁各向异性．证明了铁磁薄膜其序参数（自发磁化）是随薄膜中空间位置而变化的，而薄膜中不同位置的居里温度是相同的．计算了表面各向异性常数Ｋｓ（Ｔ），有效体各向异性常数Ｋｖ（Ｔ）和形状各向异性常数Ｋｄ（Ｔ）与温度的关系，证明了在一定的温度和厚度下薄膜存在垂直剩磁（Ｋｖ（Ｔ）－Ｋｄ（Ｔ）＞０），在弱表面各向异性（ＳＡ）的情况下，７层面心铁磁薄膜仍具有垂直磁化。

The ferromagnetic phase transition and perpendicular magnetic anisotropy in one to eight monolayer fcc iron films are studied by the Green-function method based upon the Heisenberg model with perpendicular spin orientation of the atoms at the surfaces. The model calculation shows that the order parameter(spontaneous magnetizaton) changes with the atomic planes in the ferromagnetic films but the Curie temperatures of the atomic planes are all the same. We also calculate the surface anisotropy constant K s(T) , the effective volume anisotropy constant K v(T) and the shape anisotropy constant ( K v(T)-K d(T) >0) for an intermediate range of thickness of ultrathin films and temperature and prove that seven monolayer fcc iron film still has perpendicular remanence which agrees with the experiments for the ultrathin films of fcc Fe on Cu(001).