Thickness Dependence of Effective Composition for Amorphous TbFe Films

An attempt is made to explain the deviation to the Fe-rich side of the ``effective'' composition of RF sputtered, amorphous TbFe films. The results indicate that the effective composition apparently varies as a function of film thickness, and this cannot be explained using the present model. A thin boundary-layer model is proposed which assumes: 1) these layers are formed at both the film-substrate and film-air boundaries; 2) this layer thickness is independent of the total film thickness; and 3) there are exchange couplings between the boundary layer and the middle layer.