Effects of the external field and interlayer coupling on the spin reorientation of magnetic thin films

Abstract

The spin reorientation of ferromagnetic thin films with magnetic single-ion anisotropies is studied within the framework of the many-body Green-function technique. We investigate the effects due to the perpendicular external field and the anisotropic interface/intraface couplings on the magnetization reorientation transition in thin magnetic films consisting of up to 6 monolayers. The relative magnetization (RM) and various anisotropies under different conditions are calculated as functions of the temperature, film thickness, as well as the external field for arbitrary spin. The nearest-neighbor (NN) intraface coupling constant is treated as a parameter, whose value is determined by the Curie temperature of the bulk magnet. It is found that under the external field, the RM near the critical point exhibits behavior different from what is expected in the absence of the field. In particular, it is illustrated that an applied field increases the critical thickness for the magnetization reorientation transition (MRT). A slight change of the surface anisotropy ${D}_{s}$ may change the nature of transition between the ferromagnetic ordered-disorder transition and MRT. The effects of various exchange coupling constants, however, can only shift the transition temperature but cannot change the nature of the transition. Finally, we find that in Fe films with perpendicular magnetization, the ferromagnetic (antiferromagnetic) interlayer coupling constants do not coexist with the antiferromagnetic (ferromagnetic) intralayer coupling constants. The nature of both the interlayer and intralayer coupling must be the same, either ferromagnetic or antiferromagnetic.