Thermal stability of high frequency properties of gradient-composition-sputtered FeCoHf films with and without stripe domains

Abstract

A systematic study on the thickness dependence of dynamic magnetic properties and their thermal stability behaviors of FeCoHf thin films grown by gradient-composition sputtering technique was carried out. The critical thickness for the formation of stripe domain structures at room temperature was found to be around 120 nm based on the appearance of the multiple resonance peaks and the shape of the magnetization curves. For the films with thicknesses less than 90 nm, the ferromagnetic resonance frequency and in-plane magnetic anisotropy are increased with the increasing of temperature; however, for the films with thicknesses in the range from 90 nm to 120 nm, the ferromagnetic resonance frequency is reduced with temperature and the secondary peak appears as the temperature is raised suggesting an evolution of stripe domains. For the films with stripe domains at room temperature, the ferromagnetic resonance frequency is also decreased with increasing temperature, and in some cases, there is a splitting up of the resonance peaks indicating that there is a change in the stripe domain states when the sample is heated up. All the results are discussed considering the contribution of stress-induced magnetic anisotropy and the increasing of a weak perpendicular magnetic anisotropy.