Perpendicular magnetization reversal, magnetic anisotropy, multi-step spin switching, and domain nucleation and expansion in Ga1-xMnxAs films
We present a comprehensive study of the reversal process of perpendicular magnetization in thin layers of the ferromagnetic semiconductor Ga1-xMnxAs. For this investigation we have purposely chosen Ga1-xMnxAs with a low Mn concentration (x ~ 0.02), since in such specimens contributions of cubic and uniaxial anisotropy parameters are comparable, allowing us to identify the role of both types of anisotropy in the magnetic reversal process. As a first step we have systematically mapped out the angular dependence of ferromagnetic resonance in thin Ga1-xMnxAs layers, which is a highly effective tool for obtaining the magnetic anisotropy parameters of the material. The process of perpendicular magnetization reversal was then studied by magneto-transport (i.e., Hall effect and planar Hall effect measurements). These measurements enable us to observe coherent spin rotation and non-coherent spin switching between the (100) and (010) planes. A model is proposed to explain the observed multi-step spin switching. The agreement of the model with experiment indicates that it can be reliably used for determining magnetic anisotropy parameters from magneto-transport data. An interesting characteristic of perpendicular magnetization reversal in Ga1-xMnxAs with low x is the appearance of a double hysteresis loops in the magnetization data. This double-loop behavior can be understood by generalizing the proposed model to include the processes of domain nucleation and expansion.