Single ion anisotropy of Mn doped GaAs measured by EPR

Electron paramagnetic resonance (EPR) study of MBE grown Mn doped GaAs is presented. The resolved fine structure allows us to evaluate the crystal field parameters of the spin Hamiltonian. The obtained cubic constant is a= -14.1 10^-4/cm. The axial field parameter, D, increases with Mn concentration, x, i.e., with the strain of (Ga,Mn)As layers. Extrapolation of D shows that the single ion anisotropy is the important contribution to the magnetic anisotropy which is observed in ferromagnetic layers with greater Mn concentrations. The analysis of the EPR linewidth shows that native defects of the concentration of 5 10^19/cm^3, but not the Mn ions, are the main origin of crystal field fluctuations.