Single ion anisotropy of Mn-doped GaAs measured by electron paramagnetic resonance

Abstract

An electron-paramagnetic-resonance (EPR) study of molecular-beam-epitaxy-grown Mn-doped GaAs is presented. The resolved fine structure in insulating ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ allows us to evaluate the crystal-field parameters of the spin Hamiltonian. The exchange narrowing of the structure, which accompanies the presence of carriers, indicates long-range exchange interaction. The obtained cubic constant is $a=\ensuremath{-}14.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4} {\mathrm{cm}}^{\ensuremath{-}1}.$ The axial field parameter D increases with Mn concentration x, i.e., with the strain of ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ layers. Extrapolation of D shows that the single-ion anisotropy is the small contribution to the total magnetic anisotropy that is observed in ferromagnetic layers with greater Mn and holes concentrations. The analysis of the EPR linewidth shows that native defects of the concentration of $5\ifmmode\times\else\texttimes\fi{}{10}^{19} {\mathrm{cm}}^{\ensuremath{-}3},$ but not the Mn ions, are the main origin of crystal-field fluctuations.