Competition between cubic and uniaxial magnetic anisotropy in GaMnAs at low Mn concentrations

We study the dependence of the cubic and uniaxial magnetic anisotropy terms in GaMnAs on hole concentration $p$ and temperature $T$. The Ga$_{0.99}$Mn$_{0.01}$As layers were grown on ZnSe buffers deposited on GaAs substrates, and co-doped by Be in the range 3.0x10$^{19} \quad < \quad p \quad <$ 8.5x10$^{19 }$cm$^{-3}$. Due to small lattice mismatch the uniaxial and cubic anisotropy terms in these samples were comparable. The magnetic anisotropy was studied by polar magneto-optical Kerr effect, which allowed us to monitor the easy axis of magnetization. The results showed that the cubic anisotropy is highly sensitive to both $p$ and $T$. Specifically, in samples with high $p$ the cubic anisotropy term is dominant at low $T$, but decreases rapidly as $T$ increases. In sharp contrast, uniaxial anisotropy shows a much weaker dependence on $p$ and $T$, thus dominating at temperatures close to T$_{C}$ even in samples with high $p$. These results open the possibility of engineering magnetic anisotropy and the magnetization reversal process in GaMnAs by controlling $T $and/or $p$.