Ferromagnetic moment and antiferromagnetic coupling in (Ga,Mn)As thin films

We demonstrate that carefully prepared (Ga,Mn)As films can show large magnetic moments per atom across a wide range of Mn concentrations, indicating almost full participation of the Mn in the ferromagnetism. Applying sum rules to Mn L2,3 x-ray magnetic circular dichroism (XMCD) spectra yields a magnetic moment per Mn of around 4.5μB, including a small positive orbital moment. We also present direct evidence for antiferromagnetic coupling between interstitial and substitutional Mn in unannealed (Ga,Mn)As. The Mn L2,3 x-ray absorption line shapes display no sizeable site or concentration dependence, but in unannealed (Ga,Mn)As the XMCD signal is significantly smaller, and increases linearly under high magnetic fields.