Valence-state model of strain-dependent Mn L2,3 x-ray magnetic circular dichroism from ferromagnetic semiconductors

We present a valence-state model to explain the characteristics of a recently observed pre-edge feature in Mn L-3 x-ray magnetic circular dichroism (XMCD) of ferromagnetic (Ga,Mn) As and (Al,Ga,Mn) As thin films. The prepeak XMCD shows a uniaxial anisotropy, contrary to the cubic symmetry of the main structures induced by the crystalline electric field. Reversing the strain in the host lattice reverses the sign of the uniaxial anisotropy. With increasing carrier localization, the prepeak height increases, indicating an increasing 3d character of the hybridized holes. Hence, the feature is ascribed to transitions from the Mn 2p core level to unoccupied p-d hybridized valence states. The characteristics of the prepeak are readily reproduced by the model calculation taking into account the symmetry of the strain-, spin- orbit-, and exchange-split valence states around the zone center.