  The element-specific technique of x-ray magnetic circular dichroism (XMCD) is
used to directly determine the magnitude and character of the valence band
orbital magnetic moments in (III,Mn)As ferromagnetic semiconductors. A distinct
dichroism is observed at the As K absorption edge, yielding an As 4p orbital
magnetic moment of around -0.1 Bohr magnetons per valence band hole. This is
strongly influenced by strain, indicating its crucial influence on the magnetic
anisotropy. The dichroism at the Ga K edge is much weaker. The K edge XMCD
signals for Mn and As both have positive sign, which indicates the important
contribution of Mn 4p states to the Mn K edge spectra.
