Valence band orbital polarization in III-V ferromagnetic semiconductors

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 $\mathrm{As}K$ absorption edge, yielding an $\mathrm{As}4p$ orbital magnetic moment of around $-0.1{\mu }_B$ per valence band hole, which is strongly influenced by strain, indicating its crucial influence on the magnetic anisotropy. The dichroism at the $\mathrm{Ga}K$ edge is much weaker. The $K$ edge XMCD signals for Mn and As both have positive sign, which indicates the important contribution of $\mathrm{Mn}4p$ states to the $\mathrm{Mn}K$ edge spectra.

Figure 1

(Color online) (a) XMCD spectra (drawn lines, left axes) and x-ray absorption spectra (dashed lines, right axes) for (a) $\mathrm{As}K$ edge of (Ga,Mn)As, (b) $\mathrm{As}K$ edge of (In,Ga,Mn)As, and (c) $\mathrm{Ga}K$ edge of (In,Ga,Mn)As. The thick red (gray) lines give the XMCD for normal incidence, and the thin blue (black) line in (b) gives the XMCD for grazing incidence.

Figure 2

(Color online) $\mathrm{Mn}K$ edge XMCD spectra (drawn lines, left axis) and x-ray absorption spectra (dashed lines, right axis) for (Ga,Mn)As [thin blue (black) lines] and (In,Ga,Mn)As [thick red (gray) lines].