Element-resolved orbital polarization in (III,Mn)As ferromagnetic semiconductors from $K$-edge x-ray magnetic circular dichroism

Using x-ray magnetic circular dichroism (XMCD), we determine the element-specific character and polarization of unoccupied states near the Fermi level in (Ga,Mn)As and (In,Ga,Mn)As thin films. The XMCD at the $\text{As}K$ absorption edge consists of a single peak located on the low-energy side of the edge, which increases with the concentration of ferromagnetic Mn moments. The XMCD at the $\text{Mn}K$ edge is more detailed and is strongly concentration dependent, which is interpreted as a signature of hole localization for low Mn doping. The results indicate a markedly different character of the polarized holes in low-doped insulating and high-doped metallic films, with a transfer of the hole orbital magnetic moment from Mn to As sites on crossing the metal-insulator transition.

Figure 1

(Color online) Resistivity versus temperature curves for the (Ga,Mn)As (G1-G4) and (In,Ga,Mn)As (I1-I3) samples used in this study.

Figure 2

(Color online) (a) $\text{As}K$ edge x-ray absorption spectrum; (b) XMCD spectra for (Ga,Mn)As samples G2 (2% Mn, as-grown, squares), G3 (5% Mn, as-grown, filled circles), G4 (5% Mn, annealed, open circles), and (In,Ga,Mn)As sample I3 (8% Mn, annealed, crosses); (c) calculated $\text{As}K$ edge x-ray absorption spectrum with Fermi energy set to $-2.0\text{eV}$ (full line) and $-2.5\text{eV}$ (points).

Figure 3

(Color online) XMCD at fixed x-ray energy of 11873 eV for sample I2 versus applied magnetic field, at a sample temperature of 10 K (squares), 35 K (circles), 57 K (stars), and 75 K (dots). The inset compares the temperature dependence of the XMCD (points) and the magnetization measured by SQUID magnetometry (line) for a fixed field of 0.1 T, normalized at the lowest temperatures.

Figure 4

(Color online) Orbital magnetic moment per As ion versus (a) saturation magnetization $M_S$ and (b) Curie temperature $T_{\text{C}}$ for a series of (Ga,Mn)As (squares) and (In,Ga,Mn)As (circles) samples. Filled symbols are for normal incidence and open symbols are for $15°$ incidence.

Figure 5

(Color online) (a) $\text{Mn}K$ edge x-ray absorption spectra and (b) XMCD spectra for (Ga,Mn)As samples G1 (1% Mn, as-grown, open squares), G2 (2% Mn, as-grown, filled squares), G3 (5% Mn, as-grown, filled circles), G4 (5% Mn, annealed, open circles), and (In,Ga,Mn)As sample I1 (8% Mn, as-grown, crosses). The vertical arrow indicates the position of the Fermi edge peak A referred to in the text.