Element Resolved Spin Configuration in Ferromagnetic Manganese-Doped Gallium Arsenide

We report induced Ga and As moments in ferromagnetic ${\mathrm{G}\mathrm{a}}_{1-x}{\mathrm{M}\mathrm{n}}_x\mathrm{A}\mathrm{s}$ detected using x-ray magnetic circular dichroism at the Mn, Ga, and As $L_{3,2}$ edges. Across a broad composition range, we find As and Ga dichroism signals which indicate an As $4s$ moment coupled antiparallel to the Mn $3d$ moment, and a smaller parallel Ga $4s$ moment. The Ga moment follows that of Mn in both doping and temperature dependence. These results are consistent with recent predictions of induced GaAs host moments and support the model of carrier-mediated ferromagnetic ordering involving As-derived valence band states.

Figure 1

XAS and XMCD data taken for ${\mathrm{G}\mathrm{a}}_{0.93}{\mathrm{M}\mathrm{n}}_{0.07}\mathrm{A}\mathrm{s}$ at 30–40 K at the Mn (a), As (b), and Ga (c) $L$ edges. Data were taken in remanence by reversing the magnetization at each energy point at fixed photon helicity. For As and Ga, artifacts were removed by combining dichroism curves taken with opposite helicities.

Figure 2

(a) Hysteresis at 45 K of the Mn and Ga $L_3$ dichroism peak intensities for ${\mathrm{G}\mathrm{a}}_{0.951}{\mathrm{M}\mathrm{n}}_{0.049}\mathrm{A}\mathrm{s}$. The Mn data were taken at the energy of feature “A” in Fig. 1a, and the Ga data were taken at feature “B” in Fig. 1c. (b) Temperature dependence of the dichroism for the same sample. Open circles (main panel and inset) show the total magnetization of the same sample obtained by SQUID magnetometry.

Figure 3

Dependence of Mn and Ga XMCD signals on Mn doping.

Figure 4

Comparison of areas of As (a) and Ga (b) $2p\to 4s$ dichroism peaks. Peak areas are derived by fitting to Gaussians (upper curves, shown with data as markers) and integrating the Gaussians (lower curves). For As, higher energy $3d$ states are fit to a broad Gaussian (dashed curve) but are not included in the integration.