Influence of surface treatment on the magnetic properties of ${\mathrm{Ga}}_x{\mathrm{Mn}}_{1-x}\mathrm{As}$ thin films

We present a surface science study on carefully characterized ${\mathrm{Ga}}_x{\mathrm{Mn}}_{1-x}\mathrm{As}$ films grown on $\mathrm{GaAs}\left(100\right)$, where we investigate the influence on magnetic properties of different surface cleaning procedures. X-ray magnetic circular dichroism reveals a net remnant magnetization along the (100) axis, after chemical etching is performed. The analysis of Mn $L_{2,3}$ XAS line shapes in different environment indicates that Mn in ${\mathrm{Ga}}_x{\mathrm{Mn}}_{1-x}\mathrm{As}$ behaves as a bulk impurity. By exploiting the different depth sensitivity between x-ray photoemission and x-ray absorption we observe the presence of a Mn depleted layer at the surface after etching.

Figure 1

SQUID magnetization loops with the magnetic field applied along the (100) easy magnetization axis measured at $30\mathrm{K}$. Full circles show the loop of the as grown sample. Open circles show the loop after surface preparation. The inset shows a zoom into the low field region.

Figure 2

(Color online) Left: Sketch of the experimental geometry for XPS/XAS/XMCD measurements. Right, Panel (a): Mn $L_{2,3}$ XAS spectra at room temperature of samples $S1$ as-grown (dashed line) and sample $S2$ after etching (continuous line). Panel (b): sample $S2$ etched (continuous line) compared with bcc $\mathrm{MnPt}\left(10\mathrm{\AA }\right)∕\mathrm{Fe}\left(100\right)$ (green dashed line), metallic $\mathrm{Mn}∕\mathrm{Fe}\left(100\right)$ (black dotted line), hexagonal $\mathrm{MnAs}∕\mathrm{GaAs}\left(100\right)$ (yellow dashed-dotted line), and $\mathrm{Mn}∕\mathrm{Ge}$ alloy (red dot dashed lined). All spectra have been normalized to unity for comparison.

Figure 3

Mn $L_{2,3}$ XMCD spectra and difference spectra (dotted line, multiplied by 2), at $17\mathrm{K}$, of sample $S2$. The maximum asymmetry on the $L_3$ peak is $28.5\%$, taking into account the light polarization (70%) and the tilt angle of $45°$.

Figure 4

XPS spectra of the sample $S3$ at different steps of surface preparation: from bottom to top, HCl etched, sputtered (dashed line) and annealed in oxygen (continuous line). In the inset is visible the evolution of the Mn $2p$ core level peaks, after background subtraction. A clear shift towards higher binding energy is observed in the $2p$ line after annealing.