Tuning of the average $p\text{−}d$ exchange in (Ga,Mn)As by modification of the Mn electronic structure

An important parameter of the ferromagnetism of (Ga,Mn)As alloys is the average $p\text{−}d$ exchange integral $N_0\beta$ since the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction parameter $J_{\mathrm{RKKY}}\propto {\left(N_0\beta \right)}^2$. We prove, by a detailed study of $p$-type ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$ and $n$-type ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}:\mathrm{Te}$ $(x<0.005)$ in the paramagnetic phase, that the magnitude and sign of $N_0\beta$ are strongly dependent on the local electronic configuration of the Mn ions. We find $N_0\beta >0$ (ferromagnetic coupling) in $p$-type samples where the local Mn configuration is ${\mathrm{Mn}}_{\mathrm{Ga}}^0$ $(3d^5+\text{hole})$. In $n$-type samples, $N_0\beta <0$ (antiferromagnetic coupling) with the local Mn configuration being ${\mathrm{Mn}}_{\mathrm{Ga}}^{-}$ $\left(3d^5\right)$. The average $N_0\beta$ in (Ga,Mn)As is not a material constant as widely believed. It can be tuned and can even change its sign, depending on the doping conditions of the Mn-containing layer.

Figure 1

Left: MCD spectra of GaAs:Mn (A,B) and GaAs:Mn,Te (C,D,E) samples taken at $H=1\mathrm{T}$ for A to D, $H=3\mathrm{T}$ for E. Right: corresponding Hall results.

Figure 2

Logarithmic contour plots of magnetization densities of the isolated ${\mathrm{Mn}}_{\mathrm{Ga}}^{-}$ point defect with an additional valence band hole in a (110) GaAs plane. Left: the density of the valence band hole; center: density of the $t_2\uparrow$ gap state; right: total magnetization density of $t_2\uparrow +e\uparrow$. (Two contour lines correspond to one decade in density.)

Figure 3

Left: Spin-flip Raman spectra of $p$-type GaAs:Mn (sample B); the magnetic field ranges from $0\text{to}6\mathrm{T}$ in $0.5\mathrm{T}$ steps. Right: EPR spectra at $T=4\mathrm{K}$ of GaAs:Mn,Te (samples C and E). Inset: hyperfine structure of $A^{-}$ line (sample E). Top: Schematic representation of the mechanism leading to $N_0\beta >0$ and $N_0\beta <0$.