Figure 1

(Color online) (a) High-resolution TEM images of a bilayer sample. (b) Atomic force microscope image of the top MnAs layer. (c) Depiction of a partial domain-wall configuration in ${\text{Ga}}_{1-x}{\text{Mn}}_x\text{As}$, with spins continuously rotating as a function of the distance from the interface. Beyond a certain depth $t_1$, a complete domain $\left(t_2\right)$ forms.Reuse & Permissions

Figure 2

(Color online) (a) Temperature-dependent remanent magnetization $M\left(T\right)$ for bilayer samples with three different ${\text{Ga}}_{1-x}{\text{Mn}}_x\text{As}$ thicknesses as indicated on the plot (series A). The ${\text{Ga}}_{1-x}{\text{Mn}}_x\text{As}$ composition is $x=0.06$ and the MnAs thickness is $t_{\text{MA}}=12\text{nm}$. (b) Minor hysteresis loop for the bilayer samples with $t_{\text{GMA}}=50\text{nm}$ (green squares) and $t_{\text{GMA}}=80\text{nm}$ (blue triangles). Data are taken at $T=4.2\text{K}$. (c) Exchange field versus ${\text{Ga}}_{1-x}{\text{Mn}}_x\text{As}$ thickness, showing that $H_{\text{E}}\propto {\left(t_{\text{GMA}}\right)}^{-1}$. Data are taken at $T=4.2\text{K}$. (d) Coercivity and exchange field as a function of temperature for a high Mn composition $\text{MnAs}/{\text{Ga}}_{1-x}{\text{Mn}}_x\text{As}$ bilayer with $t_{\text{GMA}}=50\text{nm}$ and $x=0.16$.Reuse & Permissions

Figure 3

(Color online) (a) Minor hysteresis loops of three bilayer samples with varying composition $x=0.05,0.07,0.16$ (series B). In these three samples, $t_{\text{GMA}}=30\text{nm}$ and $t_{\text{MA}}=8\text{nm}$. The magnetization is shown per unit volume with the MnAs signal subtracted out. Data are taken at $T=4.2\text{K}$. (b) Exchange field $\left(H_{\text{E}}\right)$ and coercivity $\left(H_c\right)$ as a function of the saturated magnetization. Data are taken at $T=4.2\text{K}$. (c) Temperature-dependent remanent magnetization $M\left(T\right)$ for bilayer samples with different MnAs layer thicknesses in the range $1\lesssim t_{\text{MA}}\lesssim 4\text{nm}$ (series C). The ${\text{Ga}}_{1-x}{\text{Mn}}_x\text{As}$ layer has a thickness $t_{\text{GMA}}=30\text{nm}$ and composition $x=0.06$. The magnetization is shown per unit area. (d) Exchange field versus MnAs layer thickness showing critical thickness between 2 and 3 nm. The different symbols refer to two different nonrotated growths. Data are taken at $T=4.2\text{K}$.Reuse & Permissions

Figure 4

(Color online) (a) Minor loops for two trilayer samples, one with an undoped spacer and one with a Be-doped spacer. Data are taken at $T=4.2\text{K}$. The ${\text{Ga}}_{1-x}{\text{Mn}}_x\text{As}$, MnAs, and spacer-layer thicknesses are $t_{\text{GMA}}=30\text{nm}$, $t_{\text{MA}}=12\text{nm}$ and $t_{\text{spacer}}=3\text{nm}$, respectively. (b) Exchange field $\left(H_{\text{E}}\right)$ and coercivity $\left(H_c\right)$ in ${\text{Ga}}_{1-x}{\text{Mn}}_x\text{As}/p\text{-GaAs}/\text{MnAs}$ trilayers versus $p$-GaAs spacer-layer thickness (series D). Here, $t_{\text{GMA}}=30\text{nm}$ and $t_{\text{MA}}=10\text{nm}$. Data are taken at $T=4.2\text{K}$. The solid line shows a fit of the variation in $H_{\text{E}}$ vs $t_{\text{spacer}}$ to an exponential decay: $H_{\text{E}}\propto \text{exp}\left(-\alpha t_{\text{spacer}}\right)$. (c) Temperature-dependent magnetization $M\left(T\right)$ for bilayer and single-layer control sample. These measurements are taken while warming up in a field of 200 Oe. (d) Same as in (c) with the added etched sample showing that $T_{\text{C}}$ did not change and with added annealed control sample showing very similar increase in $T_{\text{C}}$. The unusual shape of the $M\left(T\right)$ at lower temperatures results from temperature-dependent changes in the easy axis.Reuse & Permissions