Magnetic properties and electronic origin of the interface between dilute magnetic semiconductors with orthogonal magnetic anisotropy

Controlling changes in magnetic anisotropy across epitaxial film interfaces is an important prerequisite for many spintronic devices. For the canonical dilute magnetic semiconductor GaMnAs, magnetic anisotropy is highly tunable through strain and doping, making it a fascinating model system for exploration of anisotropy control in a carrier-mediated ferromagnet. Here, we have used transmission electron microscopy and polarized neutron reflectometry to characterize the interface between GaMnAs-based layers designed to have anisotropy vectors oriented at right angles from one another. For a bilayer of ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x{\mathrm{As}}_{1-y}{\mathrm{P}}_y$ and ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$, we find that the entirety of the ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$ layer exhibits in-plane magnetic anisotropy and that the $majority$ of the ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x{\mathrm{As}}_{1-y}{\mathrm{P}}_y$ exhibits perpendicular anisotropy. However, near the ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$ interface, we observe a thin Mn-rich region of the nominally perpendicular ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x{\mathrm{As}}_{1-y}{\mathrm{P}}_y$ that instead exhibits $in-plane$ anisotropy. Using first-principles energy considerations, we explain this sublayer as a natural consequence of interfacial carrier migration.

Figure 1

Structural characterization of the annealed ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x{\mathrm{As}}_{1-y}{\mathrm{P}}_y/{\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$ bilayer sample. (a) Cross-sectional high-angle annular dark-field TEM image viewed along the [110] zone-axis projection of the GaAs (001) substrate. (b) XRD spectrum along the (00L) direction. The red curve is a simulated diffraction pattern for the quantitative structure described in the main text and is intentionally offset from the data for clarity. (c) Reciprocal space map taken at the asymmetric ($\overline{2}\overline{2}4$) Bragg peak.

Figure 2

In-plane magnetization vs in-plane applied magnetic field for the (Ga,Mn)(As,P) bilayer. The sweep starts at the top right-hand quadrant, descending down the top branch, and then ascending up the bottom branch. Numbered points correspond to PNR measurements and the order in which they were collected. The fourth PNR measurement was conducted at $+500\mathrm{mT}$, outside the domain of the figure.

Figure 3

Fitted PNR data plotted as spin asymmetry, measured at 5 K for the four field conditions described above (a)–(d).

Figure 4

Scattering length density depth profiles determined from fits to the PNR data. Dashed vertical line delineates the interface between the GaMnAs and GaMnAsP as revealed by TEM. (a) Nuclear profiles indicating chemical interfaces between the layers. (b) Zoom-in of (a), highlighting the chemically distinct interfacial GaMnAsP sublayer. (c) Field-dependent magnetization depth profiles. Error bars on the profiles represent $95\%$ confidence intervals of the fit parameter.