Out-of-Plane Magnetic Anisotropy in Ordered Ensembles of Fe${}_y$N Nanocrystals Embedded in GaN

Phase-separated semiconductors containing magnetic nanostructures are relevant systems for the realization of high-density recording media. Here, the controlled strain engineering of Ga$\delta$FeN layers with Fe${}_y$N embedded nanocrystals (NCs) $\mathit{\text{via}}$ Al${}_x$Ga${}_{1-x}$N buffers with different Al concentration $0<x_{\mathrm{A}\mathrm{l}}<41$% is presented. Through the addition of Al to the buffer, the formation of predominantly prolate-shaped $\epsilon$-Fe${}_3$N NCs takes place. Already at an Al concentration $x_{\mathrm{A}\mathrm{l}}$,$\approx$,5% the structural properties—phase, shape, orientation—as well as the spatial distribution of the embedded NCs are modified in comparison to those grown on a GaN buffer. Although the magnetic easy axis of the cubic $\gamma$’-Ga${}_y$Fe${}_{4-y}$N nanocrystals in the layer on the $x_{\mathrm{A}\mathrm{l}}=0\mathrm{\%}$ buffer lies in-plane, the easy axis of the $\epsilon$-Fe${}_3$N NCs in all samples with Al${}_x$Ga${}_{1-x}$N buffers coincides with the $[0001]$ growth direction, leading to a sizeable out-of-plane magnetic anisotropy and opening wide perspectives for perpendicular recording based on nitride-based magnetic nanocrystals.