Magnetic Anisotropy Studies of FeyN Nanocrystals Embedded in GaN

Doping of GaN with Fe atoms above 0.4% concentration leads to crystallographic phase separation and to the self-assembly of Fe-rich nanocrystals (NCs) with stoichiometry and magnetic characteristics imposed by the growth conditions. Here, we report on the studies of magnetic anisotropy of GaδFeN layers with Fe
y
N embedded nanocrystals controlled by strain engineering via Al
x
Ga
1−x
N buffers with different Al concentration 0 ≤ x
Al
≤ 41%. Already for x
Al
< 5% the structural properties: phase, shape, orientation - as well as the spatial distribution of the embedded NCs are modified in comparison to those of the NCs stabilized in GaδFeN on GaN. Our study shows that although the magnetic easy axis of the cubic γ’-Ga
y
Fe
4−y
N nanocrystals lies in-plane of the layer, the easy axis of hexagonal ε-Fe
3
N NCs formed in all samples with x
Al
> 0 coincides with the [0001] growth direction. This leads to a sizeable out-of-plane magnetic anisotropy and opens wide perspectives for perpendicular recording based on nitride-based magnetic nanocrystals. Our study yields the first direct determination of the temperature dependence of magnetocrystalline anisotropy parameter ε-Fe
3
N.