  The magnetic anisotropy of a planar array of Ga$_{x}$Fe$_{4-x}$N nanocrystals
(NCs) embedded in a GaN host is studied by ferromagnetic resonance. X-ray
diffraction and transmission electron microscopy are employed to determine the
phase and distribution of the nanocrystals. The magnetic anisotropy is found to
be primarily uniaxial with the hard axis normal to the NCs plane and to have a
comparably weak in-plane hexagonal symmetry. The origin of the magnetic
anisotropy is discussed taking into consideration the morphology of the
nanocrystals, the epitaxial relations, strain effects and magnetic coupling
between the NCs.
