The local chemistry, structure, and magnetism of (Ga,Fe)N nanocomposites grown by metal organic vapor phase epitaxy is studied by high resolution synchrotron x-ray diffraction and absorption, transmission electron microscopy, and superconducting quantum interference device magnetometry as a function of the growth temperature $T_{ \mathrm{ g}}$. Three contributions to the magnetization are identified: i) paramagnetic -- originating from dilute and non-interacting Fe$^{ 3+}$ ions substitutional of Ga, and dominating in layers obtained at the lowest considered $T_{ \mathrm{ g}}$ (800$^{ \circ}$C); ii) superparamagnetic-like -- brought about mainly by ferromagnetic nanocrystals of $\epsilon-$Fe$_3$N but also by $\gamma'$-Fe$_4$N and by inclusions of elemental $\alpha$- and $\gamma$-Fe, and prevalent in films obtained in the intermediate $T_{ \mathrm{ g}}$ range; iii) component linear in the magnetic field and associated with antiferromagnetic interactions -- found to originate from highly nitridated Fe$_x$N ($x \leq$ 2) phases, like $\zeta$-Fe$_2$N, and detected in samples deposited at the highest employed temperature, $T_{ \mathrm{ g}}$ = 950$^{ \circ}$C. Furthermore, depending on $T_{ \mathrm{ g}}$, the Fe-rich nanocrystals segregate towards the sample surface or occupy two-dimensional planes perpendicular to the growth direction.
Categories: cond-mat.mtrl-sci