  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.
