Embedded magnetic phases in (Ga,Fe)N: the key role of growth temperature

Abstract

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 $\hat{I}\mu -$Fe${}_3$N but also by $γ'$-Fe${}_4$N and by inclusions of elemental $\hat{I}\pm$- and ${\hat{I}}^3$-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 ($x\le$ 2) phases, like $\hat{I}\P$-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.

12 pages, 11 figures