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

Abstract

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