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 ${T}_{\text{g}}$ $(800\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C})$; (ii) superparamagneticlike---brought about mainly by ferromagnetic nanocrystals of $\ensuremath{\epsilon}{\text{-Fe}}_{3}\text{N}$ but also by ${\ensuremath{\gamma}}^{\ensuremath{'}}{\text{-Fe}}_{4}\text{N}$ and by inclusions of elemental $\ensuremath{\alpha}\text{-Fe}$, 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 ${\text{Fe}}_{x}\text{N}$ $(x\ensuremath{\le}2)$ phases, like $\ensuremath{\zeta}{\text{-Fe}}_{2}\text{N}$, and detected in samples deposited at the highest employed temperature, ${T}_{\text{g}}=950\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$. 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.