Ferromagnetic (Ga,Mn)N epilayers versus antiferromagnetic GaMn$_3$N clusters

TL;DR

This study investigates the magnetic properties of Mn-doped GaN epilayers, revealing a transition from paramagnetism to ferromagnetism with increasing Mn content and the formation of GaMn3N clusters.

Contribution

It demonstrates the growth conditions affecting Mn incorporation and identifies ferromagnetic behavior in Mg co-doped samples up to 175 K, a novel finding in this material system.

Findings

Purely substitutional GaMnN is paramagnetic.

Higher Mn leads to GaMn3N cluster formation.

Mg co-doping induces ferromagnetism up to 175 K.

Abstract

Mn-doped wurtzite GaN epilayers have been grown by nitrogen plasma-assisted molecular beam epitaxy. Correlated SIMS, structural and magnetic measurements show that the incorporation of Mn strongly depends on the conditions of the growth. Hysteresis loops which persist at high temperature do not appear to be correlated to the presence of Mn. Samples with up to 2% Mn are purely substitutional Ga$_{1-x}$Mn$_x$N epilayers, and exhibit paramagnetic properties. At higher Mn contents, precipitates are formed which are identified as GaMn$_3$N clusters by x-ray diffraction and absorption: this induces a decrease of the paramagnetic magnetisation. Samples co-doped with enough Mg exhibit a new feature: a ferromagnetic component is observed up to $T_c\sim175$ K, which cannot be related to superparamagnetism of unresolved magnetic precipitates.