Ferromagnetic Ga _{1 − <i>x</i>} Mn _<i>x</i> N epilayers <i>vs.</i> antiferromagnetic GaMn ₃ N clusters

Abstract

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