FERROMAGNETIC PRECIPITATES IN OXYGEN CONTAMINATED GaN:Fe

Abstract

Ferromagnetic MOCVD grown GaN films doped with about 1% Fe and unintentionally contaminated with oxygen were investigated by electron spin resonance. Simultaneously with the paramagnetic resonance of isolated Fe 3+ on Ga sites numerous ferromagnetic resonance (FMR) signals were detected. The narrow linewidths (below 50 G at the easy magnetization orientation) indicated a well-defined crystallographic structure. In all investigated samples the presence of spheroidal magnetite ( Fe 3 O 4) precipitates was detected. The fact that the easy and hard axes changed direction at 105 K and the FMR signal in X band disappeared exactly below the Vervey transition temperature confirmed the identification unambiguously. Bcc iron particles with dimensions small enough to influence the magnetocrystalline anisotropy constant were also observed, but only in samples less contaminated with oxygen. Precipitates of both phases were arbitrarily oriented with respect to the GaN crystallographic axes. In addition, FMR signals related to two distinctly different hexagonally ordered phases could be distinguished, both with the easy magnetization directions lying in the basal plane. The high uniaxial and small in-plane anisotropy constants of one of them are close to those observed in small diameter hematite (α- Fe 2 O 3) nanoparticles. The other hexagonal phase has a Curie temperature of about 360 K and is, yet, unidentified.