Lattice sites, charge states and spin-lattice relaxation of Fe ions in 57 Mn + implanted GaN and AlN

The lattice sites, valence states, resulting magnetic behaviour and spin-lattice relaxation of Fe ions in GaN and AIN were investigated by emission Mossbauer spectroscopy following the implantation of radioactive Mn-57(+) ions at ISOLDE/CERN. Angle dependent measurements performed at room temperature on the 14.4 keV gamma-rays from the Fe-57 Mossbauer state (populated from the Mn-57/beta(-) decay) reveal that the majority of the Fe ions are in the 2+ valence state nearly substituting the Ga and Al cations, and/or associated with vacancy type defects. Emission Mossbauer spectroscopy experiments conducted over a temperature range of 100-800 K show the presence of magnetically split sextets in the "wings" of the spectra for both materials. The temperature dependence of the sextets relates these spectral features to paramagnetic Fe3+ with rather slow spin-lattice relaxation rates which follow a T-2 temperature dependence characteristic of a two-phonon Raman process. (C) 2015 Elsevier B.V. All rights reserved.