Ferromagnetism in GaN induced by Fe ion implantation

We report about magnetic and structural studies on p-type GaN implanted with 57Fe with fuences from 1*10^16cm^-2 to 1.6*10^17cm^-2 at different temperatures and subsequently subjected to thermal treatment. X-ray diffraction, transmission electron microscopy, conversion electron Mössbauer spectroscopy and superconducting quantum interference device magnetometry were used for the crystallographic, electronic and magnetic characterization of the samples. Room temperature ferromagnetism was observed in GaN after implantation at 623 K with different fluences and is mainly ascribed to alpha-Fe precipitations. An additional contribution to ferromagnetic signal is observed in a Mössbauer spectrum and as a magnetization loop in SQUID in sample implanted with lowest fluence at 623 K which cannot be related to alpha-Fe. In samples implanted with low fluences at RT no ferromagnetism was observed by means of SQUID. However, in CEMS a 6.8 T magnetic hyperfine field was used to fit the experimental spectrum and is discussed in terms of possible origin. Samples implanted at 240 K do not exhibit ferromagnetic properties. Precipitation of alpha-Fe was successfully reduced by decreasing the implantation temperature, however this was accompanied by an enhanced crystal damage. Annealing between 973 K and 1123 K resulted in most cases predominantly in the formation of alpha-Fe-clusters. Thermal treatment brought no significant recover of the crystallinity as it was verified by RBS channeling measurements.