Mn electronic structure and induced Ga moment in Mn-doped GaN

We use soft x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD) to examine the Mn valence, magnetic behavior, and induced Ga magnetic moment in a series of MBE-grown Mn-doped GaN films. We find two distinct magnetic states for Mn, one that is clearly Mn$^{2+}$, and another of indeterminate valence that is potentially due to Mn interstitials. A comparison of fluorescence and electron yield data suggests a depletion of Mn interstitials near the surface. A small magnetic polarization exists on the Ga site, apparently antiparallel to the Mn moment. First principle calculations suggest that most defects, such as Mn interstitials, double Mn substitutions and Ga vacancies, lead to small Ga moments that are parallel to Mn, while only the split N interstitials lead to antiparallel Ga moment. Work at the University of Wisconsin, Milwaukee was supported by NSF grant No. DMR-0094105. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science, under Contract No. W-31-109-Eng-38.