Photoemission studies of magnetic semiconductors

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* Soft x-ray absorption (XAS) and soft x-ray magnetic circular dichroism (XMCD) studies at the Co 2p core absorption edges of Zn1-xCoxO (x=0.05) prepared by the pulsed laser deposition (PLD) method were performed and the obtained spectra were analyzed using cluster-model calculations. We have found that the temperature and the magnetic field dependences of the XMCD intensity were very different from non-interacting Co ions and that ferromagnetic and antiferromagnetic interactions between the Co ions coexist inhomogeneously.* XAS and resonance photoemission studies at the Mn 2p core absorption edges of Ga1-xMnxN prepared by the molecular-beam epitaxy (MBE) method were performed, and the obtained spectra were analyzed using cluster-model calculations. We found that the valence of the Mn ion was 2+ and that the Mn 3d states were largely distributed within the valence band of the GaN host. Acceptor levels formed by the Mn doping above the valence-band maximum Mn were found to be occupied b … More y electrons, indicating that the high-temperature ferromagnetism predicted by theory was nor realized because of the compensation effect.* XAS, XMCD and resonance photoemission studies were performed at the Cr 2p core absorption edges of Ga1-xCrxN (x=0.015). The Cr 2p XAS spectra indicated that the Cr was in the 3+ valence state. The Cr 3d partial density of states (PDOS) were largely distributed within the band gap of GaN, in striking contrast with Ga1-xMnxN. The Cr 3d PDOS was found to be suppressed at the Fermi level, and no Fermi-edge feature as predicted by band-structure calculations was observed.* XAS and XMCD measurements were made on Zn1-xVxO (x=0.05) which exhibited weak ferromagentism. The V ions substituting Zn2+ were found to be responsible for the magnetic properties. From comparison of the XMCD spectra with the magnetic susceptibility, we found that 10% of V ions were paramagnetic and 90 % were strongly coupled with each other antiferromagnetically. Furthermore, the paramagnetic V ions were found to be influenced by the axial crystal field of the hexagonal ZnO host. Less