The magnetic properties of Zn 1−x Co x O ͑x = 0.07 and 0.10͒ thin films, which were homoepitaxially grown on a ZnO͑0001͒ substrates with varying relatively high oxygen pressure, have been investigated using x-ray magnetic circular dichroism ͑XMCD͒ at Co 2p core-level absorption edge. The line shapes of the absorption spectra are the same in all the films and indicate that the Co 2+ ions substitute for the Zn sites. The magneticfield and temperature dependences of the XMCD intensity are consistent with the magnetization measurements, indicating that except for Co there are no additional sources for the magnetic moment, and demonstrate the coexistence of paramagnetic and ferromagnetic components in the homoepitaxial Zn 1−x Co x O thin films, in contrast to the ferromagnetism in the heteroepitaxial Zn 1−x Co x O films studied previously. The analysis of the XMCD intensities using the Curie-Weiss law reveals the presence of antiferromagnetic interaction between the paramagnetic Co ions. Missing XMCD intensities and magnetization signals indicate that most of Co ions are nonmagnetic probably because they are strongly coupled antiferromagnetically with each other. Annealing in a high vacuum reduces both the paramagnetic and ferromagnetic signals. We attribute the reductions to thermal diffusion and aggregation of Co ions with antiferromagnetic nanoclusters in Zn 1−x Co x O.
We have investigated the electronic structure of Cr-and Mn-doped GaN using photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS). Cr and Mn XAS at the L-edge have indicated that the Cr and Mn ions are in the tetrahedral crystal field and that their valences are trivalent and divalent, respectively. Upon Cr and Mn doping into GaN, new states were found to form in the band-gap region of GaN. Resonant photoemission spectroscopy (RPES) has revealed that the main structure of the Cr 3d partial density of states (PDOS) appears within the band gap of GaN while that of the Mn 3d PDOS appears within the valence band of GaN and as a shoulder above the valence-band maximum of GaN, indicating that the character of the doping-induced states is different between Ga 1-x Cr x N and Ga 1-x Mn x N.
We have performed an in situ depth profile study of Mn-doped GaN prepared by a low temperature thermal diffusion method using photoemission and x-ray absorption spectroscopy. It was revealed from the core-level photoemission measurements that Mn ions are diffused into a deep ͑ϳ70 Å͒ region of the GaN substrates and that the line shapes of Mn 3d partial density of states obtained by resonant photoemission measurements were close to that of Ga 1−x Mn x N thin films grown by molecular-beam epitaxy. From x-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements at the Mn L edge, it was revealed that the doped Mn ions were in the divalent Mn 2+ state and primarily paramagnetic. In magnetization measurements, weak hysteresis was detected in samples prepared using p-type GaN substrates while samples using n-type GaN substrates showed only paramagnetism.
A study of the growth of Lu 2 O 3 on Si(001) by synchrotron radiation photoemission and transmission electron microscopy Surface electronic structure in transition-metal (Cr and Mn) doped GaAs (001) studied by in situ photoemission spectroscopy Appl.We have performed a depth profile study of thermally diffused Mn/GaAs ͑001͒ interfaces using photoemission spectroscopy combined with Ar + -ion sputtering. We found that Mn ion was thermally diffused into the deep region of the GaAs substrate and completely reacted with GaAs. In the deep region, the Mn 2p core-level and Mn 3d valence-band spectra of the Mn/GaAs ͑001͒ sample heated to 600°C were similar to those of Ga 1−x Mn x As, zinc-blend-type MnAs dots, and/or interstitial Mn in tetrahedrally coordinated by As atoms, suggesting that the Mn atoms do not form any metallic compounds but are tetrahedrally coordinated by ligand atoms, and Mn 3d states are hybridized with ligand orbitals lized but were hybridized with the electronic states of the host GaAs. Ferromagnetism was observed in the dilute Mn phase.
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