S. Senba

IV-VI diluted magnetic semiconductor Ge1-xmnxTe epilayer grown by molecular beam epitaxy

Growth of the IV-VI diluted magnetic semiconductor Ge1−xMnxTe by molecular beam epitaxy is reported. The epitaxial growth of Ge1−xMnxTe (x=0.13) on BaF2 (111) with a GeTe buffer layer is confirmed by x-ray diffraction and reflection high-energy electron diffraction. The ferromagnetic order is clearly established by the magnetization and magnetotransport measurements. The Curie temperature of 100K is obtained for the hole concentration of 7.86×1020cm−3. The existence of the strong p-d exchange which gives rise to the ferromagnetic order is revealed by the hard x-ray photoemission measurements.

Local environment of Mn atoms in IV-VI ferromagnetic semiconductor Ge1−xMnxTe

MnL2,3 x-ray absorption and magnetic circular dichroism study has been performed on IV-VI ferromagnetic semiconductor Ge1−xMnxTe with different Mn compositions x=0.12, 0.32, 0.51, and 1. The absorption and dichroism line shapes are found to be almost independent of the Mn composition, suggesting that the local chemical environment of Mn atoms is the same for Ge1−xMnxTe with the wide range of x. On the basis of the configuration interaction analysis for a MnTe6 cluster, the electronic structure parameters such as the p‐d hybridization and the p‐d exchange constant have been estimated.

UV emission spectrometer using a non-periodic grating

A UV emission spectrometer using a non-periodic spherical grating has been designed, which can be attached to the linear or helical undulator beamlines of the HiSOR light source at the Hiroshima Synchrotron Radiation Centre. The useful range of emitted photons from 10 to 100 eV is covered by two gratings with nominal groove spacings of 1/600 and 1/1200 mm. The energy resolution with a 100 micro m entrance slit width and the 1/600 mm grating is better than 0.2 eV below 50 eV.

Resonant photoemission spectroscopy in the Mn 2p-3d excitation region of NiAs-type MnTe

Resonant photoemission experiments in the Mn 2 p -3 d excitation region of NiAs-type MnTe have been performed. The Mn 3 d , 3 p and 3 s photoemission intensities have shown remarkable resonant enhancements near the Mn 2 p -3 d threshold. Their resonant behaviors are compared with the theoretical spectra on the basis of a cluster model taking account of intraaomic multipole interactions for the Mn 3 d -3 d and 3 d -core hole orbitals, and the hybridization between the Mn 3 d and ligand p -orbitals. Calculated spectra are in qualitative agreement with experimental results except for a broad structure around 20 eV below the valence-band maximum.

Local clusters in a distorted rocksalt gete crystal found by X-ray fluorescence holography

A Ge Kα X-ray fluorescence holography (XFH) measurement was performed on a single-crystal GeTe film with a deformed rocksalt (rhombohedral) lattice, for which careful analyses and observations of the reconstructed atomic images were needed. The three-dimensional atomic images obtained around the central Ge atom were compared with the theoretical images obtained from a simulated hologram in the full sphere range and in the limited θ range (0 < θ < 74°), as in the experiment. It was found that reliable atomic images were realized only when neighboring atoms are located on the surface side of the central Ge atom. GeTe3 clusters were found by XFH, which cannot be easily detected by diffraction, and confirmed by ab initio molecular dynamics simulation.

Electronic structure of MnSb and MnP

Abstract We have investigated the valence-band and conduction-band electronic structure of MnSb and MnP by means of ultraviolet photoemission and inverse-photoemission spectroscopies. The photoemission and inverse-photoemission spectra are qualitatively consistent with the results of band-structure calculations. The spectral shapes are substantially different between MnSb and MnP, which indicates that the Mn 3d electrons in MnP are more itinerant than those in MnSb.

Distorted and Undistorted Atomic Sites in a Ferromagnetic Semiconductor Ge0.6Mn0.4Te Film Determined by X-ray Fluorescence Holography

Local atomic structures around Ge and Mn atoms in a ferromagnetic semiconductor Ge0.6Mn0.4Te thin film were investigated by performing Ge and Mn Kα X-ray fluorescence holographic experiments. The obtained three-dimensional atomic images revealed that the local structure around Mn formed a rock salt lattice, whereas the lattice around Ge was strongly distorted, which is reflected by a rhombohedral structure of GeTe. The undistorted rock salt environment around the Mn atoms is considered to be a key factor allowing for this alloy to exhibit high-temperature ferromagnetism.

MN 2P-3D RESONANT PHOTOEMISSION SPECTROSCOPY OF MNY (Y = S, SE, TE)

Abstract MnY (Y = S, Se, Te) compounds have been studied by resonant photoemission near the Mn 2p–3d threshold in the Mn 3d, 3p and 3s emission region. The basic resonant behaviors of the spectra of MnY are rather similar to each other. The experimental spectra are well reproduced by the calculation for MnTe on the basis of a cluster model taking account of the intra-atomic multiple electron-electron interaction and the p-d hybridization, except for a broad structure around 20 eV below the valence-band maximum.

Soft X-ray emission spectroscopy of NiAs-type MnTe at the Mn 2p core threshold

Abstract Resonant soft X-ray emission spectra of NiAs-type MnTe have been measured near the Mn 2p threshold using synchrotron radiation. The spectra consist of two structures due to elastic and inelastic scatterings and their relative intensity depends strongly on the excitation photon energy. The inelastic scattering peak around 3–4 eV below the elastic scattering peak can be attributed to d-d * excitation. In order to interpret the resonant behaviour, we have calculated the soft X-ray emission spectra of NiAs-type MnTe on the basis of a cluster model including electron-electron interactions and p-d hybridization. The theoretical results reproduce the basic structures of the experimental spectra, through we notice a difference in their relative intensities.

Ultraviolet inverse-photoemission and photoemission spectroscopies of zincblende MnTe

Abstract Conduction-band and valence-band structures of zincblende MnTe(1 1 1) epitaxial films have been investigated by means of ultraviolet inverse-photoemission and photoemission spectroscopies, respectively. We have directly estimated a Mn 3d spin-exchange splitting energy of (6.9 ± 0.2) eV. This value is in agreement with those of Cd 1− x Mn x Te and Zn 1− x Mn x Te, but is slightly larger by 0.3 eV than that of NiAs-type MnTe.