No abstract

The (GeTe)1−γ–(Sb2Te3)γ pseudobinary system has, over almost its entire composition range, two kinds of crystalline phase: one is a metastable phase with a NaCl-type structure and the other is a spectrum of stable phases with homologous structures. In the metastable phase, Ge/Sb atoms and intrinsic vacancies occupy the Na sites; on the other hand, Te atoms are located at the Cl sites. These vacancies are produced by following γ/1+2γ to ensure the stoichiometry of the metastable pseudobinary compound. This metastable phase obstinately holds its NaCl-type structure and resists transformation to stable homologous structures, even at high temperatures on the GeTe-rich side of the system. In GeTe (γ=0), the NaCl-type atomic configuration itself is the stable structure. GeTe has, as is well known, a high-temperature cubic phase and a low-temperature rhombohedral phase. This GeTe and the pseudobinary compounds containing a small quantity of Sb2Te3 have their single-phase regions not on the GeTe–Sb2Te3 tie line but at Ge-poor sides off the line: in other words, the Na sites of these off-stoichiometric compounds have some excess vacancies besides the intrinsic vacancies. As Sb2Te3 is further added to GeTe, however, the structural transformation temperature continuously falls and the single-phase region converges on the tie line as the excess vacancies at the Na site disappear, which change its electrical property from metallic to semiconducting conductivity. The low-temperature rhombohedral phase is present up to near γ=0.14. The NaCl-type metastable phase becomes unstable with increased Sb2Te3; after subjecting the compound Ge8Sb2Te11 (γ=0.11) to heat treatment for 15 days at 773 K, a stable homologous structure appeared.

Epitaxial ferri(ferro)magnetic Fe3−xZnxO4 thin films (x=0–0.9) were prepared using a pulsed-laser deposition technique. The electrical conductivity and magnetic properties of Fe3−xZnxO4 thin film were systematically modulated for the entire range of Zn substitution. Anomalous Hall coefficient measurements revealed the presence of spin-polarized carriers at room temperature. Valence band spectra obtained by hard x-ray photoemission spectroscopy revealed that the density of states near the Fermi level was reduced with an increasing Zn concentration of x. These results indicate that this system will serve as a tunable ferromagnetic semiconductor with a strong electron correlation.