C.F. van Bruggen

X-ray photoelectron spectra of 3d transition metal pyrites

Photoelectron spectra of the synthetic compounds FeS2, CoS2, NiS2, MnSe2, CoSe2, and NiSe2 and of a natural crystal of MnS2, all with the pyrite structure, are reported. The sulfur 3s and selenium 4s contributions are split into peaks for bonding and antibonding orbitals due to the covalent bonding in the molecular anion pairs. The difference in lineshape of the peaks for the bonding and antibonding orbitals is attributed to vibronic effects. The metal 2p32 spectra show the effects of multiplet splitting and satellites due to shake-up or shake-off processes. The valence band spectra consist of slightly overlapping contributions of anion p and metal 3d electrons. The metal 3d spectrum of FeS2 has a single strong peak of width 0.9 eV. The 3d spectra of the other compounds show structure due to several final state configurations.

Band-structure calculations, and magnetic and transport properties of ferromagnetic chromium tellurides (CrTe, Cr3Te4, Cr2Te3)

Electronic band-structure calculations are presented for the ferromagnetic compounds CrTe, Cr3Te4 and Cr2Te4 and Cr2Te3. In these compounds the Cr3d-Te5p covalency and the Cr3d(z2)-Cr3d(z2)-overlap along the c axis are the most important interactions. The magnetic polarisation of Te is parallel to the Cr local moment in CrTe, antiparallel to it in Cr2Te3 and about zero in Cr2Te4. Measurements of electronic transport properties (resistivity, Hall effect and thermo-electric power) and magnetic properties of Cr1- delta Te( delta =0.1) and Cr3+xTe4(x=0.2) indicate that these chromium tellurides are p-type metals, with strong interaction between the holes in the Te5p band and the Cr magnetic moments. In the literature the variation of the magnetic properties of Cr3.2Te4 near Ts approximately=100 K has been attributed to a change from a canted antiferromagnetic to a collinear ferromagnetic structure. However, our Hall-effect measurements indicate that the spin structure is not collinear ferromagnetic above Ts.

Half-metallic ferromagnets. II. Transport properties of NiMnSb and related inter-metallic compounds

For pt.I see ibid., vol.1, p.2341 (1989). The electrical resistivity and the Hall effect of inter-metallic compounds XMnSb (X=Pt, Ni, Au) and PtMnSn were investigated in the temperature region 4-1000 K. The results for the anomalous Hall effect were analysed in terms of skew scattering and side-jump contributions. This analysis is possible in a half-metallic ferromagnet because the conduction electron spin polarisation at T=0 K is known.

Half-metallic ferromagnets. I. Structure and magnetic properties of NiMnSb and related inter-metallic compounds

The authors present investigations of the crystal structure the microstructure and the magnetic properties of the inter-metallic compounds XMnSb (X=Pt, Ni, Co, Au, Cu) and PtMnSn. It was found that several of these materials contain precipitates of other phases and/or large atomic disorder, which can be influenced by heat treatment. The magnetic properties show an effective paramagnetic moment which differs from the value corresponding to the saturation moment at 0 K. This effect is attributed to a decrease of the conduction electron spin polarisation at high temperature.

Electronic band-structure calculations of some magnetic chromium compounds

Band-structure calculations of CrS, CrSe, Cr3Se4 and CrSb are presented. Together with the accompanying results for the chromium tellurides, these calculations give a coherent picture of the changes in the electronic structure caused by anion substitution and by introduction of cation vacancies. The importance of the Cr-X covalency and the 3d(z2)-3d(z2) overlap of Cr neighbours along the c axis is stressed. Further, the bandstructure calculations shed some light on the formation, the variation in magnitude and the coupling of the Cr magnetic moments and the indirect magnetic polarisation of the anion bands.

Electronic structure and magnetic, electrical and optical properties of ferromagnetic Heusler alloys

Abstract Measurements of the electrical resistivity and the Hall effect of the Heusler alloys NiMnSb, PtMnSb, CoMnSb, AuMnSb, CuMnSb and PtMnSn are reported. The anomalous Hall effect is analyzed in terms of the contributions from skew scattering and side jump. The spin polarization of the charge carriers is proportional to the magnetization. This is an indication that the electronic structure as a function of the temperature is best described by a local band model, with complete spin polarization of charge carriers parallel to the local magnetization at all temperatures. The spin disorder resistivity of NiMnSb is calculated with the local band model. The magneto-optical Kerr effect of PtMnSb is enhanced by the plasma resonance of the charge carriers.

THE ELECTRONIC-STRUCTURE OF SOME MONOVALENT-METAL INTERCALATES OF TIS2

The electronic structures of the layered compound TiS2 and its intercalates LiTiS2, NaTiS2 and AgTiS2 are calculated using the ASW method. Various deviations from the rigid-band model are observed, of which the increase of the Ti-3d/S-3p gap and the variation of the inter-sandwich and intra-sandwich interactions between S-3p orbitals are the most pronounced. The effect of the flattening of the TiS2 slabs-such as occurs at the 3R(I)-3R(II) transition in NaxTiS2 for x approximately=0.7-on the electronic structure is calculated for Na1TiS2 and is shown to be coupled with an increased ionicity in the Ti-S bond.

Magnetic properties of MnxMg1-xS solid solutions

Abstract The static magnetic properties of the polycrystalline solid solutions Mn x Mg 1- x S(0 x ⩽1) are reported. The experimental data reveal the appearance of a critical concentration x c =0.13±0.01 for long-range magnetic ordering, which is in good agreement with the result of a series expansion of the mean cluster size for a face-centered cubic lattice with exchange interactions up to 12 nearest neighbours and 6 next-nearest neighbours. At concentrations far below x c the existence of long-range exchange interactions is demonstrated.

Semiconducting and magnetic properties of rhombohedral Cr2S3

Abstract Measurements of the magnetic properties and the electrical resistivity, the Hall effect, the thermoelectric power, and the magnetoresistance were carried out on polycrystalline rhombohedral Cr2S3. The electrical transport properties show an anomalous behaviour near the Curie temperature TC = 120°K. These anomalies are ascribed to the interaction between charge carriers and localized magnetic moments, leading to an exchange splitting of the conduction band and to spin-disorder scattering of the charge carriers.

Photoelectron spectra of 2H-TaS2 and SnxTaS2

Photoelectron spectra of Sn1/3TaS2 and SnTaS2 are reported and compared with spectra of 2H-TaS2 and SnS. It is possible to trace the charge transfer from Sn to Ta from the observed increase of the occupation of the lowest Ta 5d band and from the observed decrease of the positive charge on Ta. The charge transfer is the same in Sn1/3TaS2 as in SnTaS2. The data indicate the presence of two types of Sn atoms in SnTaS2. The Ta 4f peaks show an asymmetric broadening; and an anomalous intensity ratio of the 4f7 and 4f5/2 peaks. These effects are ascribed to shake-up effects involving excitations of 5d electrons. The average relaxation energy of a Ta 4f hole is found to be 1.1 eV.