J. Schoenes

Structure, magnetic, and magneto-optical properties of MnBi films grown on quartz and (001)GaAs substrates

MnBi films are prepared on quartz and on (001) orientated GaAs substrates by molecular beam epitaxy in ultrahigh vacuum environment. Both kinds of substrates are used simultaneously. The influence of the substrate material is investigated with respect to the structural, the magnetic, and magneto-optical properties of the MnBi films. By evaporating a 100 nm thick SiOx buffer layer the homogeneity of the composition is improved and a grain size of about 100 nm is achieved without adding other elements. In contrast to previous investigations, our measured magneto-optical Kerr rotation spectra show no Kerr rotation peak near 3.35 eV. These results confirm theoretical predictions whereupon this peak is attributed to oxygen which occupies interstitial sites in the regular MnBi lattice.

Large room‐temperature magneto‐optical Kerr effect in CuCr2Se4

The magneto‐optical polar Kerr effect has been measured on CuCr2Se4 single crystals between 0.55 and 5.0 eV. The single Kerr ellipticity eK reaches −1.19° at 0.96 eV which is (besides PtMnSb with θK=−1.27° at 1.72 eV) the highest value ever observed at room temperature. The figure of merit R1/2(θ2K + e2K)1/2 has a maximum value of 0.84° at 0.88 eV which is as high as in PtMnSb (0.83° at 1.57 eV). This large magneto‐optical Kerr effect is due to the steep plasma edge observed in the reflectivity R. First experiments show that the photon energy at which the plasma edge occurs can be shifted by suitable substitutions in CuCr2Se4.

Free-carrier compensation in ferromagnetic ion-implanted SnO2:Co

Magnetron sputtered SnO2 thin films on fused silica substrates were doped with 3, 5, and 7at.% Co by the ion-implantation technique leading to ferromagnetic order at room temperature. Transmission electron microscopy combined with energy loss spectroscopy confirms the absence of Co clusters which are larger than the resolution of ∼1nm. Electrical transport measurements using the Van der Pauw method show a high resistivity of the undoped SnO2 which increases with the Co concentration. The lower valence of Co with respect to Sn causes a compensation of donor electrons by localized holes.

Epitaxial yttrium growth mode on BaF2 (111) and CaF2 (111)

Abstract The molecular beam epitaxy of yttrium films on BaF2 (111) substrates has been studied. The surface morphology and the crystallinity of the yttrium films were investigated by reflection high energy electron diffraction. The growth of yttrium on BaF2 depends strongly on the surface modification of the substrate. For a substrate temperature of 200 °C, epitaxial films grow in the Stranski–Krastanov mode. However, for a BaF2 substrate temperature of 700 °C, which is the optimum growth temperature for the growth of yttrium on CaF2, only polycrystalline films are obtained. By optimizing the growth process, we succeeded growing yttrium films on BaF2 substrates having the same crystallinity as yttrium films grown on CaF2 substrates.

Structure and bonding in YHx as derived from elastic and inelastic light scattering

Abstract The optical properties in the visible and infrared (IR) as well as the Raman effect are reported for thin films of YH x with 2≤ x ≤ 3. From an analysis of the IR spectra, the Szigeti effective charges have been derived. It is found that in the insulating γ phase ( x ≈3) hydrogen is negatively charged with a transfer of about 0.5 e to every hydrogen atom. Raman scattering spectra display one line in YH 2 and up to 13 lines in YH 3 . A comparison with spectra of deuterated samples allows to identify hydrogen vibrations. An analysis of the polarization dependence evidences that the structure is non-centrosymmetric. The results support models for the electronic structure which assume strong electron correlations.

Noncentrosymmetric cubic helical ferromagnets Mn1 − yFeySi and Fe1 − xCoxSi

Two systems of noncentrosymmetric cubic helical magnets Mn1 − yFeySi (y = 0.06, 0.08, 0.10) and Fe1 − xCoxSi (x = 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.50) have been compared. The concentration dependences of the critical temperature and magnetic field have been obtained using small-angle polarized-neutron scattering and analyzed in the framework of the Bak-Jensen model. It has been established that, among the two interactions that play the main role in these systems, i.e., the isotropic symmetric ferromagnetic exchange and the Dzyaloshinskii-Moriya isotropic antisymmetric interaction, the former interaction determines the critical temperature in the Mn1 − yFeySi system and the latter interaction determines this temperature in the Fe1 − xCoxSi system.

Optical properties of DyP and DyBi: Experiment and theory

The near-normal incidence reflectivity of cleaved DyP and DyBi single crystals has been measured between 0.03 and 12 eV. Using the Kramers-Kronig relation, the optical conductivity, the dielectric function and the effective number of carriers contributing to optical transitions have been derived. Impressive agreement is obtained with spectra computed on the basis of a LMTO full-potential band-structure calculation within the local density approximation.

MO Kerr study of the 4f1 state

Abstract Recent measurements of the magneto-optical Kerr effect of the cerium monochalcogenides and monopnictides have brought a deeper insight into the character of the 4f 1 state. In these materials, the 4f → 5d transitions give rise to very sharp and larger Kerr rotation peaks. Among these, one finds the three largest ever measured Kerr rotation angles of 90°, 22.1° and 9.2° for cleaved single crystals of CeSb, CeS and CeBi, respectively. Furthermore, for the 4f 1 level, the effect of pf mixing has been found to be significant.

Interfacial reaction during the epitaxial growth of yttrium on CaF2(111)

By means of Auger electron spectroscopy and in situ reflection high-energy electron diffraction (RHEED) the interfacial reaction during the epitaxial growth of yttrium on CaF2(111) has been studied. The RHEED patterns confirm a smooth Volmer–Weber growth mode. Auger electron spectroscopy evidences a strong interdiffusion of the film and substrate, leading to a compressive in-plane strain of the growing film. Using RHEED, we can follow the strain relaxation via misfit glides during growth. The development and crystalline orientation of the glides are characterized.

Optical and magneto-optical properties of the cerium monochalcogenides

Abstract We report on measurements of the room temperature reflectivity between 0.03 and 12.4 eV and of the magneto-optical polar Kerr rotation in the energy range between 0.6 and 5.3 eV at 1.35 K in a magnetic field of 10 T on single crystals of CeSe. Although the magnetic moment amounts only to 0.376μB/Ce, a remarkable Kerr rotation τK of 5.5° has been measured at the photon energy of 2.6 eV. We assign this peak in θK to a 4f1 → 5d (EF) transition, enhanced by the low values of the optical constants in the plasma minimum of CeSe. A comparison with the magneto-optical spectrum of CeTe and with the optical spectra of CeS and CeTe is made.