ALBERT

Notes: Using laser induced fluorescence detection of metastable H2(c 3Π−u, v=0–3, N=1–4) molecules in a beam at different distances from the source, the lifetime of resolved fine structure levels was determined. It was found to be much shorter for the F2 levels (∼150–10 μs for v=0–3, respectively) than for the F1 plus F3 components (several hundred to 70 μs). This is due to a forbidden (ΔN≠0) predissociation by the b 3Σ+u state, which operates preferentially on the F2 levels. Accurate bound–free Franck–Condon factor calculations reproduce the increasing trend of the predissociation rate in going from v=0–3. The absolute predissociation rates from previous theoretical work, however, can only be brought into agreement with the experimental results if they are multiplied with a common scale factor of 38.

Notes: The asymmetric wiggler, inserted since the end of 1990 on the Super-Aco storage ring in Orsay, has been built to produce a high rate and high flux of circularly polarized soft x rays in the 100–3000 eV range. This insertion device is particularly well suited to measure x-ray absorption spectra corresponding to dipole transitions towards electronic orbitals that are directly responsible for magnetism (3d states of first row transition metals, 4f states of rare earths). In this article we report the first magnetic circular x-ray dichroism spectra obtained with this insertion device. They exemplify the wide prospects of this experimental setup.

Notes: A new ac technique based on the nonlinear magnetic response of sintered YBaCuO material is introduced to determine quantitatively the zero-field-cooled and field-cooled remanent magnetization of this high Tc superconductor. It is demonstrated that by applying a dc-compensation field Hcomp, the signal of the second harmonic susceptibility of this material can be minimized. Comparison to the results obtained by dc-magnetization measurements (SQUID magnetometer) on identical samples show, that Hcomp is proportional to the corresponding dc remanence. Thus, Hcomp provides a measure to exploit this "memory'' effect of the second harmonic.

Notes: Theoretical calculations of the low lying excited states of the Zn atom and ZnH molecule are reported. An averaged relativistic effective core potential is used for the 1s2 2s2 2p4 3d10 electrons of Zn and the polarization and intrashell correlation effects are treated with a semiempirical core polarization potential. Spin–orbit splittings are incorporated into the correlated electronic states.

Notes: We attempt to establish the mathematical expression of the current and the magnetic field in a metallized capacitor. The expression of the impedance of this capacitor is also presented. The distribution of the current is discussed through the variation of the capacitor impedance and compared to experimental ones. There is good agreement between experimental and theoretical results. The analytical expressions of the magnetic field and the current also show a dependence on parameter δ2 akin to the skin depth in conductors. δ2 also depends on frequency. When δ2 is smaller than the outer radius of the capacitor, the current distribution becomes inhomogeneous.

Notes: Magnetic anisotropies of ultrathin transition-metal films are inherently related to their structural properties. In ultrathin films the large fraction of atoms located at the film interface generates strong interface anisotropies, whereas elastic strain fields caused by the forced registry of atoms at the substrate/film interface induce magnetoelastic anisotropy contributions. So far the experimental confirmation of the transition from these thin-film properties to bulk anisotropy properties, characterized by a dominating magnetocrystalline anisotropy, has not yet been presented. Magnetic anisotropies reflect, depending on their origin, both the crystallographic symmetry and the symmetry of the film geometry. For a clear separation between magnetoelastic, magnetocrystalline and Néel-type interface anisotropy contributions, the film symmetry and thickness must be chosen such that the respective different anisotropy contributions appear with different symmetries and film thickness dependencies. This is the case for (110)-oriented fcc Co films. In the present study we use the Brillouin light-scattering technique for the determination of the anisotropy contributions. An analysis of the spin-wave frequency measured as a function of the in-plane direction of the external field and the film thickness yields information about all relevant anisotropies. The samples used were molecular-beam-epitaxy grown in ultrahigh vacuum. Onto a Cu (110) single-crystal substrate a wedge-type sample and two staircase-shaped samples with distinct thicknesses in the range of 8–110 A(ring) were grown.To obtain symmetric Co/Cu interfaces the Co layers were covered with a 12 A(ring) Cu layer. Finally, a 25-A(ring)-thick Au protective layer was deposited. Low-energy electron-diffraction studies were used to obtain the structural data of the films. All relevant anisotropy contributions—the magnetocrystalline anisotropy, and the uniaxial in-plane and out-of-plane anisotropy contributions—were determined. Three different anisotropy regimes are observed as a function of the Co layer thickness dCo. This thickness regime up to 13 A(ring) is dominated by the magnetoelastic anisotropy contributions as a result of the pseudomorphic film growth of the Co layer. For Co layer thicknesses larger than 13 A(ring) we find a reduction of the magnetoelastic anisotropy contributions. This is structurally correlated to an anisotropic relaxation of the in-plane Co lattice constant. In the regime of dCo(approximately-greater-than)50 A(ring) we observe a thickness-independent value for the magnetocrystalline anisotropy contribution K1=−8.5×105 erg/cm3. This anisotropy contribution is largely suppressed for dCo〈50 A(ring). This finding might either indicate a breakdown of the usually postulated linear superposition principle of magnetic anisotropy contributions to the free anisotropy energy, or it might point to a subtle modification of the electronic band structure. At the onset of the magnetocrystalline anisotropy we find a change in the easy magnetization direction from 〈001〉 for thin Co films to 〈111〉 for thicker ones. For a more detailed discussion see Ref. .

Notes: The effect of substrates on the magnetic properties has been studied for Co and Fe films both on Al2O3 (112¯0) and MgO (001) substrates by using ferromagnetic resonance techniques. For Fe(001)/MgO(001) samples the thickness dependence of the magnetocrystalline constant and of the effective magnetization values have been determined from the in-plane angular variation of the resonance field H0. Different reasons for the thickness dependencies of these parameters are discussed. For Co(111)/Al2O3(112¯0) the angular variation of H0 exhibits an uniaxial anisotropy, for which several causes are discussed. For Co(112¯0)/MgO(100) a four-fold in-plane anisotropy was observed which is due to the twinned structure of these samples.

Notes: Low temperature photoluminescence (LTPL) measurements have been performed on 6H, 4H, and 15R polytype SiC crystals. In addition to well-known emission lines close to the band gap a couple of new features could be observed. Emission lines attributed to the recombination of bound excitons at aluminum acceptors have been seen in all three polytypes. A defect interpreted as a divacancy is described for SiC(4H). In SiC(6H) emission lines due to scandium centers have been observed. Furthermore the effect of a uniaxial stress on the LTPL spectrum is investigated.

Notes: It is shown that a recently proposed comment on our paper [J. Appl. Phys. 74, 291 (1993)] cannot be considered as a significant simplification by obtaining the deep level energy spectrum D(E).

Notes: The results of the transport and magnetization measurements on β-FeSi2 single crystals are presented. The magnetic field dependence of the Hall coefficient in n-type β-FeSi2 was observed in the temperature range of 30–300 K and explained in the limits of a two-band model. The magnetization measurements were performed within the range 4.2–300 K. It was shown that the contribution of the anomalous Hall effect to the total Hall voltage is negligible. Parameters of charge carriers, taking part in conductivity were calculated and the separation between the bands was estimated.