H. Hopster

Magnetization reversal properties near the reorientation phase transition of ultrathin Fe/Ag(100) films

We have measured the magnetization reversal properties of ultrathin Fe/Ag(100) films in the vicinity of the reorientation phase transition using the magneto‐optical Kerr effect. Near the reorientation temperature Tr, we observe a characteristic change in the perpendicular magnetization curves M(H) from a strongly nonlinear behavior for T<Tr to a simple linear field dependence above Tr. The experimental observations are discussed within the context of the expected temperature‐dependent magnetization structure and the corresponding magnetization reversal processes.

Magnetic reorientation transition in epitaxial Gd-films

Abstract The susceptibility of epitaxial Gd/W(110)-films was investigated as a function of temperature and film thickness, using a magnetooptical measurement technique. In addition to the sharp peak at the Curie temperature T C , a second peak below T C was observed for film thicknesses d ≥ 35 nm. This peak shifts to lower temperatures with increasing film thickness. The origin of this second susceptibility maxinum has been identified as a reorientation transition of the magnetization. Results from micromagnetic calculations using bulk gadolinium parameters are fully consistent with the observed behavior.

Spin‐dependent elastic and inelastic electron scattering from magnetic surfaces (invited)

Results from scattering experiments, using a polarized electron beam combined with polarization analysis, are presented and discussed. There is no evidence of depolarization in quasielastic scattering for the systems studied [Ni(110), Ni(110)O(2×1), paramagnetic Ni(110), Pt(111), graphite]. In inelastic scattering from graphite for small energy losses the depolarization is found to be weak, whereas for ferromagnetic Fe and Ni surfaces large spin‐flip contributions have been reported for small energy losses.

SPIN DEPENDENT MEAN-FREE PATH OF LOW-ENERGY ELECTRONS IN FERROMAGNETIC MATERIALS

Abstract Spin resolved attenuation measurements of electrons transmitted through overlayers of Fe and Co show that the electron inelastic mean free path (IMFP) in these materials is spin-dependent at low energies. The spin-up IMFP is larger than the spin-down IMFP. The values from different studies are in reasonable agreement. The data suggest that the origin of the spin dependence is mainly due to inelastic processes. Effects from spin dependent elastic scattering have not been identified directly in these experiments. The spin filter effect based on preferential attenuation of spin-down electrons can be used as a basis of spin polarization detectors.

Spin-poiarized EELS of surfaces

Abstract The spin dependence of electron energy loss processes in Ni is studied in detail by spin polarized electron energy loss spectroscopy (SPEELS). Exchange scattering plays a dominant role for small energy losses with a large contribution due to Stoner excitations. The angle and energy dependence of spin asymmetries can be described by the superposition of nearly isotropic impact scattering and largely spin independent dipole losses, strongly peaked around specular. The absence of a significant temperature dependence in the spin asymmetry spectrum is consistent with the persistence of local magnetic moments and a spin-split electronic structure at (and above) T C . It is suggested that the observed spin asymmetries give rise to a spin-dependent electron mean-free-path at low energies and play a role in the spin polarization enhancement and the surface sensitivity of low-energy secondary electrons.