Hans Steidl

Surface magnetic properties of oxygen on ferromagnetic films: a spin resolved MDS study

Using spin polarized metastable deexcitation spectroscopy (SPMDS) we determine spin asymmetries for remanently magnetized iron(110) and cobalt(0001) films clean and oxygen covered. For clean surfaces a dominance of minority spins is observed at the Fermi edge. At the Fermi edge oxygen exposure leads to a reversal of the dominance of the spin for iron, but not for cobalt, being in agreement with theoretical calculations. An oxygen induced structure at a kinetic energy of 5.5 eV shows a dominance of minority spins, but with different dependence on coverage for iron and cobalt.

Production of a spin-polarized, metastable He(23S) beam for studies in atomic and surface physics

This beam was developed as a target for a crossed-beam electron-atom scattering experiment on the interaction of a polarized spin-1/2 electron with a polarized spin-1 atom. In the future this beam will be used in “Spin-Polarized Metastable Atom Deexcitation Spectroscopy” (SPMDS) for studying ferromagnetic surfaces without and with adsorbate layers. We use a discharge source for producing a beam of metastable helium atoms, a permanent sextupole magnet with a central stop at its exit for selecting He(23S) atoms in the Zeeman substatems=+1, a zero-field spin flipper for reversing the atomic beam polarization with respect to a magnetic guiding field, and a Stern-Gerlach magnet for analyzing the atomic polarization. At a distance of 90 cm beyond the exit of the sextupole, in the “interaction region” of an experiment, the polarized beam has a circular cross section of about 6 mm FWHM and a particle density of 1 · 107 atoms/cm3. The reversible spin polarization was determined asP=0.90±0.02. A possible contamination of the beam with metastable singlet atoms is included within this value; the ground-state He atoms are not considered to be part of the polarized beam. An observed contamination with long-lived Rydberg atoms can easily be destroyed by applying a high electric field.

Surface magnetic properties of oxygen on Fe(110)

Abstract The magnetic properties of a chemisorbate on a ferromagnetic surface are investigated by means of spin polarized metastable deexcitation spectroscopy (SPMDS). The study was carried out with oxygen on magnetized Fe(110) films evaporated on W(110). By using a spin polarized He(2 3 S) beam, an intensity change is observed in the iron related structure near the Fermi edge when reversing the polarization of the incident He beam. This asymmetry changes its sign after oxygen exposure.

Surface magnetic properties of Fe(110) and Co(0001) films

Abstract The magnetic properties of ferromagnetic surfaces are investigated by means of spin-polarized metastable de-excitation spectroscopy (SPMDS). The study was carried out with thin magnetized Fe(110) and Co(0001) films grown epitaxially on W(110). By using a spin-polarized He(2 3 S) beam, different intensities in the structures near the Fermi edge could be observed when reversing the polarization of the incident He beam showing the dominance of the minority spin density in the surface—vacuum region.

Investigation of ferromagnetic surfaces with spin polarized metastable He(2 3S) atoms

Electron spectra of tungsten (110) and of thin cobalt (0001) films, clean and after oxygen exposure, have been taken using metastable de-excitation spectroscopy (MDS). The spectra of remanently magnetized Co(0001), obtained with spin polarized MDS (SPMDS), show different intensities in the cobalt induced structure when reversing the polarization of the incident spin polarized He(23S) atomic beam. Due to theextreme surface sensitivity and thespin selectivity of the de-excitation process, this is evidence of differences in thespin resolved density of states of theoutermost cobalt layer.

Interaction of spin-polarized helium 2(3)S-atoms with ferromagnetic surfaces

In recent years numerous investigations of clean and adsorbate covered substrates have been carried out by different methods. As most investigations of electronic properties use methods which give information averaged over a depth of a few atomic layers, below the surface, there is, in comparison not so much knowledge about the electronic properties at the surface. A distinct surface sensitivity, however, can be achieved by electron emission caused by impact of metastable He(23S)-atoms of thermal energy, a method called metastable deexcitation spectroscopy (MDS) (e.g. [1]). This technique probes predominantly the outermost atomic layer. The spin selective version of MDS uses an electron spin polarized He(23S) atomic beam (SPMDS) and was experimentally pioneered at Rice University [2]. Using the spin selectivity in the deexcitation process (at the surface), one has an excellent tool for. obtaining information on the magnetic properties of the outermost region of the surface. Here we report on studies of electron emission from clean and oxygen covered iron (110) and cobalt (0001) films. Due to the high intensity of our atomic beam we are able to carry out angle and energy resolving SPMDS measurements. With our spectrometer the energy distribution of the emitted electrons is determined directly.