F. Passek

Spin-dependent electron attenuation lengths and influence on spectroscopic data

Abstract Inverse photoemission from W(110) becomes spin dependent when the surface is covered with ultrathin ferromagnetic iron films. The spin asymmetry is not intrinsic to the tungsten electronic structure but is caused by spin-dependent electron attenuation within the ferromagnetic overlayer. The ratio of 1.7 ± 0.3 between the spin-down and spin-up attenuation lengths for an electron energy of 12.6 eV above the Fermi level can be explained within a simple model by inelastic scattering. The influence of spin-dependent attenuation lengths on experimental data from electron spectroscopy is discussed and demonstrated by simulations. The observed electron spin polarization or spin asymmetry is strongly affected, while the energetic positions of features in spin-up and spin-down spectra are not.

Magnetic phases of fcc-like Fe films on Cu(001): Answers from the spin-dependent electronic structure

Abstract The empty electronic structure of room temperature-grown fcc-like Fe films on Cu(001) is studied by spin-resolved inverse photoemission. For 6 monolayers, the magnetic exchange splitting of 0.9 eV of an sp -like surface state proves ferromagnetic order of the surface layer. The spin dependence of bulk-like states and the response to adsorbates reveal more than one, yet metastable ferromagnetic surface layers on top of nonferromagnetic layers. No indication of antiferromagnetic interlayer coupling was found at 90 K. Thinner films of 2.5 monolayers are completely in a stable ferromagnetic state with enhanced exchange splitting of the d states.

High-performance x-ray detector for appearance potential spectroscopy

A high-performance detector for soft x-ray appearance potential spectroscopy is described. It basically consists of an alkali halide photon-to-electron converting layer evaporated onto a self-supporting amorphous carbon foil. This combination absorbs the low energy photons thereby increasing the signal-to-noise ratio. Further improvement of the signal-to-noise ratio is achieved by an additional x-ray filter. The choice of filter and converter material depends on the characteristic radiation of interest. The electrons emitted from the converter are detected by means of a microchannel plate. With this detector a signal-to-noise ratio of 150 was obtained at the diamond appearance potential spectroscopic peak for 5 mC charge per point.

Temperature-dependent surface magnetization of FeNi3(111) studied by spin-resolved appearance potential spectroscopy

The temperature-dependent magnetic properties of the surface were investigated by means of spin-resolved appearance potential spectroscopy. Within the temperature range studied, from 100 K to 1100 K, two phase transitions occur in the bulk: a compositional order-disorder phase transition between 770 and 785 K and a ferromagnetic-paramagnetic phase transition with a Curie temperature of 863 K. The first one does not show up in the appearance potential signals of Fe and Ni, while the latter is reflected in the spin-asymmetry signals. Both the Fe and the Ni signals follow the bulk magnetization curve of with no evidence of any exceptional surface magnetic properties. Furthermore, our data show that, to a good approximation, the spin asymmetry of the appearance potential signal is proportional to the magnetization.