Ch. Roth

Antiferromagnetic Coupling of a Cr Overlayer to Fe(100)

The magnetic moment of Cr overlayers deposited on Fe(100) was investigated by spin-resolved core level photoemission. Data for the Cr 3p level show that a monolayer of Cr is ferromagnetically ordered with a magnetic moment oriented antiparallel to the Fe moments. The results suggest that at room temperature the moment of a Cr monolayer on Fe is of the order of 0.5 to 1μB per Cr atom.

Magnetic linear dichroism in soft X-ray core level photoemission from iron

Abstract We have observed magnetic linear dichroism in soft x-ray core-level photo-emission from ferromagnets: With linearly polarized light, the Fe 3p lineshape depends strongly on the relative orientation of the light electric field vector E and the magnetization vector M . For s-polarized light and collinear orientation of E and M the core level line shows a single peak. With E ⊥ M a double-peaked line is observed. We attribute this change to the MLD effect as predicted recently 1 .

Spin-polarized electron spectroscopy as a combined chemical and magnetic probe

Abstract Photoelectron spectra of inner core states of magnetic material show polarization features determined by the magnetic properties of the valence electrons. This offers a new possibilty of using electron spectroscopy as a magnetic probe. The low intensity of these photoemission lines led us to use very-low-energy-electron-scattering from Fe as spinpolarimeter with an efficiency about 20 times higher than previously used spin detection techniques. First experiments on the Fe 3p and 3s core levels confirm exchange split lines. For thin Cr overlayers on Fe(001) we find the polarization of the Cr 3p level for Cr coverages up to two monolayers to be opposite to that of the Fe 3p core level. Effects of the film thickness on the spin-resolved core level spectra are discussed.

Linear magnetic dichroism in photoemission

Results for the linear magnetic dichroism of Fe 2p spin-resolved photoemission with high energy resolution are reported. The results are qualitatively similar to those for the 3p level, with the advantage that the fine structure split sublevels (j = 1/2 and j = 3/2) are well separated, facilitating comparison with theoretical models. The finite dichroism in the energy region between the two photoemission peaks is not caused by secondaries, but appears to be a nontrivial effect. The 3p dichroism depends on photon energy: it is maximum at 140 eV, and vanishes around 300 eV photon energy.

Magnetic linear dichroism in angle-resolved valence band photoemission from Fe(001)

Abstract We report the observation of magnetic linear dichroism in angle resolved valence band photoemission from Fe(001), manifesting itself in a change of the spectrum upon reversal of the magnetization direction.

A new magnetic linear dichroism in photoabsorption at the Fe M2,3 edge

Abstract We have found a new type of magnetic linear dichroism in photoabsorption spectra at the Fe M 2,3 edge. The spectra excited by p-polarized light at oblique incidence show dichroism when the magnetization direction changes from parallel to antiparallel to n × q , where n is a vector perpendicular to the sample surface and q is the photon momentum. The dichroism is enhanced when the light impinges on the sample towards grazing incidence.

INFLUENCE OF PHOTOELECTRON DIFFRACTION ON MAGNETIC LINEAR DICHROISM

We studied the influence of photoelectron diffraction on magnetic linear dichroism and spin polarization in Co and Fe 3p photoemission excited by linearly polarized synchrotron radiation. We find a strong variation of the magnetic linear dichroism with emission direction. The spin polarization related to the spin–orbit interaction varies in a similar manner. This angular variation closely tracks that of the magnetic dichroism. In contrast, the exchange-induced spin polarization (-12+2)% does not vary appreciably with emission angle. These findings suggest that the main cause for the observed effects is the angular momentum character of the photoelectron wave.

Element-specific magnetic domain imaging based on linear and circular magnetic dichroism in photoabsorption

The discovery of magnetic dichroism in core level spectroscopy opened the route to magnetic domain imaging. By employing light in the soft X-ray regime one obtains chemically specific information. Besides the commonly used circular magnetic dichroism (MCD), we demonstrate feasibility of using linear magnetic dichroism in absorption for domain imaging in the photo electron emission microscope (PEEM). By combining different light polarizations, one obtains vectorial information on the magnetic moment distribution close to the surrface.

DIFFRACTION OF SPIN-POLARIZED Cu 3p PHOTOELECTRONS

We measured the spin–orbit-induced spin polarization in Cu 3p photoemission for fixed angle between light incidence and electron collection, while varying the emission angle relative to the crystal lattice. The polarization is found to vary strongly with emission direction in both sublevels. However, the ratio between the polarizations of the j=3/2 and j=1/2 sublevels is close to -1/2 for all emission directions. The spin polarization and its dependence on emission direction can both be viewed as arising from the angular momentum character of the final state wave which is imposed by the excitation conditions.

Spin-Resolved Core Level Photoemission Spectroscopy

Core level photoelectron spectroscopy has been used extensively during the past decades not only with the aim of understanding the fundamental effects governing the spectra, but also for its possibilities of helping to solve more technical materials’ problems. These aspects are covered by various lectures within this summer school. The analytical capabilities are based on analyzing changes of intensity, binding energy, lineshape, and occurence of satellites in core level photoemission spectra in terms of composition, chemical state of constituents, and local electronic structure.