Anisotropy of the L_2,3 x-ray magnetic linear dichroism of Fe films on GaAs: Experiment and ab initio theory

We report investigations of the anisotropy of the x-ray magnetic linear dichroism (XMLD) of thin single-crystalline Fe films on GaAs substrates with film thicknesses of 3 nm and 7 nm, respectively. The orientation of the in-plane Fe magnetization with respect to the crystal axes is stepwise rotated from the [1 1 0] to the [0 1 0] direction and the Fe L_2,3 XMLD spectrum is measured at every orientation step. A highly anisotropic XMLD signal at the Fe L₂ and L₃ edges is observed, which origin is analyzed in detail. We show that the measured anisotropic XMLD spectra are in reasonable agreement with ab initio calculated spectra. The XMLD anisotropy is shown to be a consequence of the cubic crystal-field split density of 3d states, which are selectively probed by transitions from the spin-orbit and exchange-split 2p core levels. We furthermore investigate computationally the influences of the spin-orbit interaction of the Fe3d valence electrons as well as of stress in the Fe films. The Fe3d spin-orbit interaction only leads to small modifications of the XMLD spectra, whereas tetragonal deformation of the films can cause a larger modification of the spectra.