Electronic structure and crystalline coherence in Fe/Si multilayers

Soft x-ray fluorescence spectroscopy has been used to examine the electronic structure of deeply buried silicide thin films that arise in Fe/Si multilayers. These systems exhibit antiferromagnetic (AF) coupling of the Fe layers, despite their lack of a noble metal spacer layer found in most GMR materials. Also, the degree of coupling is very dependent on preparation conditions, especially spacer layer thickness and growth temperature. The valence band spectra are quite different for films with different spacerlayer thickness, yet are very similar for films grown at different growth temperatures. This latter result is surprising since AF-coupling is strongly dependent on growth temperature. Combining near-edge x-ray absorption (NEXAFS) with the fluorescence data demonstrate that the local bonding structure in the silicide spacer layer in epitaxial films which exhibit AF-coupling are metallic. These results indicate the equal role of crystalline coherence and electronic structure in determining the magnetic properties of these systems.