Magnetic properties of bct FexMn1-x thin-film alloys investigated by linearly polarized soft-x-ray resonant magnetic reflectivity

The magnetic properties of FexMn1-x/Ir(001) superlattices (SL's) have been studied using linearly polarized soft x-ray resonant magnetic reflectivity (XRMS) at the Fe L-2,L-3 absorption edges. Previous superconducting quantum interference device magnetometry measurements have shown that the SL's exhibit a ferromagnetic behavior for x > 0.75 and a nonmagnetic or antiferromagnetic one for x < 0.75. XRMS measurements were performed on two SL's with compositions on each side of x = 0.75, as well as on a thin layer of Fe-rich alloy (x = 0.9). The Fe magnetic moments in these alloys were determined by comparing experimental and calculated energy-dependent asymmetry ratios at different angles in the reflectivity curves. Fe atoms are found in a high-spin ferromagnetic state for x = 0.9, while they are in a low-spin ferromagnetic stare for x = 0.7. Our results emphasize the role of the tetragonalization parameter c/a on the occurrence of the different magnetic states. Measurements, at the Mn L-2,L-3 edges in a bet Fe0.9Mn0.1 ultrathin layer reveal a net magnetic moment per Mn atom of about 1.7 mu(B) coupled antiparallel to the Fe one. [S0163-1829(99)03933-8].