The magnetic map of FeMn alloy thin films on Co(0 0 1) and Co/FeMn/Co(0 0 1) trilayers

Recent X-ray magnetic circular dichroism and magneto-optical Kerr effect performed by Matthes et al. [J. Appl. Phys. 93 (2003) 6504] on in situ layered systems of fcc Co and FeMn epitaxially grown onto Cu(0 0 1) templates as well as Co/FeMn/Co trilayers display very interesting results. Measurements showed that the magnetic moment on Fe is parallel to the Co magnetization direction whereas, for Mn the XMCD signals are small. In order to explain this behavior ab initio density functional calculations on (Fe0.5Mn0.5)n/Co(0 0 1) and Co/(Fe0.5Mn0.5)n/Co(0 0 1) have been performed for n varying from 1 to 3. Within generalized gradient corrections the Fe–Mn interfacial alloy, one monolayer thick on Co(0 0 1), with ferromagnetic coupling between Fe and Mn corresponds to the ground state whereas the same Fe–Mn monolayer in Co/FeMn/Co presents a magnetic moment of Mn opposite to that of Fe and Co. For all systems investigated we obtain a ferromagnetic polarization between Fe and Co atoms in agreement with the XMCD results. The behavior of the Mn polarization is more complex: an antiferromagnetic polarization between Mn atoms in nearest neighboring FeMn alloy plane is always obtained.