Origin of induced Sn magnetic moments in thin Fe/Cr/Sn/Cr multilayers

Abstract

The origin of magnetic moment induced on one monolayer of Sn embedded within thin layers of Cr in Fe/Cr/Sn/Cr and Cr/Sn multilayers is investigated by first-principle spin-polarized electronic structure calculation. The structures consist of 1.15 nm (8 monolayers) and 1.3 nm (9 monolayers) of Fe, and 0.86 nm (6 monolayers) to 2.4 nm (17 monolayers) of Cr. The position of the Sn monolayer in Cr is either symmetric or asymmetric with respect to the Fe layers. It is found that in all these multilayers the Sn atoms get a small magnetic moment which is predominantly $5d$ in character. This is induced by the exchange interaction with the $3d\ensuremath{-}\mathrm{Cr}$ orbitals at the Cr/Sn interfaces. We find that the presence of Fe layers reduces the magnetic moment of Cr atom at the Cr/Sn interface, and therefore the induced magnetic moment on Sn atom decreased from $0.067{\ensuremath{\mu}}_{B}/\mathrm{atom}$ in Cr/Sn structure to $0.044{\ensuremath{\mu}}_{B}/\mathrm{atom}$ in Fe/Cr/Sn/Cr structure. These predictions are in strong correlation with M\ossbauer observations at the ${}^{119}\mathrm{Sn}$ site: the measured hyperfine field which in turn is affected by magnetic moment of surrounding Cr atoms, decreases from 13 T for Cr/Sn to 2 T for Fe/Cr/Sn/Cr multilayers. It is also found that the magnetic moment of a Cr atom depends strongly on its distance from the Fe layer, and therefore the induced magnetic moment of Sn is also influenced by the thickness of Cr multilayers. Our results show that the magnetic moments on Cr sites decrease smoothly away from the Fe layer and then increase abruptly at the Cr/Sn interface.