Magnetic dead layer at the interface between a Co film and the topological insulator Bi2Se3

Abstract

Co films were grown on top of a topological insulator Bi${}_{2}$Se${}_{3}$(111) substrate and studied using magneto-optic Kerr effect (MOKE) and x-ray magnetic circular dichroism (XMCD). Both MOKE and XMCD results show that there exists a \ensuremath{\sim}1.2-nm-thick magnetic dead layer of the Co film; i.e., an \ensuremath{\sim}1.2-nm Co film at the Co/Bi${}_{2}$Se${}_{3}$(111) interface loses its ferromagnetic order. The Co ferromagnetic order can be completely resumed by inserting a 3-nm Ag layer between the Co and Bi${}_{2}$Se${}_{3}$, indicating that the magnetic dead layer is due to the Co/Bi${}_{2}$Se${}_{3}$ interfacial mixing which is supported by the Co $L$-edge spectroscopy results.