Epitaxial Growth of Co<sub>0.75</sub>Fe<sub>2.25</sub>O<sub>4</sub>/NiO Bilayer on MgO(001) Substrate

Abstract

Co x Fe 3−x O 4 (CFO) films epitaxially grown on MgO(001) substrates show perpendicular magnetic anisotropy as high as 10 Merg/cm3[1]. However, magnetization is dependent on thickness. The magnetization per unit area linearly increases with increasing thickness of the films. Although the slope corresponds to the bulk magnetization, the slope intersects the horizontal (thickness) axis, suggesting that a magnetic dead layer exists at the interface/surface of the films. There are several possible reasons for the decrease in magnetization at the interface such as diffusion of Mg from the substrates, existence of anti-phase boundaries (APBs), and so on. In order to prevent the formation of the dead layer and improve the magnetic properties at the interface, we investigated the effect of a NiO insertion layer on the magnetization of CFO films. It has been reported that the insertion layer of NiO prevents Mg diffusion from MgO substrates in Fe 3 O 4 /MgO(001)[2]. Since NiO is isostructural with MgO, we can expect that APBs in CFO films are formed on the NiO insertion layers as well as on the MgO surfaces.