Influence of ferromagnetic substrate on the magnetoresistance of Cr film across a nonmagnetic insulating layer

Abstract

(5 nm) Cr/(x?nm) MgO/Mn0.52Zn0.48Fe2O4 (MnZn spinel) substrate (1<x<7?nm), as well as (5 nm) Cr/(7 nm) MgO/glass substrate structures have been grown using molecular beam epitaxy. The influence of the MnZn spinel on the in-plane transport and magnetotransport properties of the Cr layer were studied. The existence of pinholes in the MgO layer was explored by evaluating resistance versus temperature, R(T), dependencies. A hump was observed on the R(T) curves for the MgO layer thickness (tMgO) less than 5 nm. This results from the electrical coupling between the Cr film and the MnZn spinel substrate through the pinholes in the MgO layer. A reversal of the magnetoresistance (MR) sign in Cr film was observed when tMgO is less than 7 nm. It is thought that the effect of the electrical coupling through the pinholes and the magnetostatic coupling are not the reasons for the observed negative MR. A model is proposed which suggests that the magnetic structure in the Cr film adjoining a pinhole is distorted because of the exchange coupling. Such areas in the Cr film are thought to contribute to the negative MR.