Inverse tunnel magnetoresistance in magnetic tunnel junctions with an Fe4N electrode

Abstract

The magnetotransport properties of Fe4N∕MgO∕CoFeB and Fe/MgO/CoFeB magnetic tunnel junctions (MTJs) were investigated at room temperature. In the Fe/MgO/CoFeB-MTJ, normal tunnel magnetoresistance (TMR) effect and roughly symmetric bias voltage (VB) dependence were observed, similar to the MTJs exhibiting coherent tunneling such as Fe/MgO/Fe. On the other hand, the inverse TMR effect, showing higher tunnel resistance for parallel magnetization configuration than for antiparallel configuration, and strong asymmetric VB dependence of TMR ratio were observed in the Fe4N∕MgO∕CoFeB-MTJ. The maximum TMR magnitude of 18.5% was obtained at VB=−200 mV, where the current flows from Fe4N to CoFeB. The enhancement of the inverse TMR ratio around VB=−200 mV is due to the broad peak of tunnel conductance in antiparallel configuration of Fe4N and CoFeB magnetizations. A large peak of the density of state at +300 meV from the Fermi level for minority spin electrons of bulk Fe4N might be an origin of this phenomenon.