Inverse tunnel magnetoresistance in magnetic tunnel junctions with an Fe4N electrode

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 (V-B) 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 V-B dependence of TMR ratio were observed in the Fe4N/MgO/CoFeB-MTJ. The maximum TMR magnitude of 18.5% was obtained at V-B=-200 mV, where the current flows from Fe4N to CoFeB. The enhancement of the inverse TMR ratio around V-B=-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. (c) 2007 American Institute of Physics.