Role of interfacial roughness on bias-dependent magnetoresistance and transport properties in magnetic tunnel junctions

The effects of metal-insulator interfacial roughness, modulated by Ar + irradiation, on bias dependence of tunnel magnetoresistance (TMR) and electrical transport of Co Fe - Al O x - Co Fe magnetic tunnel junctions (MTJs) have been studied. Reduction of TMR ratio and asymmetric TMR falloff curves as a function of dc bias have been observed for Ar + -irradiated MTJs. The results are analyzed by x-ray reflectivity together with complex impedance techniques, indicating interfacial roughness which likely results in a proportional rising trap state density (TSD). Increasing TSD for Ar + -irradiated MTJs increases an unpolarized current which decreases TMR ratio. The asymmetric TMR falloff curves are attributed to the different TSDs of bottom and top Co Fe - Al O x interfaces in tunneling process.