Characterization of interfacial properties in magnetic tunnel junctions by bias-dependent complex impedance spectroscopy

Intense research on magnetic tunnel junctions (MTJs), consisting of an insulating layer sandwiched by two magnetic layers, has been performed in recent years due to their possible applications on magnetic random access memory cells. The limitations on how MTJs can be used significantly depend on electronic transport process associated with metal/insulator interfaces. The large contrast in resistivities between magnetic and insulating layers causes accumulation of charge at interfaces when a bias is applied across the junction. The charge buildup at the interface leads to the deviation between measured capacitance and geometrical capacitance. Therefore, the measured capacitance of a MTJ is indicative of bulk and interfacial contributions. In this report, bias-dependent complex impedance spectroscopy has been utilized to investigate the interfacial effect.