Transport Properties of Low Resistance Underoxidized Magnetic Tunnel Junctions

Magnetic tunnel junctions (MTJs) are currently replacing spin valves as read sensors in high density media. To be implemented, MTJs must have low resistance-area product (RtimesA) and reasonable tunnel magnetoresistance (TMR) which are usually obtained using ultra-thin barriers. The use of thicker, underoxidized AlO_x barriers can also lead to similarly suitable MTJ-characteristics. Here we study the temperature dependence of the transport properties of 9 Aring underoxidized magnetic tunnel junctions, revealing the dominance of different transport mechanisms in different samples of the same wafer: tunnel, metallic or a mixture of the two, depending on MTJ-magnetic state. Such differences likely arise from slight structural differences inherent to the oxidation process. We further show that the MR-temperature dependence is stronger for MTJs displaying a metallic-like behavior (dR/dT>0) and compare such behavior with the enhanced MR(T) observed in current perpendicular to the plane (CPP) spin valves