Tunneling processes in thin MgO magnetic junctions

Abstract

Magnetic tunnel junctions (MTJs) with MgO barriers are used in a variety of applications, from read heads to novel microwave devices. In this work, we probed the temperature (T) dependence of the electrical transport of sputtered CoFeB/MgO/CoFeB MTJs with different barrier thicknesses (tb=0.75–1.35 nm). We show evidence that spin-polarized direct elastic tunneling is the dominant mechanism determining the T-dependence of the tunnel conductance (G) and magnetoresistance for tb≥0.85 nm. Also, the electronic thermal smearing near the Fermi level plays a key role in G(T). We observe the onset of pinholes for MTJs with 0.75 nm of MgO, with a transition to metallic-like transport.