Giant Tunnel Magnetoresistance at Room Temperature for Junctions using Full-Heusler Co₂FeAl_0.5Si_0.5 Electrodes

Abstract

The authors have investigated the tunnel magnetoresistance (TMR) effect of magnetic tunnel junctions (MTJs) with Co2FeAl0.5Si0.5 full-Heusler electrodes and a MgO barrier in the thickness range of 1.5–2.5 nm. A cross-sectional transmission electron micrograph showed the epitaxial growth of both the upper and lower Co2FeAl0.5Si0.5 layers and a MgO barrier and some distortion in the MgO barrier after annealing above 400 °C. An exponential dependence of resistance × area product on MgO barrier thickness was observed. TMR ratio was strongly affected by MgO barrier thickness, exhibiting maxima of 220% at room temperature and 390% at 5 K. The latter corresponds to the spin polarization of 0.81. It was also found that the features of this MTJ include a small asymmetry voltage and weak temperature dependence of its TMR ratio.