Huge spin-polarization of L2(1)-ordered Co2MnSi epitaxial Heusler alloy film

Magnetic tunnel junctions (MTJs) with a stacking structure of epitaxial CO2MnSi/Al-O barrier/poly-crystalline CO75Fe25 were fabricated using an ultrahigh vacuum sputtering system. The epitaxial CO2MnSi bottom electrode exhibited highly ordered L2(1) structure and very smooth surface morphology. Observed magnetoresistance (MR) ratios of 70% at room temperature (RT) and 159% at 2 K are the highest values to date for MTJs using a Heusler alloy electrode. A high spin-polarization of 0.89 at 2 K for CO2MnSi obtained from Julliere's model coincided with the half-metallic band structure that was predicted by theoretical calculations.