Huge Spin-Polarization of L21-Ordered Co2MnSi Epitaxial Heusler Alloy Film

Abstract

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 L2₁ 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.