Highly Spin-Polarized Tunneling in Fully Epitaxial Magnetic Tunnel Junctions Using Full-Heusler Alloy Co$_2$Cr$_0.6$Fe$_0.4$Al Thin Film and MgO Tunnel Barrier

Highly spin-polarized tunneling with tunnel magnetoresistance (TMR) ratios of 90% at room temperature and 240% at 4.2 K was demonstrated for fully epitaxial magnetic tunnel junctions fabricated using a cobalt-based full-Heusler alloy Co
₂
Cr
_0.6
Fe
_0.4
Al (CCFA) thin film having a composition close to the stoichiometric one and a MgO tunnel barrier. A high tunneling spin polarization of 0.79 at 4.2 K was obtained for the epitaxial CCFA films from the TMR ratios. This adds to the promise of the fully epitaxial MTJ as a key device structure for utilizing the intrinsically high spin polarizations of Co-based full-Heusler alloy thin films