Magnetic tunnel junctions using B2-ordered Co2MnAl Heusler alloy epitaxial electrode

Abstract

Magnetic tunnel junctions were fabricated with epitaxially grown ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Al}$ bottom electrodes combined with an Al–O tunnel barrier using a magnetron sputtering system. The epitaxial ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Al}$ electrode had very low surface roughness of $0.2\mathrm{nm}$ and a highly ordered $B2$ structure. Magnetic tunnel junctions (MTJs) with a stacking structure of epitaxial-${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Al}∕\mathrm{Al}–\mathrm{O}∕\mathrm{Co}\mathrm{Fe}∕\mathrm{Ir}\mathrm{Mn}$ exhibited large tunnel magnetoresistance (TMR) ratios of 65% at room temperature and 83% at $10\mathrm{K}$ . The TMR ratios were larger than those of a MTJ with a ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Al}$ polycrystalline electrode.