Band-folding-driven high tunnel magnetoresistance ratios in (111)-oriented junctions with SrTiO${}_3$ barriers

Abstract

We theoretically study the tunnel magnetoresistance (TMR) effect in (111)-oriented magnetic tunnel junctions (MTJs) with SrTiO${}_3$ barriers, Co/SrTiO${}_3$/Co(111) and Ni/SrTiO${}_3$/Ni(111). Our analysis combining the first-principles calculation and the Landauer formula shows that the Co-based MTJ has a high TMR ratio over 500%, while the Ni-based MTJ has a smaller value (290%). Since the in-plane lattice periodicity of SrTiO${}_3$ is about twice that of the primitive cell of fcc Co (Ni), the original bands of Co (Ni) are folded in the $k_x$-$k_y$ plane corresponding to the $ab$ plane of the MTJ supercell. We find that this band folding gives a half-metallic band structure in the ${\Lambda }_1$ state of Co (Ni) and the coherent tunneling of such a half-metallic ${\Lambda }_1$ state yields a high TMR ratio. We also reveal that the difference in the TMR ratio between the Co- and Ni-based MTJs can be understood by different $s$-orbital weights in the ${\Lambda }_1$ band at the Fermi level.

7 pages, 5 figures, 3 tables

References in corpus (3)

• Interface-driven giant tunnel magnetoresistance in (111)-oriented junctions
• Crucial role of interfacial $s$-$d$ exchange interaction in the temperature dependence of tunnel magnetoresistance
• First-principles study on magnetic tunneling junctions with semiconducting CuInSe${}_2$ and CuGaSe${}_2$ barriers