Magnetic properties of epitaxial Fe${}_3$O${}_4$ films with various crystal orientations and TMR effect in room temperature

Abstract

Fe${}_3$O${}_4$ is a ferrimagnetic spinel ferrite that exhibits electric conductivity at room temperature (RT). Although the material has been predicted to be a half metal according to ab-initio calculations, magnetic tunnel junctions (MTJs) with Fe${}_3$O${}_4$ electrodes have demonstrated a small tunnel magnetoresistance effect. Not even the sign of the TMR ratio has been experimentally established. Here, we report on the magnetic properties of epitaxial Fe${}_3$O${}_4$ films with various crystal orientations. The films exhibited apparent crystal orientation dependence on hysteresis curves. In particular, Fe${}_3$O${}_4$(110) films exhibited in-plane uniaxial magnetic anisotropy. With respect to the squareness of hysteresis, Fe${}_3$O${}_4$ (111) demonstrated the largest squareness. Furthermore, we fabricated MTJs with Fe${}_3$O${}_4$(110) electrodes, and obtained an TMR effect of -12\% at RT. The negative TMR ratio corresponded to the negative spin polarization of Fe${}_3$O${}_4$ predicted from band calculations.

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