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

TL;DR

This study investigates the magnetic properties of epitaxial Fe$_3$O$_4$ films with different crystal orientations and reports a room-temperature TMR effect of -12% in Fe$_3$O$_4$(110) based magnetic tunnel junctions, aligning with theoretical predictions.

Contribution

It provides new experimental insights into the orientation-dependent magnetic properties and TMR effects of Fe$_3$O$_4$ films at room temperature.

Findings

Fe$_3$O$_4$ films show orientation-dependent hysteresis behavior.

Fe$_3$O$_4$(110) exhibits in-plane uniaxial magnetic anisotropy.

MTJs with Fe$_3$O$_4$(110) show a -12% TMR effect at 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.