Crystalline $\gamma$-Al$_2$O$_3$ barrier for magnetite-based Magnetic Tunnel Junctions

Magnetite Fe$_3$O$_4$ is an interesting material for spintronics because it is expected to exhibit a very high spin polarization at room temperature. In this framework, we have developed an Oxygen Plasma Assisted Molecular Beam Epitaxy setup well suited to the growth of Fe$_3$O$_4$/Al$_2$O$_3$ bilayers. We have successfully grown highly insulating, 1.5 to 2 nm-thick crystalline $\gamma$-Al$_2$O$_3$ layers free of pinholes. The Fe$_3$O$_4$ layer is unaffected by the deposition of the Al$_2$O$_3$ barrier as evidenced by thorough magnetic, chemical and structural characterizations. These breakthroughs pave the way to all-oxide Fe$_3$O$_4$/Al$_2$O$_3$/Fe$_3$O$_4$ fully epitaxial magnetic tunnel junctions.