Influence of growth parameters on the spin-filtering properties of epitaxial ferrite tunnel barriers

In spintronics, spin-filtering is a physical phenomenon which has the potential to produce highly spin-polarized currents by the spin-selective transport of electrons across a ferromagnetic tunnel barrier. The insulating ferrites MnFe$_{2}$O$_{4}$, CoFe$_{2}$O$_{4}$ and NiFe$_{2}$O$_{4}$, whose Curie temperatures are above 300K, are promising candidates for spin-filtering at room temperature. In this work, we report on the in-depth study of structural, chemical and physical properties of epitaxial ferrite ultra-thin films and associated spin-filtering measurements as a function of different growth parameters. We analyze the effect of oxidation on the physical properties and the resultant spin-polarization. The influence of structural defects on the spin-filter efficiency is also put on view by tunneling magnetoresistance. Finally, we show the impact of the MgAl$_{2}$O$_{4}$(001) substrates on the magnetic behavior of cobalt ferrite tunnel barriers revealing the important role played by strains in the spin-filter properties.