Room-temperature spin filtering in a CoFe₂O₄∕MgAl₂O₄∕Fe₃O₄ magnetic tunnel barrier

By growing ultrathin and high quality CoFe₂O₄∕MgAl₂O₄∕Fe₃O₄ epitaxial multilayers, we have demonstrated a room temperature spin filter junction, which could open the way for highly polarized spin injection, single-qubit spintronic measurements, magnetic field sensing, and other applications. In these devices the Fe₃O₄ layer functions as a source of spin polarized electrons while the CoFe₂O₄∕MgAl₂O₄ double barrier functions as a spin filter. The current-voltage curves depend on the relative orientation of the magnetization of the Fe₃O₄ and CoFe₂O₄ layers and display a large magnetoresistive effect. The inferred net spin polarizations produced by the junctions typically exceeded 70%.