Spin filtering through ferrimagnetic NiFe2O4 tunnel barriers

We report experiments of spin-filtering through ultrathin insulating layers of the high Curie temperature ferrimagnetic oxide NiFe2O4 (NFO). The spin-filtering efficiency of electrons tunneling from a gold electrode through NFO is analyzed with a counter-electrode of La2/3Sr1/3MnO3 (LSMO). We measure a tunnel magnetoresistance of 40%-50% when the configuration of the magnetizations of the NFO and LSMO goes from parallel to antiparallel. This value corresponds to a spin-filtering efficiency of up to 22% by the NFO barrier. We discuss the sign and temperature dependence of the spin-filter effect and argue that our results show the potential of spinel ferrites for spin-filtering and injection. (c) 2006 American Institute of Physics.