Andreev reflection in ferrimagnetic CoFe2O4 spin filters

We have performed point-contact spectroscopy measurements on a sample constituted by a metallic ferromagnetic oxide (SrRuO3) bottom electrode and a tunnel ferrimagnetic (CoFe2O4) barrier. Andreev reflection is observed across the tunnel barrier. From the comparison of Andreev reflection in SrRuO3 and across the CoFe2O4 barrier we infer that the ferrimagnetic barrier has a spin filter efficiency not larger than +13%. The observation of a moderate and positive spin filtering is discussed in the context of the microstructure of the barriers and symmetry-related spin-filtering effects.