Magnetic proximity effect in Pt/CoFe2O4 bilayers

We observe the magnetic proximity effect (MPE) in Pt/CoFe2O4 bilayers grown by molecular beam epitaxy. This is revealed through angle-dependent magnetoresistance measurements at 5K, which isolate the contributions of induced ferromagnetism (i.e., anisotropic magnetoresistance) and the spin Hall effect (i.e., the spin Hall magnetoresistance) in the Pt layer. The strong evidence for induced ferromagnetism in Pt via the anisotropic magnetoresistance is supported further by density functional theory calculations and various control measurements including the insertion of a Cu spacer layer to suppress the induced ferromagnetism. In addition, anomalous Hall effect measurements show an out-of-plane magnetic hysteresis loop of the induced ferromagnetic phase with larger coercivity and larger remanence than the bulk CoFe2O4. By demonstrating the MPE in Pt/CoFe2O4, these results establish the spinel ferrite family as a promising material for the MPE and spin manipulation via proximity exchange fields.