Magnetic Proximity Effect in Pt/CoFe₂O₄ Bilayers

We observe the magnetic proximity effect (MPE) in Pt/CoFe₂O₄ bilayers grown by molecular beam epitaxy (MBE). This is revealed through angle-dependent magnetoresistance measurements at 5 K, which isolate the contributions of induced ferromagnetism (i.e. anisotropic magnetoresistance) and spin Hall effect (i.e. spin Hall magnetoresistance) in the Pt layer. The observation of induced ferromagnetism in Pt via AMR is further supported by density functional theory calculations and various control measurements including 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 MPE in Pt/CoFe₂O₄, these results establish the spinel ferrite family as a promising material for MPE and spin manipulation via proximity exchange fields.