Absence of magnetic proximity effects in magnetoresistive Pt/CoFe2O4 hybrid interfaces

Ultrathin Pt films grown on insulating ferrimagnetic CoFe2O4 (111) epitaxial films display amagnetoresistance upon rotating the magnetization of the magnetic layer. We report here x-ray magnetic circular dichroism (XMCD) recorded at Pt-L-2,L-3 and Pt-M-3 edges. The results indicate that the Pt magnetic moment, if any, is below the detection limit (<0.001 mu B/Pt), thus strongly favoring the view that the presence of CoFe2O4 does not induce the formation of magnetic moments in Pt. Therefore, the observed magnetoresistance cannot be attributed to some sort of proximity-induced magnetic moments at Pt ions and subsequent magnetic-field dependent scattering. It thus follows that either bulk (spin Hall and inverse spin Hall effects) or interface (Rashba) spin-orbit related effects dominate the observed magnetoresistance. Furthermore, comparison of bulk magnetization and XMCD data at (Fe, Co)-L-2,L-3 edges suggests the presence of some spin disorder in the CoFe2O4 layer which may be relevant for the observed anomalous nonsaturating field dependence of spin Hall magnetoresistance.