Spin Frustration Drives Exchange Bias Sign Crossover In Cofe2o4-Cr2o3 Nanocomposites

A combined Raman spectroscopy and magnetometry study of CoFe2O4-Cr2O3 nanocomposites demonstrates the presence of spin-phonon interactions and exchange bias at the interface between the ferrimagnetic CoFe2O4 and the antiferromagnetic and magnetoelectric Cr2O3 phases. The pinned layer of uncompensated spins at the surface of the chromium oxide nanocrystals provides a source of unidirectional anisotropy and changes the sign of the exchange bias when transitioning from a canted to a frustrated situation, that is, as increasing the percentage of CoFe2O4 or decreasing the percentage of Cr2O3 in the composites. This assessment of the distinctive interfaces attained in the final oxide heterostructures offers a prospective route for hybrid materials which uphold a magnetoelectric effect.