Spin Frustration Drives Exchange Bias Sign Crossover in CoFe₂O₄–Cr₂O₃ Nanocomposites

Abstract A combined Raman spectroscopy and magnetometry study of CoFe 2 O 4 –Cr 2 O 3 nanocomposites demonstrates the presence of spin–phonon interactions and exchange bias at the interface between the ferrimagnetic CoFe 2 O 4 and the antiferromagnetic and magnetoelectric Cr 2 O 3 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 CoFe 2 O 4 or decreasing the percentage of Cr 2 O 3 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.