The exchange bias behavior of BiFeO 3 nanoparticles with natural core-shell structure.

The surface and interface effects of small antiferromagnetic nanostructures are important on the modulation of their magnetic properties. In this report, temperature and particle size dependent magnetic exchange bias effect was investigated in BiFeO ₃ (BFO) nanoparticles that possess natural core-shell structure. Nonmonotonic variation of exchange bias field, interesting surface spin-glass state and improved exchange bias training effect are only obtained in 18 nm BFO particles. Based on comparative experiments on particles with different sizes, we found that the surface spins and the interaction among them show great effect on the interfacial exchange coupling of the core-shell structure, and thus are responsible for the peculiar exchange bias behavior in small BFO nanoparticles. Our work provides the effect of surface spin state on the magnetic characteristics of nanomaterials and will favor their applications on spintronic devices.