Peculiar magnetism of BiFeO(3) nanoparticles with size approaching the period of the spiral spin structure

Size effect of multiferroics is important for its potential applications in new type miniaturized multifunctional devices and thus has been widely studied. However, is there special size effect in the materials with spiral modulated spin structure (such as BiFeO(3))? It is still an issue to be investigated. In this report, structural, magnetic and magnetoelectric coupling properties are investigated for sol-gel prepared BiFeO(3) nanoparticles with various sizes. It is found that a structural anomaly arises for the particles with size close to the 62 nm period of the spiral modulated spin structure, which induces an obviously increased ferromagnetism. In addition, large magnetoelectric coupling effect is observed in 62 nm BiFeO(3) nanoparticles. Our result provides another insight into the size effect of BiFeO(3), and also a clue to the magnetic structure at nanoscale.