The structure and magnetic properties of pure single phase BiFeO3 nanoparticles by microwave-assisted sol-gel method

The pure single phase BiFeO3 nanoparticles have been prepared by microwave-assisted sol-gel process and its structure and magnetic properties have been studied. X-ray diffractometer, infrared and transmission electron microscope results show that the synthesized BiFeO3 nanoparticles at the calcining temperature of 450 °C exhibits a rhombohedrally distorted perovskite structure without secondary phase and the size is about 40 nm. Meanwhile, the pure single phase BiFeO3 particles exhibit typical ferromagnetic properties at room temperature and the obvious large exchange bias phenomenon at 60 K. A exchange bias field (HE) of 302 Oe at 60 K for pure single phase BiFeO3 nanoparticles at calcining temperature 450 °C after field cooling at 20 KOe has been observed. The MT curve at H = 100 Oe shows that the FC and ZFC magnetization curves start to differ in the temperature range from 60 K to 300 K revealing spin glass behavior of BiFeO3 nanoparticles at calcining temperature 450 °C, 500 °C and 550 °C. The ferromagnetic behavior is attributed to size of effects, which partially destroy the long-wavelength cycloid spin structure expected in bulk BiFeO3. The exchange bias effect in single crystalline BiFeO3 nanoparticles arises from co-existence of different magnetic phases of an antiferromagnetic core and a ferromagnetic surface. The ferromagnetic, exchange bias effect and spin glass behavior of BiFeO3 nanoparticles are assigned to the uncompensated or canted spins at the ferromagnetic surface and an antiferromagnetic core of BiFeO3 nanoparticles.