Magnetic properties of Ni-substituted BiFeO3

BiFe1−xNixO3 ceramic powders with x up to 0.10 have been prepared by the sol–gel technique. The band gap of BiFeO3 is 2.23 eV, and decreases to 2.09 eV for BiFe0.95Ni0.05O3 and BiFe0.90Ni0.10O3. The Mössbauer spectra show sextet at room temperature, indicating the magnetic ordering and the presence of only Fe3+ ions. Superparamagnetism with blocking temperature of 31 K for BiFe0.95Ni0.05O3 and 100 K for BiFe0.90Ni0.10O3 was observed. Enhanced magnetization at room temperature have been observed (1.0 emu/g for BiFe0.95Ni0.05O3 and 2.9 emu/g for BiFe0.90Ni0.10O3 under magnetic field of 10,000 Oe), which is one order larger than that of BiFeO3 (0.1 emu/g under magnetic field of 10,000 Oe). The enhanced magnetization was attributed to the suppression of the cycloidal spin structure by Ni3+ substitution and the ferrimagnetic interaction between Fe3+ and Ni3+ ions.