Ferromagnetic ordering and electromagnons in microwave synthesized BiFeO3 thin films

Bismuth iron oxide sols are synthesized using microwave radiations with variation in microwave power in the range of 180 W-1000 W. Magnetic analysis of bismuth iron oxide sols indicate ferromagnetic behavior at microwave powers of 540-720 W. Paramagnetic behavior is observed at microwave powers of 180 W and 270 W. Mixed ferromagnetic and antiferromagnetic behavior of sols is obtained at microwave power of 360 W, 450 W and 810 W-1000 W. Sols synthesized using microwaves are spin coated onto copper substrates and annealed at 300 degrees C, in the presence of magnetic field, to obtain bismuth iron oxide thin films. X-ray diffraction patterns of thin films indicate amorphous behavior at low microwave power of 180 W and 270 W. Mixed BiFeO3 and Bi25FeO40 phases are obtained at microwave powers of 360 W and 450 W. Transition to phase pure BiFeO3 takes place at microwave power of 540-720 W. Mixed BiFeO3 and Bi2Fe4O9 phases are obtained at high microwave powers of 810 W-1000 W. Energy dispersive X-ray spectrum also confirms formation of BiFeO3 phase with 66.21%, 17.63% and 15.20% for Bi, Fe and O, respectively. Strong ferromagnetic behavior with low magnetocrystalline anisotropy is observed for films prepared using microwave power of 540-720 W. High saturation magnetization of 26.38 emu/cm(3) is obtained at microwave power of 720 W. Field cooled and zero-field cooled magnetization curves show spin orientation transition at similar to 80 K. Low temperature Raman analysis indicates presence of electromagnons with anomaly observed at 80 K.