Microstructures, Magnetic Properties and Specific Absorption Rate of Polymer-Modified Bismuth Ferrite Nanoparticles

Bismuth ferrite nanoparticles were successfully synthesized by the co-precipitation method and modified by polyethylene glycol (PEG) 4000. X-ray diffraction patterns showed a sillenite structure of bismuth ferrite (Bi25FeO40) with a crystallite size of 35.0 nm, and the new phase appeared after surface modification. The new phase was Bi2Fe4O9. Crystallite size increased after surface modification of nanoparticles with PEG. The highest increase of crystallite size after surface modification with PEG was 40.1 nm. Transmission electron microscopy images showed that samples before and after surface modification were polycrystalline and still agglomerated. Spectra of Fourier transform infrared showed the presence of C-O stretching at 1080 cm-1 and C-H bending vibration at 1342 cm-1 in the bismuth ferrite/PEG sample, which did not appear in the bismuth ferrite sample. The magnetic measurement indicated the weak ferromagnetic properties of the samples. Saturation magnetization did not appear after applying a maximum external magnetic field (15 kOe). The maximum magnetization of nanoparticles was 0.5 emu/g and tended to decrease to 0.2 emu/g after surface modification with PEG. Optical properties analysis showed a shift in the maximum absorption peak of bismuth ferrite nanoparticles towards a lower wavelength (blue shift) after surface modification of the nanoparticles. The specific absorption rate (SAR) value of nanoparticles increased by increasing an alternating magnetic field (AMF) strength. The SAR values of bismuth ferrite nanoparticles were 48.8, 61.4, and 84.4 mW/g and decreased to 32.0, 45.2, and 83.3 mW/g after surface modification at the AMF strength of 150, 200, and 250 Oe, respectively.