Microwave-dielectric and magnetic properties of Ta-doped BiFeO_3 nanopowders

摘要

BiFe_(1-x)Ta_xO_3 (x = 0, 0.05, 0.1) nanopowders have been fabricated by a simple sol-gel method. Dielectric measurements at microwave frequencies (2-18 GHz) were made using a vector network analyser. Without tantalum, the BiFeO_3 nanopowder presents a relaxation-like response with a characteristic frequency of 15 GHz, which can be associated with an overdamped process. The Ta-doped nanopowders, however, show resonant behaviour with resonant frequencies of 12.5 and 14.6 GHz. The intensity of the resonant peak near 14.6 GHz decreases with increasing Ta addition. This behaviour is associated with a damped resonance process. Room-temperature magnetic measurements indicate that the addition of Ta influences the magnetic properties of the BiFeO_3 nanopowders, with BiFe_(0.95)Ta_(0.05)O_3 having the strongest ferromagnetism with a saturation magnetisation M_s of about 0.05μ_B/Fe. The origin of the enhanced ferromagnetism is possibly associated with the distortion of the oxygen octahedral by the Ta substitution or/and the statistical distribution of Fe~(3+) and Fe~(2+).