Effect of single Hf~(4+) ion substitution on microstructure and magnetic properties of hexagonal M-type Ba(Hf)_xFe_(12-x)O_(19) ferrites

摘要

Hf~(4+) substituted M-type hexaferrites with composition of BaHf)_xFe_(12-x)O_(19)(x = 0-0.08 in step of 0.02 ) were synthesized via a solid reaction method. Pure M phase was observed by XRD analysis excepted when x = 0.08, the second phase (HfO_2) appeared when x = 0.08. With increase of the Hf~(4+) substitution contents, the average grain size decreased, the shape of grains became irregular gradually and some small particles appeared and spacing between grains increased. It could be explained by lattice distortion and the agglomeration of grains. In terms of magnetic properties, the saturation magnetization (M_s) decreased from 81.16 emu/g to 38.36 emu/g and the coercivity (H_c) increased from 666 Oe to 1220 Oe as x increased from 0.00 to 0.08, which might be attributed to occupancies of Hf~(4+) ions on 2b sublattice. This would result in a valence change of Fe~(3+) to Fe~(2+) at the 2a site. Moreover, the magnetocrystalline anisotropy of the samples maintained a high level and changed slightly, while the saturation magnetization of the samples decreased to a low level, which provided a choice for magnetic materials to meet higher frequency applications.