Synthesis and magnetic properties of quasi-single domain M-type barium hexaferrite powders via sol-gel auto-combustion: Effects of pH and the ratio of citric acid to metal ions (CA/M)

摘要

Quasi-single magnetic domain M-type barium hexaferrite powders have been synthesized via sol-gel auto-combustion route, followed by secondary heating treatment at 800 deg C for 4 h, using barium nitrate, ferrite nitrate, ammonium nitrate, citric acid, and ammonia solution as the starting materials. The auto-combustion producing powders were gamma-Fe_2O_3 and BaCO_3 with aid of additional ammonium nitrate to increase the combustion temperature. The influences of the citric acid to metal ions (CA/M) and pH values on the gel auto-combustion, the phase compositions of the synthesized powders and their magnetic properties have been studied. The results showed that the chelation of barium and ferrite ions were important for the phase formation of barium hexaferrite: the phase compositions of the synthesized powders changed from a multi-phased mixture to a single phase of M-BaFe_(12)O_(19) for the gradually complete com-plexing of barium and iron ions with citrate as the pH values and CA/M increased. The resulting powders demonstrated that various magnetic properties mainly depended on the variation in phase composition, sintering adhesion between grains and grown-up of crystalline sizes. With CA/M = 1.5, pH 7, the synthesized powders had a particle size distribution in the range of 100-200 nm and a saturation magnetization of 58.0 emu/g at l2 kOe.