Influence of isovalent and heterovalent substitution for Bi3+ and Fe3+ on the properties of Bi2Fe4O9-based solid solutions

Bi 2– х La х Fe 4 O 9 and Bi 2 Fe 4–2 x Ti x Co x O 9 ferrites have been prepared by solid-state reactions at a temperature of 1073 K. X-ray diffraction data indicate that, in the Bi 2– х La х Fe 4 O 9 system, the limiting degree of La 3+ substitution for Bi 3+ ions in Bi 2 Fe 4 O 9 does not exceed 0.05 and that the limiting degree of substitution in the Bi 2 Fe 4–2 x Ti x Co x O 9 system lies in the range 0.05 < x < 0.1. The specific magnetization and specific magnetic susceptibility of the samples have been measured at temperatures from 5 to 300 K in a magnetic field of 0.86 T. The field dependences of magnetization obtained for the Bi 2– х La х Fe 4 O 9 and Bi 2 Fe 4–2 x Ti x Co x O 9 ferrites at temperatures of 300 and 5 K demonstrate that partial isovalent substitution of La 3+ for Bi 3+ ions in Bi 2 Fe 4 O 9 and heterovalent substitution of Ti 4+ and Co 2+ ions for two Fe 3+ ions leads to partial breakdown of the antiferromagnetic state and nucleation of a ferromagnetic state.