Fluctuations in the local fields due to Al³⁺ ions substitution in the M-type barium hexaferrites, BaFe_12-xAl_xO₁₂

The effects of aluminum substitution into the M-type Ba-hexaferrites on the saturation magnetization and Mossbauer spectrum of these ferrites are studied. The saturation magnetization M_s of the BaFe_12-xAl_xO₁₂ is seen to decrease linearly with increasing Al substitution. The Mossbauer spectrums for the x = 0.1, 0.2 and 0.6 specimens were all resolved as superpositions of four sub-spectrums (12k, 4f_iv + 2a, 4f_vi and 4e). The half width of the Mossbauer lines of the 4f_iv + 2a sextets is seen to broadening as Al ions are substituted into the ferrite. No broadening is seen in the lines of the other sextets. These behaviors (the line broadening and the linear decrease in M_s) are consistent with the Al³⁺ ions substituting preferentially into the 2a sites.