Saturation magnetization of some ferrimagnetic oxides with hexagonal crystal structures

Anderson´s treatment of super-exchange yields a qualitative rule for the dependence of interaction on angle Me¿O¿Me. Using this rule, and assuming a longer distance to lead to a weaker interaction, low-temperature saturation magnetizations for ferrimagnetic oxides with known crystal structures can often be predicted. The results obtained for some of the materials described in Ref. 1, i.e. Ba2MeII2Fe12O22 (Y), Ba3MeII2Fe24O41 (Z),and BaMeII2Fe16O27 (W) (in which Me may be MeII may be Mn, Fe, Co, Ni, Mg, or Zn), together with those for BaFe12O19 (M) and KFe11O17 with related crystal structures, are compared with the results of saturation-magnetization measurements down to 20°¿K. It is shown that very small differences in crystal structure, such as exist between KFeO17 and M, and between M and Y, can result in drastic differences in spin orientations of neighbouring ions. In particular for Y, the experimental data yield some insight into the distribution of the divalent Me ions among the various lattice sites. The crystal structure of Z is composed of alternating blocks of M and Y, that of W is composed of alternating blocks of M and S (spinel). The saturation magnetizations are obtained by adding those of the composing blocks.