Superexchange Interaction Energy for Fe3+-O2−-Fe3+ Linkages

Abstract

The superexchange interaction energy for an ${\mathrm{Fe}}^{3+}$-${\mathrm{O}}^{2-}$-${\mathrm{Fe}}^{3+}$ linkage is considered for seven oxides in which ${\mathrm{Fe}}^{3+}$ is the only magnetic ion present, and for magnetite. The superexchange energy may be estimated from the value of $\frac{T_C}{n}$, where $T_C$ is the Curie temperature and $n$ is the number of ${\mathrm{Fe}}^{3+}$-${\mathrm{O}}^{2-}$-${\mathrm{Fe}}^{3+}$ inter-actions per ${\mathrm{Fe}}^{3+}$ ion per formula unit. The average value of $\frac{T_C}{n}$ is 115° (range 106 to 132°). The only compounds considered are antiferromagnetic oxides in which ${\mathrm{Fe}}^{3+}$ ions are present in one set of crystallo-graphically equivalent positions and ferrimagnetic oxides in which ${\mathrm{Fe}}^{3+}$ ions are present in two different sets of crystallographically equivalent positions. No distinct correlation of superexchange energy with ${\mathrm{Fe}}^{3+}$-${\mathrm{O}}^{2-}$ distances or with the included angle in the linkages is evident. Superexchange coupling is considered only for contact distances and for included angles substantially greater than 90°.