Relationship Between Crystal Symmetry and Magnetic Properties of Ionic Compounds ContainingMn3+

An investigation has been made of the relationship between crystallographic symmetry and ${\mathrm{Mn}}^{3+}$ - ${\mathrm{O}}^{2-}$ - ${\mathrm{Mn}}^{3+}$ 180° superexchange interactions in several perovskite systems. In particular, crystallographic and magnetic measurements have been made on a number of samples in the systems $\mathrm{La}\left({\mathrm{Mn}}_{1-x}{M}_x\right){\mathrm{O}}_{3+\delta }$, where $M=\mathrm{G}\mathrm{a},\mathrm{C}\mathrm{o},\mathrm{N}\mathrm{i}$. In all three systems, the ${\mathrm{Mn}}^{3+}$ - ${\mathrm{O}}^{2-}$ - ${\mathrm{Mn}}^{3+}$ interactions are found to be ferromagnetic for $O$-orthorhombic samples having $a<\mathrm{}\frac{c}{\sqrt{2}}<b$. For $x<\mathrm{}0.5\mathrm{}$ in the system $M=\mathrm{Ga}$, there is $O^{\prime }$-orthorhombic symmetry ($\frac{c}{\sqrt{2}}<a<b$) and ferrimagnetism that is suggestive of anisotropic ${\mathrm{Mn}}^{3+}$ - ${\mathrm{O}}^{2-}$ - ${\mathrm{Mn}}^{3+}$ interactions, similar to those found in LaMn${\mathrm{O}}_3$, and preferential ordering of the ${\mathrm{Ga}}^{3+}$ into one magnetic sublattice. Measurements of Curie temperature vs composition in this system support ordering of the gallium in the compositional range $x\le 0.4$, partial ordering in the range $0.4<x\le 0.6$. These observations are consistent with the magnetic measurements of various other workers on the systems $(\mathrm{La}, M^{\prime 2+})\mathrm{Mn}{\mathrm{O}}_{3+\delta }$, La(Mn,Cr)${\mathrm{O}}_3$ (La,Ba) (Mn,Ti)${\mathrm{O}}_3$.