Unusual Evolution of the Magnetic Interactions versus Structural Distortions inRMnO3Perovskites

We report the refinement of x-ray powder diffraction together with magnetic and thermal conductivity measurements made on the entire family of $R{\mathrm{MnO}}_3$ perovskites prepared by melt growth or under high pressure. Analysis of the data has identified the origin of the transition from type-$A$ to type-$E$ magnetic order as a competition between $t$-orbital and $e$-orbital spin-spin interactions within each Mn-O-Mn bond in the (001) planes, the $e$-orbital interactions decreasing with decreasing $R^{3+}$-ion size.