Emergence of a Magnetostructural Dipolar Glass in the Quadruple Perovskite Dy1−δMn7+δO12

We show that a polar, pseudo-Jahn-Teller instability exists for the underbonded rare-earth $A$-site cations in the quadruple perovskite ${\mathrm{Dy}}_{1\ensuremath{-}\ensuremath{\delta}}{\mathrm{Mn}}_{7+\ensuremath{\delta}}{\mathrm{O}}_{12}$, which leads to the spontaneous formation of a dipolar glass. This observation alone expands the applicability of pseudo-Jahn-Teller physics in perovskite-derived materials, for which it is typically confined to $B$-site cations. We demonstrate that the dipolar glass order parameter is coupled to a ferrimagnetic order parameter via strain, leading to a first order magnetostructural phase transition that can be tuned by magnetic field. This phenomenology may emerge in a broad range of perovskite-derived materials in which $A$-site cation ordering and octahedral tilting are mutually tied to meet the criteria of structural stability.