Emergence of a Magnetostructural Dipolar Glass in the Quadruple Perovskite Dy_{1-δ}Mn_{7+δ}O_{12}

Robust Crystal Phase Separation with Distinct Charge, Orbital, and Spin Orders in AgMn7O12

An AA'3B4O12-type A-site-ordered quadruple perovskite oxide AgMn7O12 was prepared by high-pressure and high-temperature methods. At room temperature, the compound crystallizes into a cubic Im3̅ symmetry with a charge distribution of AgMn33+Mn43.5+O12. With the temperature decreasing to TCO,OO ≈ 180 K, the compound undergoes a structural phase transition toward a monoclinic C2/m symmetry, giving rise to a B-site charge- and orbital-ordered AgMn33+Mn23+Mn24+O12 phase. Moreover, this charge-/orbital-ordered main phase coexists with the initial cubic AgMn33+Mn43.5+O12 phase in the wide temperature range we measured. The charge-/orbital-ordered phase shows two antiferromagnetic phase transitions near 125 and 90 K, respectively. Short-range ferromagnetic correlations are found to occur for the initial B-site mixed cubic phase around 35 K. Because of the robust phase separation, considerable magnetoresistance effects are observed below TCO,OO in AgMn7O12.

The rich physics of A-site-ordered quadruple perovskite manganites AMn7O12

Perovskite-structure AMnO₃ manganites played an important role in the development of numerous physical concepts such as double exchange, small polarons, electron-phonon coupling, and Jahn-Teller effects, and they host a variety of important properties such as colossal magnetoresistance and spin-induced ferroelectric polarization (multiferroicity). A-site-ordered quadruple perovskite manganites AMn₇O₁₂ were discovered shortly after, but at that time their exploration was quite limited. Significant progress in their understanding has been reached in recent years after the wider use of high-pressure synthesis techniques needed to prepare such materials. Here we review this progress, and show that the AMn₇O₁₂ compounds host rich physics beyond the canonical AMnO₃ materials.