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⁺Mn₄^3.5+O₁₂. With the temperature decreasing to T_CO,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⁺Mn₄^3.5+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.