Robust Crystal Phase Separation with Distinct Charge, Orbital, and Spin Orders in AgMn 7 O 12 .

An AA' 3 B 4 O 12 -type A-site-ordered quadruple perovskite oxide AgMn 7 O 12 was prepared by high-pressure and high-temperature methods. At room temperature, the compound crystallizes into a cubic Im 3̅ symmetry with a charge distribution of AgMn 3 3+ Mn 4 3.5+ O 12 . With the temperature decreasing to T CO,OO ≈ 180 K, the compound undergoes a structural phase transition toward a monoclinic C 2/ m symmetry, giving rise to a B-site charge- and orbital-ordered AgMn 3 3+ Mn 2 3+ Mn 2 4+ O 12 phase. Moreover, this charge-/orbital-ordered main phase coexists with the initial cubic AgMn 3 3+ Mn 4 3.5+ O 12 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 T CO,OO in AgMn 7 O 12 .