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

An AA'BO-type A-site-ordered quadruple perovskite oxide AgMnO was prepared by high-pressure and high-temperature methods. At room temperature, the compound crystallizes into a cubic 3̅ symmetry with a charge distribution of AgMnMnO. With the temperature decreasing to ≈ 180 K, the compound undergoes a structural phase transition toward a monoclinic 2/ symmetry, giving rise to a B-site charge- and orbital-ordered AgMnMnMnO phase. Moreover, this charge-/orbital-ordered main phase coexists with the initial cubic AgMnMnO 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 in AgMnO.