Magnetic transitions in exotic perovskites stabilized by chemical and physical pressure

Exotic perovskites significantly enrich materials for multiferroic and magnetoelectric applications. However, their design and synthesis is a challenge due to the mostly required recipe conditions at extremely high pressure. Herein, we presented the Ca2-xMnxMnTaO6 (0 <= x <= 1.0) solid solutions stabilized by chemical pressure assisted with intermediate physical pressure up to 7 GPa. The incorporation of Mn2+ into the A-site neither drives any cationic ordering nor modifies the orthorhombic Pbnm structure, namely written as (Ca1-x/2Mnx/2)(Mn1/2Ta1/2)O-3 with disordered A and B site cationic arrangements. The increment of x is accompanied by a ferromagnetic to antiferromagnetic transition around x = 0.2, which is attributed to the double-exchange interactions between A-site Mn2+ and B-site Mn3+. Partial charge disproportionation of the B-site Mn3+ into Mn2+ and Mn4+ occurs for x above 0.8 samples as manifested by X-ray spectrum and magnetic behaviors. The coexistence of B-site Mn3+ (Jahn-Teller distortion ion) and B '-site Ta5+ (second-order Jahn-Teller distortion ion) could be energetically responsible for the absence of A-site columnar ordering as observed in other quadruple perovskites with half of the A-sites occupied by small transition-metal cations. These exceptional findings indicate that exotic perovskites can be successfully stabilized at chemical and intermediate physical pressure, and the presence of Jahn-Teller distortion cations at the same lattice should be avoided to enable cationic ordering.