Triple A-Site Cation Ordering in the Ferrimagnetic Y2CuGaMn4O12 Perovskite

A new member of A-site columnar-ordered A₂A'A″B₄O₁₂ quadruple perovskites with the composition of Y₂CuGaMn₄O₁₂ was prepared by a high-pressure, high-temperature method at 6 GPa and about 1500 K. Its crystal structure and cation distributions were studied by powder synchrotron X-ray and neutron diffraction. There is a triple A-site cation ordering with some degrees of anti-site disorder among sites occupied by 3d transition metals: [Y₂]_A[Cu_0.8Mn_0.2]_A'[Ga_0.8Mn_0.2]_A″[Mn_3.6Cu_0.2Ga_0.2]_BO₁₂. It has the space group P4₂/nmc (no. 137) between 1.5 and 873 K with a = 7.33884 Å and c = 7.66251 Å at 297 K. Despite anti-site disorder, it exhibits a long-range ferrimagnetic order at T_C = 115 K with the ordered moment of 2.19 μ_B at each B site and 0.89 μ_B at the A' or A″ site. Magnetic moments are aligned along the c axis; all moments are ordered ferromagnetically at the B sites, and the moments at the A' or A″ site are ordered in the opposite direction. Cu²⁺ doping drastically changes magnetic properties as "parent" Y₂MnGaMn₄O₁₂ just shows spin-glass magnetic properties without long-range ordering. Anisotropic thermal expansion was observed in Y₂CuGaMn₄O₁₂: the lattice parameter a almost linearly decreases from 1.5 K to T_C and then monotonically increases up to 873 K (almost linearly from 300 K); the parameter c monotonically increases from 1.5 to 300 K and then decreases up to 600 K.