Triple A-Site Cation Ordering in the Ferrimagnetic YCuGaMnO Perovskite.

A new member of A-site columnar-ordered AA'A″BO quadruple perovskites with the composition of YCuGaMnO 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: [Y][CuMn][GaMn][MnCuGa]O. It has the space group 4/ (no. 137) between 1.5 and 873 K with = 7.33884 Å and = 7.66251 Å at 297 K. Despite anti-site disorder, it exhibits a long-range ferrimagnetic order at = 115 K with the ordered moment of 2.19 μ at each B site and 0.89 μ at the A' or A″ site. Magnetic moments are aligned along the 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. Cu doping drastically changes magnetic properties as "parent" YMnGaMnO just shows spin-glass magnetic properties without long-range ordering. Anisotropic thermal expansion was observed in YCuGaMnO: the lattice parameter almost linearly decreases from 1.5 K to and then monotonically increases up to 873 K (almost linearly from 300 K); the parameter monotonically increases from 1.5 to 300 K and then decreases up to 600 K.