Magnetic structure and spin-flop transition in the A -site columnar-ordered quadruple perovskite TmMn3O6

We present the magnetic structure of TmMn₃O₆ , solved via neutron powder diffraction. We demonstrate that long-range magnetic order develops below 74 K, and at 28 K a spin-flop transition occurs driven by f -d exchange and rare-earth single-ion anisotropy. In both magnetic phases, the magnetic structure may be described as a collinear ferrimagnet, contrary to conventional theories of magnetic order in the manganite perovskites. Instead, we show that these magnetic structures can be understood to arise due to ferro-orbital order, the A , A^', and A^'' site point symmetry, m m 2 , and the dominance of A -B exchange over both A -A and B -B exchange, which together are unique to the R Mn₃O₆ perovskites.