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, mm2, and the dominance of A-B exchange over both A-A and B-B exchange, which together are unique to the RMn3O6 perovskites.