Magnetic Structures of High Temperature Phases of TbBaCo₂O_5.5

Abstract

Neutron diffraction studies have been carried out on a single crystal of\noxygen-deficient perovskite TbBaCo2O5.5 in the temperature range of 7-370 K.\nThere have been observed several magnetic or structural transitions. Among\nthese, the existence of the transitions to the insulating phase from the\nmetallic one at ~340 K, to the one with the ferromagnetic moment at ~280 K and\npossibly to the antiferromagnetic one at ~260 K, with decreasing temperature T\ncorrespond to those reported in former works. We have studied the magnetic\nstructures at 270 K and 250 K and found that all Co3+ ions of the CoO6\noctahedra are in the low spin state and those of the CoO5 pyramids carry spins\nwhich are possibly in the intermediate spin state. Non-collinear magnetic\nstructures are proposed at these temperatures. Two other transitions have also\nbeen observed at the temperatures, ~100 K and ~250 K.\n