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