Abstract
The compounds ATiTO 5 are isomorphous with HoMn 2O 5 when the rare earth ionic radius is intermediate between that of Gd and Pr. Pyrochlore (T 2Ti 2O 7) and perowskite (ATO 3) structures are found simultaneously. A purpose of this study was to investigate the distribution of A 3+ and Ti 4+ in ATiTO 5 over the two different available sites having an octahedral and square pyramid oxygen environment. A neutron diffraction study of Nd compounds has shown that A 3+ occupation of the octahedral site was 95% and 57% when A 3+ is Cr 3+ and Fe 3+ respectively. This is easily interpreted using crystal field theory. In CrTiNdO 5 both Cr and Nd spins become ordered below 13°K Nd 3+ spins lie in the XY plane (+GxAy). Cr 3+ ions in octahedral sites (95%) have spins along the z axis (+Az) while the remaining Cr 3+ ions square pyramid sites (5%) have spins in the XY plane (+Ay). Shubnikov group is Pbam'. In FeTiNdO 5, Nd 3+ spins are not ordered at 1·5°K Fe 3+ spins lie in XY plane with a CxFy configuration for both sites. Shubnikov group is P 2 cb ' am'. For these two compounds the spin direction in the XY plane makes an angle of approximately 12° with the Y axis. In CrTiNdO 5 the spin direction can be explained only by assuming anisotropic exchange. No magnetic ordering was observed for MnTiNdO 5.
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