The magnetic structures of the rare-earth manganates ErMn2O5and TbMn2O5

The magnetic structures of the orthorhombic rear-earth manganates ErMn 2 O 5 and TbMn 2 O 5 have been studied by single-crystal neutron diffraction at temperatures between 1.5 and 25 K. Both materials exhibit amplitude-modulated magnetic structures with propagation vector (0.5, 0, 0.247) (Er) or (0.5, 0, 0.308) (Tb) and moment directions in the ac plane (Er) or the ab plane (Tb). The measurements indicate that the Mn 4+ and Mn 3+ ionic moments are almost fully magnetically ordered at all the observed temperatures but that the rare-earth ions show an increasing degree of magnetic order at the lower temperatures. The detailed magnetic structures are significantly different from those already in the literature, which are based on powder neutron diffraction data.