Temperature evolution of the magnetic structure of TbMn2O5

We have investigated the ordered magnetic structures of TbMn2O5 and their temperature evolution using single-crystal neutron Laue diffraction. From a least-squares fit to diffraction intensities extracted from the Laue patterns recorded at varying angles at T = 2 K, we were able to refine a magnetic structure model to obtain the magnetic-twin populations, three components of moment for each of the four independent Mn and two independent Tb sublattices, together with phase factors for all of these sublattices. The temperature evolution of the magnetic structures was followed from fixed crystal-orientation Laue patterns collected at close temperature intervals between 2 and 38 K. Least-squares refinement of data extracted from these patterns showed that although the magnetic propagation vector tau changes abruptly in the temperature ranges 20-22 and 35-37 K, the magnetic structural motif remains essentially the same in all of the ordered phases, although some of the parameters, in particular the orientation angles, change significantly at the lower temperature transition. The observation of significant 3 tau reflections in the Laue diagrams between 2 and 20 K shows that the magnetic modulation is nonsinusoidal in this temperature range.