Specific heat, resistivity, magnetic susceptibility, linear thermal expansion (LTE), and high-resolution synchrotron X-ray powder diffraction investigations of single crystals Fe1+yTe (0.06 < y < 0.15) reveal a splitting of a single, first-order transition for y < 0.11 into two transitions for y > 0.12. Most strikingly, all measurements on identical samples Fe1.13Te consistently indicate that, upon cooling, the magnetic transition at T_N precedes the first-order structural transition at a lower temperature T_s. The structural transition in turn coincides with a change in the character of the magnetic structure. The LTE measurements along the crystallographic c-axis displays a small distortion close to T_N due to a lattice striction as a consequence of magnetic ordering, and a much larger change at T_s. The lattice symmetry changes, however, only below T_s as indicated by powder X-ray diffraction. This behavior is in stark contrast to the sequence in which the phase transitions occur in Fe pnictides.
@article{arxiv.1209.1209,
title = {First-order structural transition in the magnetically ordered phase of Fe1.13Te},
author = {S. Rößler and Dona Cherian and W. Lorenz and M. Doerr and C. Koz and C. Curfs and Yu. Prots and U. K. Rößler and U. Schwarz and Suja Elizabeth and S. Wirth},
journal= {arXiv preprint arXiv:1209.1209},
year = {2012}
}