We use bulk magnetic susceptibility, electronic specific heat, and neutron scattering to study structural and magnetic phase transitions in Fe1+ySe% xTe1−x. Fe1.068Te exhibits a first order phase transition near 67 K with a tetragonal to monoclinic structural transition and simultaneously develops a collinear antiferromagnetic (AF) order responsible for the entropy change across the transition. Systematic studies of FeSeTex system reveal that the AF structure and lattice distortion in these materials are different from those of FeAs-based pnictides. These results call into question the conclusions of present density functional calculations, where FeSe1−xTex and FeAs-based pnictides are expected to have similar Fermi surfaces and therefore the same spin-density-wave AF order.
@article{arxiv.0811.0195,
title = {First-order magnetic and structural phase transitions in Fe$_{1+y}$Se$_x$Te$_{1-x}$},
author = {Shiliang Li and Clarina de la Cruz and Q. Huang and Y. Chen and J. W. Lynn and Jiangping Hu and Yi-Lin Huang and Fong-chi Hsu and Kuo-Wei Yeh and Maw-Kuen Wu and Pengcheng Dai},
journal= {arXiv preprint arXiv:0811.0195},
year = {2009}
}