Abstract
We use bulk magnetic susceptibility, electronic specific heat, and neutron scattering to study structural and magnetic phase transitions in . 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 the 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 and FeAs-based pnictides are expected to have similar Fermi surfaces and therefore the same spin-density wave AF order.
- Received 2 November 2008
DOI:https://doi.org/10.1103/PhysRevB.79.054503
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