X-ray and Neutron diffraction as well as muon spin relaxation and M\"ossbauer experiments performed on SrFe2As2 polycrystalls confirm a sharp first order transition at T0=205,K corresponding to an orthorhombic phase distortion and to a columnar antiferromagnetic Fe ordering with a propagation vector (1,0,1), and a larger distortion and larger size of the ordered moment than reported for BaFe2As2. The structural and the magnetic order parameters present an remarkable similarity in their temperature dependence from T0 down to low temperatures, showing that both phenomena are intimately connected. Accordingly, the size of the ordered Fe moments scale with the lattice distortion when going from SrFe2As2 to BaFe2As2. Full-potential band structure calculations confirm that the columnar magnetic order and the orthorhombic lattice distortion are intrinsically tied to each other.
@article{arxiv.0807.0632,
title = {Strong coupling between magnetic and structural order parameters in SrFe2As2},
author = {A. Jesche and N. Caroca-Canales and H. Rosner and H. Borrmann and A. Ormeci and D. Kasinathan and K. Kaneko and H. H. Klauss and H. Luetkens and R. Khasanov and A. Amato and A. Hoser and C. Krellner and C. Geibel},
journal= {arXiv preprint arXiv:0807.0632},
year = {2008}
}