Antiferromagnetic ordering in the absence of structural distortion inBa(Fe1−xMnx)2As2

Abstract

Neutron and x-ray diffraction studies of $\text{Ba}{({\text{Fe}}_{1\ensuremath{-}x}{\text{Mn}}_{x})}_{2}{\text{As}}_{2}$ for low doping concentrations $(x\ensuremath{\le}0.176)$ reveal that at a critical concentration, $0.102<x<0.118$, the tetragonal-to-orthorhombic transition abruptly disappears whereas magnetic ordering with a propagation vector of $(\frac{1}{2}\text{ }\frac{1}{2}\text{ }1)$ persists. Among all of the iron arsenides this observation is unique to Mn doping, and unexpected because all models for ``stripelike'' antiferromagnetic order anticipate an attendant orthorhombic distortion due to magnetoelastic effects. We discuss these observations and their consequences in terms of previous studies of $\text{Ba}{({\text{Fe}}_{1\ensuremath{-}x}T{M}_{x})}_{2}{\text{As}}_{2}$ compounds $(TM=\text{transition}\text{ }\text{metal})$, and models for magnetic ordering in the iron arsenide compounds.