We report a combined experimental and theoretical investigation of the layered antimonide PrMnSbO which is isostructural to the parent phase of the iron pnictide superconductors. We find linear resistivity near room temperature and Fermi liquidlike $T^2$ behavior below 150 K. Neutron powder diffraction shows that unfrustrated C-type Mn magnetic order develops below $\sim 230\text{K}$, followed by a spin flop coupled to induced Pr order. At $T\sim 35\text{K}$, we find a tetragonal to orthorhombic (T-O) transition. First-principles calculations show that the large magnetic moments observed in this metallic compound are of local origin. Our results are thus inconsistent with either the itinerant or frustrated models proposed for symmetry breaking in the iron pnictides. We show that PrMnSbO is instead a rare example of a metal where structural distortions are driven by $f$-electron degrees of freedom.

• Received 22 July 2010

DOI:https://doi.org/10.1103/PhysRevB.82.100412