Suppression of antiferromagnetic order and orthorhombic distortion in superconducting Ba(Fe0.961Rh0.039)2As2

Neutron-diffraction and high-resolution x-ray diffraction studies find that, similar to the closely related underdoped Ba(Fe1-xCox)(2)As-2 superconducting compounds, Ba(Fe0.961Rh0.039)(2)As-2 shows strong evidence of competition and coexistence between superconductivity and antiferromagnetic order below the superconducting transition, T-c=14 K. The transition temperatures for both the magnetic order and orthorhombic distortion are in excellent agreement with those inferred from resistivity measurements, and both order parameters manifest a distinct decrease in magnitude below T-c. These data suggest that the strong interaction between magnetism and superconductivity is a general feature of electron-doped Ba(Fe1-xTMx)(2)As-2 superconductors (TM=transition metal).