Phase diagrams of Ba(Fe_1−xM_x)₂As₂ single crystals (M=Rh and Pd)

Single crystalline Ba(Fe_1−xM_x)₂As₂ (M=Rh,Pd) series have been grown and characterized by structural, thermodynamic, and transport measurements. These measurements show that the structural/magnetic phase transitions, found in pure BaFe₂As₂ at 134 K, are suppressed monotonically by the doping and that superconductivity can be stabilized over a domelike region. Temperature-composition (T−x) phase diagrams based on electrical transport and magnetization measurements are constructed and compared to those of the Ba(Fe_1−xM_x)₂As₂ (M=Co,Ni) series. Despite the generic difference between 3d and 4d shells and the specific, conspicuous differences in the changes to the unit cell parameters, the effects of Rh doping are exceptionally similar to the effects of Co doping and the effects of Pd doping are exceptionally similar to the effects of Ni doping. These data show that whereas the structural/antiferromagnetic phase-transition temperatures can be parameterized by x and the superconducting transition temperature can be parameterized by some combination of x and e, the number of extra electrons associated with the M doping, the transition temperatures of 3d- and 4d-doped BaFe₂As₂ cannot be simply parameterized by the changes in the unit-cell dimensions or their ratios.