We investigate the thermodynamic and transport properties of molybdenum-doped BaFe${}_2$As${}_2$ (122) crystals, the first report of hole doping using a 4$d$ element. The chemical substitution of Mo in place of Fe is possible up to ∼ 7$\%$. For Ba(Fe${}_{1-x}$Mo${}_x$)${}_2$As${}_2$, the suppression rate of the magnetic transition temperature with $x$ is the same as in 3$d$ Cr-doped 122 and is independent of the unit cell changes. This illustrates that the temperature-composition phase diagram for hole-doped 122 can be simply parameterized by $x$, similar to the electron-doped 122 systems found in the literature. Compared to 122 with a coupled antiferromagnetic order ($T_N$) and orthorhombic structural transition ($T_0$) at ≈132 K, 1.3$\%$ Mo-doped 122 ($x=0.013$) gives $T_N=T_0=125\left(1\right)$ K according to neutron diffraction results and features in specific heat, magnetic susceptibility, and electrical resistivity. The cell volume expands by ∼1$\%$ with maximum Mo doping and $T_N$ is reduced to ≈90 K. There is a $T^{*}$ feature that is identified for lightly Cr- or Mo-doped 122 crystals, which is $x$ dependent. This low-temperature transition may be a trace of superconductivity.

• Received 19 October 2011

DOI:https://doi.org/10.1103/PhysRevB.85.024503