Effects of post-growth heat treatment on electronic phase diagrams and critical current densities of Ba(Fe1−xCox)2As2 and BaFe2(As1−xPx)2 single crystals

In this paper, we investigated the effects of annealing on the physical properties of $\mathrm{Ba}{(\mathrm{F}{\mathrm{e}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{o}}_{x})}_{2}\mathrm{A}{\mathrm{s}}_{2}$ and $\mathrm{BaF}{\mathrm{e}}_{2}{(\mathrm{A}{\mathrm{s}}_{1\ensuremath{-}x}{\mathrm{P}}_{x})}_{2}$ single crystals systematically. In both systems, the effects of annealing on the phase transition temperatures and the critical current density ${J}_{\mathrm{c}}$ are contrasting; the superconducting and magnetostructural transition temperatures ${T}_{\mathrm{c}}$ and ${T}_{\mathrm{sN}}$, respectively, increased for all doping levels after annealing, whereas the critical current density ${J}_{\mathrm{c}}$ only increased around the optimally doped region while it decreased in the other regions. These facts indicate that the changes in ${T}_{\mathrm{c}}$ and ${J}_{\mathrm{c}}$ caused by annealing are governed by different mechanisms and that the mechanism for ${J}_{\mathrm{c}}$ varies depending on the doping level. The results demonstrate that the enhancement of ${T}_{\mathrm{c}}$ and ${T}_{\mathrm{sN}}$ as well as the decrease of ${J}_{\mathrm{c}}$ can be attributed to the reduction of disorder, while the enhancement of ${J}_{\mathrm{c}}$ is associated with the enhanced pinning arising from the antiferromagnetic-orthorhombic phase mixed into the superconducting phase.