Persistence of slow fluctuations in the overdoped regime ofBa(Fe1−xRhx)2As2superconductors

We present nuclear magnetic resonance evidence that very slow $(\ensuremath{\le}1$ MHz) spin fluctuations persist into the overdoped regime of $\mathrm{Ba}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Rh}}_{x}){}_{2}{\mathrm{As}}_{2}$ superconductors. Measurements of the $^{75}\mathrm{As}$ spin echo decay rate, obtained both with Hahn Echo and Carr Purcell Meiboom Gill pulse sequences, show that the slowing down of spin fluctuations can be described by short-range diffusive dynamics, likely involving domain walls motions separating $(\ensuremath{\pi}/a,0)$ from $(0,\ensuremath{\pi}/a)$ correlated regions. This slowing down of the fluctuations is weakly sensitive to the external magnetic field and, although fading away with doping, it extends deeply into the overdoped regime.