Spin Dynamics and Local Inhomogeneity in Doped AFe$_{2}$As$_{2}$ (A = Ca, Ba)

We report $^{75}$As Nuclear Magnetic Resonance (NMR) data in CaFe$_{2}$As$_{2}$, Ba(Fe,Co)$_{2}$As$_{2}$ and Ba(Fe,Ni)$_{2}$As$_{2}$. The static hyperfine field in the antiferromagnetic state is a direct probe of the sublattice magnetization, which decreases with Co or Ni doping. The spectra reveal a broad distribution of local internal fields, consistent with spatial inhomogeneity associated with the dopants. The spin lattice relaxation rate is highly sensitive to the presence of dopants and/or impurities, and reveals the presence of enhanced antiferromagnetic fluctuations with increasing doping. In the antiferromagnetic state, we find that the relaxation is driven by low energy magnon excitations. CaFe$_{2}$As$_{2}$ exhibits an unexpected peak in the spin lattice relaxation rate at 10K that may be driven by glassy dynamics associated with interplanar coupling between different magnetic domains.