  We present a muon spin rotation (\muSR) study of the magnetic and
superconducting properties of single crystals of electron-doped BaFe2-xCoxAs2
with x=0.08, 0.20, and 0.25 (Tc=9, 25 and 20K) and of polycrystalline
hole-doped Pr1-xSrxFeAsO with x=0 and 0.2 (Tc=15 K). In the former series we
observe some interesting parallels with the electron doped SmFeAsO1-xFx
1111-type system [A.J. Drew et al., to appear in Nature Materials 2009 and
arXiv:0807.4876]. In particular, we obtain evidence that strongly disordered
static magnetism coexists with superconductivity on a microscopic scale in
underdoped samples and even at optimum doping there is a slowing down (or
enhancement) of dynamic magnetic correlations below Tc\approx25K. To the
contrary, for the hole-doped Pr1-xSrxFeAsO samples we obtain evidence for a
mesoscopic phase segregation into regions with nearly unperturbed AF order and
others that are non magnetic and most likely superconducting. The observed
trend resembles the one that was previously reported for hole-doped
Ba1-xKxFe2As2 [A.A. Aczel et al., Phys. Rev. B 78, 214503 (2008); J.T. Park et
al., arXiv:0811.2224] and thus seems to be fairly common in these hole doped
systems.
