Interplay of magnetism and superconductivity in   EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ single crystals probed by muon spin   rotation and ${}^{57}$Fe M\"ossbauer spectroscopy
  We present our results of a local probe study on EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ single crystals with $x$=0.13, 0.19 and 0.28 by means of muon spin rotation and ${}^{57}$Fe M\"ossbauer spectroscopy. We focus our discussion on the sample with $x$=0.19 viz. at the optimal substitution level, where bulk superconductivity ($T_{\text{SC}}=28$ K) sets in above static europium order ($T^{\text{Eu}}=20$K) but well below the onset of the iron antiferromagnetic (AFM) transition ($\sim$100 K). We find enhanced spin dynamics in the Fe sublattice closely above $T_{\text{SC}}$ and propose that these are related to enhanced Eu fluctuations due to the evident coupling of both sublattices observed in our experiments. 
Til Goltz, Sirko Kamusella, Hirale S. Jeevan, Philipp Gegenwart,   Hubertus Luetkens, Philipp Materne, Johannes Spehling, Ra...
cond-mat.supr-con