Muon spin rotation study of magnetism and superconductivity in BaFe2-xCoxAs2 and Pr1-xSrxFeAsO

TL;DR

This study uses muon spin rotation to investigate the coexistence and phase separation of magnetism and superconductivity in electron- and hole-doped iron-based superconductors, revealing microscopic coexistence in electron-doped and mesoscopic segregation in hole-doped samples.

Contribution

It provides new insights into the magnetic and superconducting phase coexistence and segregation in doped BaFe2-xCoxAs2 and Pr1-xSrxFeAsO compounds using bmuSR techniques.

Findings

Disordered static magnetism coexists with superconductivity in underdoped electron-doped samples.

Dynamic magnetic correlations slow down below Tc in optimally doped electron-doped samples.

Hole-doped Pr1-xSrxFeAsO exhibits mesoscopic phase segregation into magnetic and non-magnetic regions.

Abstract

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.