We present a detailed investigation of the magnetic and superconducting properties of Ca1-xNaxFe2As2 single crystals with x = 0.00, 0.35, 0.50, and 0.67 by means of the local probe techniques Moessbauer spectroscopy and muon spin relaxation experiments. With increasing Na substitution level, the magnetic order parameter as well as the magneto-structural phase transition are suppressed. For x = 0.50 we find a microscopic coexistence of magnetic and superconducting phases accompanied by a reduction of the magnetic order parameter below the superconducting transition temperature Tc. A systematic comparison with other 122 pnictides reveals a square-root correlation between the reduction of the magnetic order parameter and the ratio of the transition temperatures, Tc/TN, which can be understood in the framework of a Landau theory. In the optimally doped sample with Tc = 34 K, diluted magnetism is found and the temperature dependence of the penetration depth and superfluid density are obtained, proving the presence of two superconducting s-wave gaps
@article{arxiv.1505.00962,
title = {Microscopic coexistence of superconductivity and magnetism in Ca1-xNaxFe2As2},
author = {Philipp Materne and Sirko Kamusella and Rajib Sarkar and Til Goltz and Johannes Spehling and Hemke Maeter and Luminita Harnagea and Sabine Wurmehl and Bernd Buechner and Hubertus Luetkens and Carsten Timm and Hans-Henning Klauss},
journal= {arXiv preprint arXiv:1505.00962},
year = {2015}
}