Bernhard, Christian Wang, Chen Nan Nuccio, Laura Schulz, Leander Zaharko, O. Larsen, J. Aristizabal, C. Willis, M. Drew, Alan J. Varma, G. D. Wolf, T. Niedermayer, Ch. 2012-10-19 Using muon spin rotation (μSR) we investigated the magnetic and superconducting properties of a series of Ba(Fe_1−xCo_x)₂As₂ single crystals with 0≤x≤0.15. Our study details how the antiferromagnetic order is suppressed upon Co substitution and how it coexists with superconductivity. In the nonsuperconducting samples at 0<x<0.04 the antiferromagnetic order parameter is only moderately suppressed. With the onset of superconductivity this suppression becomes faster and it is most rapid between x=0.045 and 0.05. As was previously demonstrated by μSR at x=0.055 [ P. Marsik et al. Phys. Rev. Lett. 105 57001 (2010)], the strongly weakened antiferromagnetic order is still a bulk phenomenon that competes with superconductivity. The comparison with neutron diffraction data suggests that the antiferromagnetic order remains commensurate whereas the amplitude exhibits a spatial variation that is likely caused by the randomly distributed Co atoms. A different kind of magnetic order that was also previously identified [ C. Bernhard et al. New J. Phys. 11 055050 (2009)] occurs at 0.055<x<0.075 where T_c approaches the maximum value. The magnetic order develops here only in parts of the sample volume and it seems to cooperate with superconductivity since its onset temperature coincides with T_c. Even in the strongly overdoped regime at x = 0.11, where the static magnetic order has disappeared, we find that the low-energy spin fluctuations are anomalously enhanced below T_c. These findings point toward a drastic change in the relationship between the magnetic and superconducting orders from a competitive one in the strongly underdoped regime to a constructive one in near-optimally and overdoped samples. application/pdf https://folia.unifr.ch/global/documents/302716 https://folia.unifr.ch/documents/302716/files/ber_msr.pdf eng info:eu-repo/semantics/altIdentifier/doi/10.1103/PhysRevB.86.184509 info:eu-repo/semantics/openAccess License undefined Physical Review B - Condensed Matter and Materials Physics. - 2012, vol. 86, no. 14, p. 144112 info:eu-repo/classification/udc/53 Muon spin rotation study of magnetism and superconductivity in Ba(Fe_1−xCo_x)₂As₂ single crystals http://purl.org/coar/resource_type/c_6501