Competing superconducting and magnetic order parameters and field-induced magnetism in electron doped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}

• Main Authors: Larsen, J, Uranga, B. Mencia, Stieber, G, Holm, S. L, Bernhard, C, Wolf, T, Lefmann, K, Andersen, B. M, Niedermayer, C
• Format: Journal Article
• Language: English
• Published: 27.11.2014
• Subjects: Physics - Superconductivity
• DOI: 10.48550/arxiv.1411.7506

Phys. Rev. B 91, 024504 (2015) We have studied the magnetic and superconducting properties of Ba(Fe$_{0.95}$Co$_{0.05}$)$_{2}$As$_{2}$ as a function of temperature and external magnetic field using neutron scattering and muon spin rotation. Below the superconducting transition temperature the magnetic and superconducting order parameters coexist and compete. A magnetic field can significantly enhance the magnetic scattering in the superconducting state, roughly doubling the Bragg intensity at 13.5 T. We perform a microscopic modelling of the data by use of a five-band Hamiltonian relevant to iron pnictides. In the superconducting state, vortices can slow down and freeze spin fluctuations locally. When such regions couple they result in a long-range ordered antiferromagnetic phase producing the enhanced magnetic elastic scattering in agreement with experiments.