Competing superconducting and magnetic order parameters and field-induced magnetism in electron-dopedBa(Fe1−xCox)2As2

Abstract

This paper presents a systematic study of 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. Calculations based on the five-band Hubbard Hamiltonian reproduce the physical properties of the coexistence region of Ba(Fe${}_{1-x}$Co${}_{x}$)${}_{2}$As${}_{2}$. Below the superconducting transition temperature the magnetic and superconducting order parameters coexist and compete. An external magnetic field significantly enhances the magnetic order parameter within the superconducting state. This behavior can be caused by the vortices, which in the superconducting state can slow down and locally freeze spin fluctuations.