Coexistence of ferromagnetic and superconducting domains in Co-doped BaFe2 As2 superconductors probed using infrared Faraday measurements

We explore the electronic and magnetic properties of superconducting iron pnictide films by probing their infrared Hall conductivity as a function of probe energy (0.1-1.3 eV), temperature (10-300 K) and magnetic field (B = 0-7 T). We find hysteretic behavior in the complex infrared Faraday angle, $\theta_{F}$, at lowB over the entire temperature range. At higher $B, \theta_{\mathrm{F}}$ is linear in B and we observe a peak in the high B -field slope near 50 K, which may be related to the superconducting phase of the films.