Local measurement of the penetration depth in the pnictide superconductor Ba(Fe_0.95Co_0.05)₂As₂

We use magnetic force microscopy (MFM) to measure the local penetration depth λ in Ba(Fe_0.95Co_0.05)₂As₂ single crystals and use scanning superconducting quantum interference device susceptometry to measure its temperature variation down to 0.4 K. We observe that superfluid density ρ_s over the full temperature range is well described by a clean two-band fully gapped model. We demonstrate that MFM can measure the important and hard-to-determine absolute value of λ, as well as obtain its temperature dependence and spatial homogeneity. We find ρ_s to be uniform on the submicron scale despite the highly disordered vortex pinning.