Magneto-optical imaging of iron-oxypnictide SmFeAsO1−xFx and SmFeAsO1−y

We have prepared iron-oxypnictide SmFeAsO1−xFx by ambient-pressure technique and SmFeAsO1−y by high-pressure technique, and characterized their bulk and local magnetic properties by using SQUID magnetometer and magneto-optical imaging. While the high-pressure samples have densities close to the theoretical value, the ambient-pressure samples have several small voids. Despite these structural differences between the two kinds of samples, they both have superconducting transition temperature above 50 K. In addition, magneto-optical images for both samples show similar kinds of inhomogeneities with large current concentrated in several grains and with small intergranular current. The estimated intragranular currents for both samples are over 105 A/cm2 at low temperatures and low fields.