Magneto-optical imaging of polycrystalline LaFePO1−xFx

Abstract

The remanent state field profile has been observed in polycrystalline LaFePO0.94F0.06 by magneto-optical (MO) imaging method. MO images show the absence of magnetic field modulation associated with weak-link nature of grain boundaries, indicating that the inter-grain critical current density Jcinter is comparable to intra-grain critical current density Jcintra in contrast to iron-arsenide superconductors. Jcinter is estimated as 1.9×104A/cm2 at T=0K from magnetization measurement, which is similar to the values in iron-arsenide superconductors. Implication of these Jc behavior is discussed in relation to the possible pairing symmetry.