The Bean critical state model in a superconductor with a magnetically-ordered sublattice: the case of RbEuFe₄As₄

The magnetically ordered, relatively low-anisotropy superconductor RbEuFe₄As₄, displaying a remarkably high superconducting transition temperature of T_c ~37 K and magnetic transition temperature T_m ~15 K, may host topological states and is an excellent platform for investigating interactions between magnetism and superconductivity. In high-quality single crystals, an anomalous suppression of the superconducting magnetization hysteresis occurs below the magnetic ordering temperature at the saturation field of the helical Eu-spin lattice when the magnetic field is applied in-plane. This suggests, via the Bean critical state model, that novel pinning effects are active in the state of the non-collinear magnetic structure which disappear at the saturation field. However, we argue that a modification to the Bean model incorporating the presence of large magnetic moments implies that the superconducting critical current is actually weakly impacted by the magnetic order.