Phase diagram of a superconductor/ferromagnet bilayer

The magnetic-field--temperature (H-T) phase diagram of a superconductor is significantly altered when domains are present in an underlying ferromagnet with perpendicular magnetic anisotropy. When the domains have a bandlike shape, the critical temperature Tc of the superconductor in zero field is strongly reduced and the slope of the upper critical field as a function of T is increased by a factor of 2.4 due to the inhomogeneous stray fields of the domains. Field compensation effects can cause an asymmetric phase boundary with respect to H when the ferromagnet contains bubble domains. For a very inhomogeneous domain structure, Tc∝H² for low H and Tc∝H for higher fields, indicating a dimensional crossover from a one-dimensional networklike to a two-dimensional behavior in the nucleation of superconductivity.