Flux expulsion and reversible magnetization in the stripe phase superconductor La1.45Nd0.40Sr0.15CuO4

Magnetization and free energy surfaces have been studied for superconducting La1.45Nd0.40Sr0.15CuO4 in order to determine whether this stripe-phase material has a thermodynamic critical field curve, Hc, similar to the classical superconductors. A large region of thermodynamic reversibility is found so that magnetization and free energy surfaces can be determined reliably over much of the H-T plane. In these stripe-phase materials there is evidence from neutron scattering that the holes collect in the domain walls of the antiphase domain structure, so the superconducting order parameter might be space dependent and the vortex lattice might be different from ordinary type-II superconductors. Although some uncertainty is introduced because a substantial background magnetization from the magnetic Nd ions must be subtracted, it can be stated that the Hc vs T curve is found to be comparable to Nb. The material is a good bulk superconductor, but the shape of the magnetization curves (Ms vs H) is quite different from the predictions of conventional type-II superconductor theories. copyright 1997 The American Physical Society