Magnetic field dependence of parallel spin stripe order in La1.6−xNd0.4SrxCuO4 at optimal doping

Elastic neutron scattering measurements have been carried out on a single crystal of La1.6−xNd0.4SrxCuO4 at optimal doping for superconductivity, x = 0.19, in magnetic fields up to 8 T, applied ∥c. At zero magnetic field, these measurements of the intensity of parallel spin stripe quasi-Bragg peaks show a departure from a weak sloping background below TN = 40 K, with a ∼ linear growth in intensity that is bounded between superconducting Tc(onset) = 26 K and Tc(mid) = 13 K. Below Tc(mid), the order parameter plateaus and subsequently displays a strong increase below TNd∼ 8 K. This strong, low-temperature increase is due to weak coupling between the magnetism in the CuO2 planes and that of Nd3+ moments between the planes. A magnetic field ∥c> 1.5 T suppresses this low-temperature rise of the order parameter, as the Nd3+ moments polarize in the field, and the coupled Nd3+-CuO2 magnetism can no longer participate in the incommensurate, parallel spin stripe structure. At T=10K, above TNd but below Tc(mid), the stripe intensity weakly decreases with field, consistent with vortex-induced disorder of short-range stripes in d-wave superconducting regions. For T≥17K, no measurable field dependence is observed, showing that a uniform H∥c<8 T does not perturb CuO2 stripe magnetism. A plateau at Tc(mid) persists across all fields. These results are discussed in the context of earlier studies of the magnetic field dependence on parallel spin stripes in La1.6−xNd0.4SrxCuO4, La2−xSrxCuO4, and La2−xBaxCuO4.