Effects of magnetic order on the superconducting length scales and critical fields in single crystal ErNi2B2C

The flux line form factor in small angle neutron scattering and transport d ata determines the superconducting length scares and critical fields in sin gle crystal ErNi2B2C. For H parallel to c, the coherence length xi increase s and the penetration depth lambda decreases when crossing T-N = 6.0 K, the Neel transition. The critical fields show corresponding anomalies near T-N . For H perpendicular to c, the fourfold modulation of the upper critical f ield H-c2 is strongly temperature dependent, changing sign near T-N, and ca n be modeled using the anisotropy of the sublattice magnetization.