Electrical Transport Study of Patterned Lateral Niobium-Permalloy Junctions

In order to investigate the interplay between magnetic domain walls and superconductivity we study the electrical transport property of lateral Nb-permalloy-Nb junctions where the permalloy thickness is varied from 50 to 90 nm. Magnetic force microscopy images confirm the presence of domain walls in the ferromagnetic portion between the two superconducting electrodes for samples with permalloy thickness of 60, 70 and 90 nm. Below superconducting transition temperature, the zero bias conductance (ZBC) for these samples shows a sharp reduction in the magnetic field range of 0 to 0.15 T and after that it stays almost at a constant level until a high field is applied. The phenomenon is attributed to domain wall assisted crossed Andreev reflection (CAR) and/or long range triplet component (LRTC) of superconductivity. On the contrary, the decreasing trend of ZBC at low field is absent for the sample with 50 nm thick NiFe which indicates that the conductance contribution from CAR and/or LRTC is absent in this sample. This is presumably due the fact that the permalloy in the gap region for this sample is in a single domain state. A quantitative analysis for conductance contribution from domain wall assisted CAR is provided.