Proximity effects in superconductor-ferromagnet junctions

We have studied electron transport in Sn-Ni-Sn structures, in which the Ni had the form of a narrow (similar to 400 Angstrom wide) wire. The behaviour is very sensitive to the quality of the Ni-Sn interface. With a clean inte rface, there appears to be a significant proximity effect in the Ni, and th e results imply an unexpectedly long proximity length. However, when an oxi de layer is present at the Sn-Ni interface, the effective resistance of the Ni increases as the temperature is reduced below the critical temperature, T-c, of the Sn. It does not appear that these observations can be explaine d by current theories.