Transport and critical current measurements in ferromagnetic-superconductor junctions

We carry out transport measurements on Nb/Al/Gd/Al/Nb junctions, Gd being a granular ferromagnet, performed by a superconducting picovoltmeter, Eviden ce of supercurrent through the gadolinium layer is obtained by V-I characte ristic. Well-defined oscillations of critical current with an applied magne tic field confirm the presence of Josephson effect in these junctions. From the critical current measurements, we can deduce a penetration depth of th e Cooper pails in the magnetic layer of 10 Angstrom. (C) 2000 Elsevier Scie nce B.V. All rights reserved.