Transport and Magnetic Properties of Strong Ferromagnetic Pi-Junctions

We have investigated the characteristic voltage dependence with ferromagnetic thickness in Josephson junctions consisting of conventional superconducting Nb electrodes and strongly ferromagnetic barriers: Co, Ni₂₀Fe₈₀(Py) and Ni. Strong oscillations in characteristic voltage suggestive of successive 0-Pi crossovers were observed with the thickness variation of the ferromagnetic layers. Such oscillations show excellent fits to existing theoretical models. The exchange energies of the Co, Py and Ni barriers have been estimated from the periodicity of the oscillations and found to be 309 meV, 201 meV and 80 meV respectively, which is in agreement with previous experimental and theoretical results. We also discuss magnetic behavior of our heterostructures and, in the case of Ni, we have determined its Curie temperature to be sime571 K.