Nonmonotonic behavior of the anisotropy coefficient in superconductor-ferromagnet-superconductor trilayer

We have measured critical temperatures and upper critical magnetic fields as a function of the ferromagnetic layer thickness, dF, in two different superconductor(S)/ferromagnet(F)/superconductor(S) triple layers: Nb/Cu0.41Ni0.59 /Nb and Nb/Pd0.81Ni0.19 /Nb. We vary dF from the 0-phase coupling to the pi-phase coupling regime and find strong nonmonotonic behavior of the anisotropy coefficient gammaGL=Hc2par(0)/Hc2perp(0) characterized by an initial increase, a peak, and a subsequent decrease. The peak is a manifestation of the small coupling which exists around the 0-pi transition and it is qualitatively in agreement with recent theoretical predictions [B. Krunavakarn and S. Yoksan, Physica C 440, 25 (2006)] which includes the effect of the different interface transparencies of the two systems. The experimental results demonstrate that the occurrence of the pi phase strongly influences the transport properties of S/F/S systems in external fields.