Suppression of magnetic coupling in superconducting GdN-NbN-GdN trilayers

We report on the effect of superconducting ordering in an NbN spacer layer on the magnetic coupling behavior in GdN-NbN-GdN trilayers. In the normal state of NbN, the weak ferromagnetic semiconductor GdN layers were found to be antiferromagnetically coupled, as inferred from magnetization measurements. A gradual decrease in the coupling strength was observed on cooling through T-c. Although this is to be expected, due to a decrease in the quasiparticle density of states (due to Cooper pairing), there has been no experimental confirmation so far. The gradual decrease in coupling strength above T-c correlates well with the appearance of superconducting fluctuations in the spacer NbN layer. (C) 2013 AIP Publishing LLC.