  Spin-polarized quasiparticles can be easily created during spin-filtering
through a ferromagnetic insulator (FI) in contact with a superconductor due to
pair breaking effects at the interface. A combination FI-N-FI sandwiched
between two superconductors can be used to create and analyze such
spin-polarized quasiparticles through their nonequilibrium accumulation in the
middle metallic (N) layer. We report spin-polarized quasiparticle regulation in
a double spin-filter tunnel junction in the configuration NbN-GdN1-Ti-GdN2-NbN.
The middle Ti layer provides magnetic decoupling between two ferromagnetic GdN
and a place for nonequilibrium quasiparticle accumulation. The two GdN(1,2)
layers were deposited under different conditions to introduce coercive
contrast. The quasiparticle tunneling spectra has been measured at different
temperatures to understand the tunneling mechanism in these double spin-filter
junctions. The conductance spectra were found to be comparable to an asymmetric
SINI'S-type tunnel junction. A hysteretic R-H loop with higher resistance for
the antiparallel configuration compared to parallel state was observed
asserting the spin-polarized nature of quasiparticles. The hysteresis in the
R-H loop was found to disappear for sub-gap bias current. This difference can
be understood by considering suppression of the interlayer coupling due to
nonequilibrium spin-polarized quasiparticle accumulation in the Ti layer.
