  This paper reports the observation of hysteresis in the vortex pinning in a
superconductor / ferromagnetic epitaxial nanocomposite consisting of fcc Gd
particles incorporated in a Nb matrix. We show that this hysteretic pinning is
associated with magnetic reversal losses in the Gd particles and is
fundamentally different in origin to pinning interactions previously observed
for ferromagnetic particles or other microstructural features.
