  Magnetization measurements in superconductor/ferromagnet Nb/Co superlattices
show a complex behavior as a function of temperature, applied field and sample
history. In base to a simple model it is shown that this behavior is due to an
interplay between the superconductor magnetization temperature dependence, the
ferromagnet magnetization time dependence, and the stray fields of both
materials. It is also shown that the magnetic state of the Co layers is
modified by the Nb superconducting response, implying that the problem of a
superconductor/ferromagnetic heterogeneous sample has to be solved in a
self-consistent manner.
