  We present a new study of magnetic structures with controllable effective
exchange energy for Josephson switches and memory. As a basis for a weak link
we propose to use a periodic structure comprised of ferromagnetic (F) layers
spaced by thin superconductors (s). Our calculations based on Usadel equations
show that switching from parallel (P) to antiparallel (AP) alignment of
neighboring F layers can lead to a significant enhancement of the critical
current through the junction. To control magnetic alignment we propose to use
periodic system where unit cell is a pseudo spin-valve $F_1$/s/$F_2$/s with
$F_1$ and $F_2$ two magnetic layers having different coercive fields. In order
to check feasibility of controllable switching between AP and P states through
the \emph{whole} periodic structure we prepared a superlattice
[Co(1.5nm)/Nb(8nm)/Co(2.5nm)/Nb(8nm)]$_6$ between two superconducting layers of
Nb(25nm). Neutron scattering showed that parallel and antiparallel alignment
can be organized by using of magnetic fields of only several tens of Oersted.
