  The issue of interlayer exchange coupling in magnetic multilayers with
superconducting (SC) spacer is addressed in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$
(LSMO) - YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO) - La$_{0.67}$Sr$_{0.33}$MnO$_{3}$
(LSMO) epitaxial trilayers through resistivity, ac-susceptibility and
magnetization measurements. The ferromagnetic (FM) LSMO layers possessing
in-plane magnetization suppress the critical temperature (T$_{c})$ of the
c-axis oriented YBCO thin film spacer. The superconducting order, however,
survives even in very thin layers (thickness d$_{Y} \sim $ 50 {\AA}, $\sim $ 4
unit cells) at T $<$ 25 K. A predominantly antiferromagnetic (AF) exchange
coupling between the moments of the LSMO layers at fields $<$ 200 Oe is seen in
the normal as well as the superconducting states of the YBCO spacer. The
exchange energy J$_{1}$ ($\sim $ 0.08 erg/cm$^{2}$ at 150 K for d$_{Y}$ = 75
{\AA}) grows on cooling down to T$_{c}$, followed by truncation of this growth
on entering the superconducting state. The coupling energy J$_{1}$ at a fixed
temperature drops exponentially with the thickness of the YBCO layer. The
temperature and d$_{Y}$ dependencies of this primarily non-oscillatory J$_{1}$
are consistent with the coupling theories for systems in which transport is
controlled by tunneling. The truncation of the monotonic T dependence of
J$_{1}$ below T$_{c}$ suggests inhibition of single electron tunneling across
the CuO$_{2}$ planes as the in-plane gap parameter acquires a non-zero value.
