  This thesis presents a systematic study of magnetotransport and magnetic
ordering in manganite-high T$_c$ cuprate spin valve structures.
YBa$_{2}$Cu$_{3}$O$_{7}$ - La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ heterostructures
of (110) orientation are grown to allow direct injection of spin polarized
holes from the La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ (LSMO) into the CuO$_2$
superconducting planes of the YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO). Galvanomagnetic
studies on the LSMO-YBCO-LSMO trilayers reveal unusually high AMR
($\sim$72000%) on rotating the field in the plane of the heterostructure whose
magnetic ground state is antiferromagnetic (AF). The coupling energy J$_1$ of
the AF state in these trilayers is much higher as compared to energy of (001)
oriented hybrids. First the preparation and measurement of magnetic and
galvanomagnetic properties of (110) and (001) oriented La$_{2 / 3}$Sr$_{1 /
3}$MnO$_{3}$ films are described. The magnetization vector ($\vec{M}$) of the
(001) and (110) type films is pinned along the (110) and (001) directions
respectively at low fields. A magnetization orientation phase transition (MRPT)
which manifests itself as a discontinuity and hysteresis in $R(\psi)$ where
$\psi$ is the angle between $\vec{H}$ and the easy axis for the $\vec{H}$ below
a critical value $\vec{H}^*$ has been established. Further, the relevance of
pair-breaking by exchange and dipolar fields, and by injected spins in a low
carrier density cuprate Y$_{1-x}$Pr$_x$Ba$_2$Cu$_3$O$_7$ sandwiched between two
ferromagnetic LSMO layers is examined. At low external field ($H_{ext}$), the
system shows a giant magnetoresistance(MR), which diverges deep in the
superconducting state.
