  Artificially engineered superlattices were designed and fabricated to induce
different growth mechanisms and structural characteristics. DC sputtering was
used to grow ferromagnetic (La$_{0.8}$Ba$_{0.2}$MnO$_3$) / ferroelectric
(Ba$_{0.25}$Sr$_{0.75}$TiO$_3$ or BaTiO$_3$) superlattices. We systematically
modified the thickness of the ferromagnetic layer to analyze dimensional and
structural effects on the superlattices with different structural
characteristics. The crystalline structure was characterized by X-Ray
diffraction and transmission electron microscopy. The magnetic and electronic
properties were investigated by SQUID magnetometry and resistance measurements.
The results show that both strain and structural disorder can significantly
affect the physical properties of the systems. Compressive strain tends to
increase the competition between the magnetic interactions decreasing the
ferromagnetism of the samples and the localization of the charge carrier
through the electron-phonon interaction. Tensile strain reduces the charge
carrier localization, increasing the ferromagnetic transition temperature.
Structural defects have a stronger influence on the magnetic properties than on
the transport properties, reducing the ferromagnetic transition temperature
while increasing the magnetic hardness of the superlattices. These results help
to further understand the role of strain and interface effects in the magnetic
and transport properties of manganite based multiferroic systems.
