  The crystalline structure, anisotropic magnetoresistance (AMR), and
magnetization of La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) superlattices grown by an rf
sputtering system are systematically analyzed to study the spin polarization of
manganite at interfaces. A perfectly epitaxial growth with sharp interfaces
between LSMO and STO layers is confirmed by the transmission electron
microscopy (TEM) image and the x-ray diffraction. The presence of positive
low-temperature AMR in LSMO/STO superlattices with thinner LSMO layers or
thicker STO layers implies that two bands of majority and minority character
contribute to the transport properties, leading to a reduced spin polarization.
Furthermore, the magnetization of superlattices follows the T3/2 law at low
temperatures and decays more quickly as the thickness ratio dSTO/dLSMO
increases, corresponding to a reduced exchange coupling. The results clearly
show that the spin polarization is strongly correlated with the influence of
interface-induced strain on the structure.
