  Ferromagnetic/metallic manganese perovskites, such as La2/3Sr1/3MnO3
(LSMO)are promising materials for the design and implementation of novel
spintronic devices working at room temperature. However, their implementation
in practical applications has been severely hampered due to the breakdown of
their magnetotransport properties at temperatures well below their magnetic
transition temperature. This breakdown has been usually associated to surface
and interface related problems but its physical origin has not been clearly
established yet. In this work we investigate the interface between
La2/3Sr1/3MnO3 (LSMO) thin films and different capping layers by means of x-ray
linear dichroism and transport measurements. Our data reveal that, irrespective
to the capping material, LSMO/capping layer bilayers exhibit an
antiferromegnetic/insulating phase at the interface, likely to originate from a
preferential occupancy of Mn 3d 3z2-r2 eg orbitals. This phase, which extends
ca. 2 unit cells, is also observed in an uncapped LSMO reference sample thus,
pointing to an intrinsic interfacial phase separation phenomenon, likely to be
promoted by the structural disruption and symmetry breaking at the LSMO free
surface/interface. These experimental observations strongly suggest that the
structural disruption at the LSMO interfaces play a major role on the observed
depressed magnetotransport properties in manganite-based magnetic tunneling
junctions and it is at the origin of the so-called dead layer.
