Optimally doped mixed valence manganites are considered to be a good source of spin polarized electrons in oxide based magnetic tunneling junctions. However, numerous experiments have shown that magnetic and magnetotransport properties of manganite films deviate strongly from those observed in bulk materials. The presence of ferromagnet/insulator interface seems to influence significantly their half metallic properties. Indeed, ⁵⁵Mn NMR experiments carried out on series of epitaxial La_2/3Ca_1/3MnO₃ (LCMO) films grown on (001) SrTiO₃ (STO) substrates revealed a complex electronic phase separation and an insulating nature of the thinner films. Contributions from manganese atoms in ionic state corresponding to the localized spin states (Mn⁴⁺) as well as Mn^3+/4+ mixed valence state have been identified and attributed to the intrinsic properties of interface, but the driving force behind this phenomenon remained unclear. In this work we present a new approach to this problem: phase separation has been studied as a function of the growth direction of LCMO film. A comparative studies of magnetic properties as well as ⁵⁵Mn NMR study of LCMO films grown on (001) and (110) STO substrates, respectively, have been performed. It has been found that films grown on (110) substrates invariably show improved magnetic properties as compared to their (001) counterparts. In contrast to the results obtained for LCMO(001) films, the ⁵⁵Mn NMR spectra recorded for LCMO(110) films show only a mixed valence Mn^3+/4+ resonance line without any contributions from localized (Mn⁴⁺) charge states. These findings can be interpreted in the context of possible interface reconstruction driven by elastic and electrostatic energies resulting from the lattice mismatch and polarity discontinuity at the LCMO/STO interface.

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1. Magnetic anisotropy and structural properties of ferromagnet/MgO/ferromagnet system