Superlattices of magnetoresistive Ca- and Sr-doped manganese perovskites: Interface effects

Epitaxial superlattices of La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 (LCMO/LSMO)N, grown on SrTiO3, were obtained by the sputtering technique with the same overall thickness (57 nm) but different number of bilayers (N=9,12,17,35). The resulting Tc (around 292 K) is unexpectedly high and close to the LSMO film Tc (305 K). The measured coercive field and saturation magnetization are identical in all of them indicating that interfaces are not playing a direct role in the ferromagnetic interaction, but the volume fraction of paramagnetic Mn increases with the number of interfaces (2N). The MR and residual resistivity behaviors are consistent with the presence of paramagnetic Mn at the interfaces and the narrowing of the magnetic domain walls. At room temperature a high low-field-MR ratio is obtained, about 1% at 500 Oe, but no further increase is detected increasing the number of interfaces.