Resistivity variation in heteroepitaxial La0.7Ca0.3MnO3/Gd0.67Sr0.33MnO3 multilayers with different thicknesses of the La0.7Ca0.3MnO3 layers

Resistivity measurements on La0.7Ca0.3MnO3/Gd0.76Sr0.33MnO3 (LCMO/GSMO) multilayers with different thicknesses of the LCMO layers are reported. The resistivity maximum temperature T-M indicates that the metal-insulator transition decreases with reducing LCMO layer thickness. Data above TM show activated conduction behaviour with rho = CT exp(E-a/k(B) T), the temperature dependence of the conductivity for small-polaron hopping. The activation energy E-a increases with reducing LCMO layer thickness in the multilayers. The explanation of the properties of the LCMO/GSMO multilayers is twofold. For doped manganese oxides, these changes can be understood by (i) considering the effect of strain on the LCMO layers in the LCMO/GSMO multilayers and (ii) assuming that the ferromagnetic transition Curie temperature T-C and E-a depend on the Mn-O-Mn bond angle.