Transport mechanism in polycrystallineLa0.825Sr0.175Mn

The transport mechanism of polycrystalline samples ${\mathrm{La}}_{0.825}{\mathrm{Sr}}_{0.175}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Cu}}_{x}{\mathrm{O}}_{3}$ $(0<~x<~0.20)$ and the effects of Cu doping have been investigated. It can be concluded that the existence of Cu induces the superexchange interaction and weakens the long range ferromagnetic order in the samples. The transport mechanism in the metallic regime is attributed to the magnon-carrier scattering and the transport mechanism in the insulating regime transits from polaron transport to variable-range hopping with the adding of Cu. The effect of the surface phase is also observed in the samples.