Substitutional effects on structural and magnetotransport properties of La0.85−xSmxK0.15MnO3 (x = 0.05, 0.1 and 0.15)

A series of polycrystalline La0.85−xSmxK0.15MnO3 (x = 0.05, 0.1 and 0.15) have been synthesized by standard solid state reaction method to study effects of substituting La3+ by Sm3+ ion on the structural, electrical and magnetic properties. The Rietveld refinement of X-ray diffraction data revealed that mixed valence manganites crystallize in rhombohedral structure (space group R3¯C, no. 167). Raman spectra at room temperature reveal gradual change in phonon modes on increased doping. The temperature dependent electrical resistivity is measured by a standard four-probe method between 5 and 300 K. The temperature dependent electrical resistivity exhibits metal-insulator transition at temperature TMI and metallic state (T < TMI) signifies importance of electron-electron, electron-phonon and electron-spin fluctuation scattering process. The peak resistivity ρm increases rapidly with Sm and TMI shifts to a lower temperature. The high temperature (T > TMI) conductivity data signifies polaronic nature. Application of magnetic field suppresses resistivity in entire temperature range. Low temperatures resistivity infers a field-dependent minimum and is due to electron-electron interaction and Kondo effects of mixed valence manganites. The ferro to paramagnetic transition temperature (TC) decreases with decreasing ionic radius as well as one-electron bandwidth of the A-site cation.