Impact of silver substitution on the magnetotransport and thermal behavior of polycrystalline Sm0.55Sr0.45−xAgxMnO3 (x = 0 & 0.15) manganites

We have synthesized a series of Sm0.55Sr0.45−xAgxMnO3 (x = 0 & 0.15) by conventional solid state reaction method to scrutinize the effect of monovalent Ag+ as a replacement of Sr2+ ion on structural, electrical, magnetotransport and thermoelectric properties. The structural parameters obtained using Rietveld refinement of X-ray diffraction data which showed perovskite structure having orthorhombic (Pnma) symmetry without any detectable impurity phase. It is observed that MZFC and MFC curves become more manifested as Ag+ content is increased which indicates an increase in magnetic frustration arising due to bending of Mn-O-Mn bond. The M-H plots show the narrow hysteresis loops which indicate the soft ferromagnetic nature. Magnetic studies also show that the Curie temperature TC is found to decrease with Ag+ content. The metal-insulator transition temperature (TMI) is observed which decreases with the increase of Ag+ content when magnetic field is applied. The resistivity data in high temperature region are explained within the framework of variable range hopping (VRH) and small polaron hopping (SPH) models. The thermoelectric power (S) of the reported samples exhibits a crossover from positive to negative value and value of S increases in doped samples. The analysis of thermoelectric power data confirms that the small polaron hopping model in high temperature region and at low temperature electron-magnon scattering is the dominating in the FM region. With increasing the Ag+ content the samples showed very high magneto-resistance (MR%) and temperature coefficient of resistance (TCR%) which make the compound more promising for scientific and technological applications.