Transport–magnetism correlations in (1 −  <i>x</i> ) La0.67Ca0.33MnO3:( <i>x</i> ) Ag2O perovskite manganite-composites

Abstract

In this paper, we report a comprehensive study on the correlation between electrical resistivity (ρ) and magnetization (M) in La0.67Ca0.33MnO3 (LCMO) polycrystalline-composite with Ag2O, synthesized by a conventional solid-state reaction method. The introduction of Ag2O modifies the intergranular regions without altering the intrinsic perovskite lattice and leads to distinct effects in different temperature regimes. At low temperatures, grain-boundary contributions dominate the total magnetoresistance through spin-polarized tunneling, which is significantly suppressed in the Ag2O composites due to the formation of additional conductive pathways between grains. At higher temperatures, improved intergranular connectivity shifts the metal–insulator transition temperature (TM-I) closer to the Curie temperature (TC), resulting in a clear correlation between transport and magnetism, with charge transport below TC governed by a polaron hopping mechanism. The sharpening of TM-I in the Ag2O composites leads to a substantial enhancement in magnetoresistance, reaching ∼68.6% at 270 K (x=0.15) under a magnetic field of 20 kOe, which is about 60% higher than pristine LCMO, along with a temperature coefficient of resistance of ∼21%, corresponding to a threefold improvement. Importantly, the strong ρ–M correlation enables a transport-based estimation of the isothermal magnetic entropy change (−ΔSM) from resistivity measurements performed across TM-I/TC, showing good agreement with values obtained using Maxwell relations. A maximum −ΔSM of 5.15 J kg−1 K−1 is obtained near 271 K, while the temperature-averaged entropy change (TEC) over a broad temperature span is estimated to be 5 J kg−1 K−1 [TEC(3)] and 4.6 J kg−1 K−1 [TEC(10)] for a field change of 20 kOe. These results highlight the correlation between transport, magnetism, and magnetocaloric response in manganite perovskites when grain-boundary effects are effectively controlled.