Enhancing low field magnetoresistance in La_0.7Ca_0.25Sr_0.05MnO₃/Mn₃O₄ composite nanoparticles: unveiling its transport mechanism

This work explores the low-field magnetoresistance (LFMR) and transport properties of La_0.7Ca_0.25Sr_0.05MnO₃/Mn₃O₄ composite nanoparticles synthesized via the sol-gel method and sintered at temperatures from 700 °C to 900 °C. We investigate particle size (28–32 nm), Mn₃O₄ fraction, structural phases, and their effects on resistivity and LFMR. Rietveld refinement confirms the coexistence of distorted monoclinic and spinel structures, with an increasing Mn₃O₄ fraction correlating to notable shifts in resistivity and LFMR. Temperature-dependent resistivity measurements reveal a transition from metallic to insulator state, with the 30 nm particle and 19% Mn₃O₄ exhibiting lowest resistivity due to reduce in grain boundary effects and the highest conduction bandwidth. A non-monotonous dependence of resistivity at different particle size and Mn₃O₄ fraction has been observed. It is suggested that resistivity in our composite system is influenced by the interplay of grain boundary contributions, Mn₃O₄ phase distribution, and conduction bandwidth. LFMR reaches up to 30% at 5 K and 5 kOe, exceeding values in similar composite systems. These results emphasize the role of Mn₃O₄ as an insulating phase and highlight the impact of nanoparticle size on the enhancement of LFMR, offering insights into optimizing LFMR in such composites.