Charge Transport and Magnetoresistive Mechanisms in Samarium-Doped Manganite Nanoparticles and Their Polypyrrole Nanocomposite

Le résumé fourni par la source

A detailed investigation of charge transport, encompassing direct-current (DC) and alternating-current (AC) conduction, was performed for samarium-doped manganite nanoparticles and their polypyrrole (PPy)-based nanocomposites. The electrical transport characteristics of the pristine manganite and nanocomposite systems were examined as a function of temperature, magnetic field and samarium concentration. The pristine manganite exhibits characteristic polycrystalline magnetoresistance (MR), with MR increasing from ~55% for the lowest samarium concentration (M1) to ~75% for the highest concentration (M5) at 50 K. Spin-polarized tunneling across grain boundaries constitutes the dominant MR mechanism, with the temperature dependence supporting the role of suppressed spin fluctuations. The nanocomposites exhibit anomalous, fluctuation-like field-dependent MR behaviour that varies with temperature and samarium concentration, with the effect being most pronounced at lower samarium concentrations over the 50-250 K temperature range. This behaviour is attributed to the competition between weak localization and charge-carrier delocalization within a core-shell architecture, mediated by intermediate exchange coupling and the incorporation of polypyrrole. The distinct transport and magnetoresistance responses of the manganite nanoparticles and PPy-based nanocomposites provide insight into the interplay between grain-boundary effects, magnetic exchange interactions and polymer-mediated charge transport.

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