A phenomenological model for magnetoresistance in granular polycrystalline colossal magnetoresistive materials: the role of spin polarised tunnelling at the grain boundaries

TL;DR

This paper introduces a phenomenological model explaining the magnetoresistance behavior in granular CMR materials by considering spin polarized tunnelling at grain boundaries, with applications to specific manganite systems.

Contribution

The paper develops a new phenomenological model that accounts for the magnetic field dependence of resistance in granular CMR materials, emphasizing the role of spin polarized tunnelling at grain boundaries.

Findings

Model fitted to La0.55Ho0.15Sr0.3MnO3 and La1.8Y0.5Ca0.7Mn2O7.

Intrinsic contribution follows double exchange model.

Temperature dependence matches theoretical predictions.

Abstract

It has been observed that in bulk and polycrystalline thin films of collossal magnetoresistive (CMR) materials the magnetoresistance follows a different behaviour compared to single crystals or single crystalline films below the ferromagnetic transition temperature Tc. In this paper we develop a phenomenological model to explain the magnetic field dependence of resistance in granular CMR materials taking into account the spin polarised tunnelling at the grain boundaries. The model has been fitted to two systems, namely, La0.55Ho0.15Sr0.3MnO3 and La1.8Y0.5Ca0.7Mn2O7. From the fitted result we have separated out, in La0.55Ho0.15Sr0.3MnO3, the intrinsic contribution from the intergranular contribution to the magnetoresistance coming from spin polarised tunnelling at the grain boundaries. It is observed that the temperature dependence of the intrinsic contribution to the magnetoresistance in La0.55Ho0.15Sr0.3MnO3 follows the prediction of double exchange model for all values of field.