Size-dependent electronic-transport mechanism and sign reversal of magnetoresistance in Nd0.5Sr0.5CoO3

TL;DR

This study explores how grain size reduction in Nd0.5Sr0.5CoO3 induces a metal-insulator transition, alters electron interactions, and reverses magnetoresistance sign due to increased disorder and phase separation.

Contribution

It provides new insights into size-dependent electronic transport mechanisms and magnetoresistance behavior in Nd0.5Sr0.5CoO3, highlighting the role of disorder and phase separation.

Findings

Size-induced metal-insulator transition at nanoscale

Electron-electron interaction dominates resistivity behavior

Magnetoresistance sign reversal with decreasing grain size

Abstract

A detailed investigation of electronic-transport properties of Nd0.5Sr0.5CoO3 has been carried out as a function of grain size ranging from micrometer order down to an average size of 28 nm. Interestingly, we observe a size induced metal-insulator transition in the lowest grain size sample while the bulk-like sample is metallic in the whole measured temperature regime. An analysis of the temperature dependent resistivity in the metallic regime reveals that the electron-electron interaction is the dominating mechanism while other processes like electron-magnon and electron-phonon scatterings are also likely to be present. The fascinating observation of enhanced low temperature upturn and minimum in resistivity on reduction of grain size is found due to electron-electron interaction (quantum interference effect). This effect is attributed to enhanced disorder on reduction of grain size. Interestingly, we observed a cross over from positive to negative magnetoresistance in the low temperature regime as the grain size is reduced. This observed sign reversal is attributed to enhanced phase separation on decreasing the grain size of the cobaltite.