Transition from a ferromagnetic insulating to a ferromagnetic metallic state in nanoparticles of Nd0.8Sr0.2MnO3 : Study of the electronic - and magneto - transport properties

TL;DR

This study reveals that reducing grain size in Nd0.8Sr0.2MnO3 nanoparticles suppresses the ferromagnetic insulating state and induces a metallic state, highlighting the role of surface disorder and polaron destabilization in electronic and magnetic phase transitions.

Contribution

It demonstrates the transition from insulating to metallic behavior in low-doped manganite nanoparticles due to grain size reduction and surface effects, supported by a phenomenological model.

Findings

Ferromagnetic insulating state is suppressed in nanoparticles.

Metal-insulator transition occurs with decreasing grain size.

Surface disorder destabilizes polaronic order in nano grains.

Abstract

A detailed investigation of the electronic - and magneto - transport properties of Nd0.8Sr0.2MnO3 with the variation of grain size (down to 42 nm) is presented here. Interestingly, we observe that the ferromagnetic insulating state is suppressed and a metallic state is stabilized as the grain size of the sample is reduced. As a result, metal insulator transition is observed in this low doped manganite which is insulating in nature in its bulk form. Destabilization of polaronic order in the ferromagnetic insulating state due to enhanced surface disorder on grain size reduction has been attributed to this effect. A phenomenological model has been proposed to represent the concept of destabilization of polaron formation in the surface region of the nano grains. Resistivity and magnetoresistance data have been carefully analyzed employing different suitable models. Electrical third harmonic resistance has been measured to directly probe the electrical nonlinearity in the samples.