Colossal electroresistance in ferromagnetic insulating state of single crystal Nd$_0.7$Pb$_0.3$MnO$_3$

TL;DR

This study reports colossal electroresistance in the ferromagnetic insulating phase of Nd0.7Pb0.3MnO3, showing large resistivity changes with current independent of magnetoresistance, revealing distinct underlying mechanisms.

Contribution

It demonstrates the occurrence of colossal electroresistance in a ferromagnetic insulating state, distinct from metallic and charge-ordered phases, and highlights the decoupling of electroresistance and magnetoresistance mechanisms.

Findings

Colossal electroresistance (~100%) observed below 130 K.

Resistivity exhibits negative differential resistivity at low temperatures.

Magnetoresistance remains small (<20%) despite large electroresistance.

Abstract

Colossal electroresistance (CER) has been observed in the ferromagnetic insulating (FMI) state of a manganite. Notably, the CER in the FMI state occurs in the absence of magnetoresistance (MR). Measurements of electroresistance (ER) and current induced resistivity switching have been performed in the ferromagnetic insulating state of a single crystal manganite of composition Nd$_0.7$Pb$_0.3$MnO$_3$ (NPMO30). The sample has a paramagnetic to ferromagnetic (Curie) transition temperature, Tc = 150 K and the ferromagnetic insulating state is realized for temperatures, T <~ 130 K. The colossal electroresistance, arising from a strongly nonlinear dependence of resistivity ($\rho$) on current density (j), attains a large value ($\approx 100%$) in the ferromagnetic insulating state. The severity of this nonlinear behavior of resistivity at high current densities is progressively enhanced with decreasing temperature, resulting ultimately, in a regime of negative differential resistivity (NDR, d$\rho$/dj < 0) for temperatures <~ 25 K. Concomitant with the build-up of the ER however, is a collapse of the MR to a small value (< 20%) even in magnetic field, H = 7 T. This demonstrates that the mechanisms that give rise to ER and MR are effectively decoupled in the ferromagnetic insulating phase of manganites. We establish that, the behavior of ferromagnetic insulating phase is distinct from the ferromagnetic metallic (FMM) phase as well as the charge ordered insulating (COI) phase, which are the two commonly realized ground state phases of manganites.