Suppression of charge-ordering and appearance of magnetoresistance in a spin-cluster glass manganite La0.3Ca0.7Mn0.8Cr0.2O3

TL;DR

This study investigates how Cr substitution suppresses charge ordering and induces large negative magnetoresistance in a manganite, revealing the role of spin clusters and magnetic phases at low temperatures.

Contribution

It demonstrates that Cr doping suppresses charge ordering and induces colossal magnetoresistance via spin-dependent hopping in a manganite.

Findings

Charge ordering is suppressed by Cr substitution.

Large negative magnetoresistance appears below 120 K in Cr-doped sample.

Ferromagnetic clusters coexist with spin-cluster glass phase at low temperatures.

Abstract

The magnetic properties of electron-doped manganite La0.3Ca0.7MnO3 and La0.3Ca0.7Mn0.8Cr0.2O3 polycrystalline samples prepared by sol-gel technique have been investigated between 5 and 300 K in magnetic fields ranging from 0 to 5 T. The transition at 260 K, attributed to charge ordering in La0.3Ca0.7MnO3, is completely suppressed in the Cr-substituted sample while the onset of a magnetic remanence followed by the appearance of a magnetic irreversibility at lower temperatures is observed in both samples. These features indicate that ferromagnetic clusters coexist with either an antiferromagnetic phase for La0.3Ca0.7MnO3 or a spin-cluster glass phase for La0.3Ca0.7Mn0.8Cr0.2O3 at the lowest temperatures. The exponential temperature dependence of the resistivity for the Cr-substituted sample is consistent with the small polaron hopping model for 120 K < T < 300 K, while the data are better described by Mott's hopping mechanism for T < 120 K. Whereas the parent compound La0.3Ca0.7MnO3 is known to show no magnetoresistance, a large negative magnetoresistance is observed in the La0.3Ca0.7Mn0.8Cr0.2O3 sample below 120 K. The appearance of the CMR is attributed to spin dependent hopping between spin clusters and/or between ferromagnetic domains.