Frustrated Metastable Behavior of Magnetic and Transport Properties in Charge Ordered La1-xCaxMnO3+d Manganites

TL;DR

This study investigates how repeated thermal cycling induces irreversible changes in the magnetic and transport properties of La1-xCaxMnO3 manganites near charge ordering, revealing metastable states influenced by microstructural strains and oxygen non-stoichiometry.

Contribution

It demonstrates the role of thermal cycling and oxygen non-stoichiometry in creating and relaxing metastable magnetic and electronic states in charge-ordered manganites, highlighting microstructural effects.

Findings

Thermal cycling causes irreversible transformation from ferromagnetic metallic to insulating states.

Metastable states relax over time and can be revived by high-temperature treatment.

Magnetic fields can inhibit the thermal cycling effects.

Abstract

We have studied the effect of metastable, irreversibility induced by repeated thermal cycles on the electric transport and magnetization of polycrystalline samples of La1-xCaxMnO3 (0.48\leq x \leq 0.55) close to charge ordering. With time and thermal cycling (T<300 K) there is an irreversible transformation of the low-temperature phase from a partially ferromagnetic and metallic to one that is less ferromagnetic and highly resistive for the composition close to charge ordering (x=050 and 0.52). Irrespective of the actual ground state of the compound, the effect of thermal cycling is towards an increase of the amount of the insulating phase. We have observed the magnetic relaxation in the metastable state and also the revival of the metastable state (in a relaxed sample) due to high temperature thermal treatment. We observed changes in the resistivity and magnetization as the revived metastable state is cycled. The time changes in the magnetization are logarithmic in general and activation energies are consistent with those expected for electron transfer between Mn ions. Changes induced by thermal cycling can be inhibited by applying magnetic field. These results suggest that oxygen non-stoichiometry results in mechanical strains in this two-phase system, leading to the development of frustrated metastable states which relax towards the more stable charge-ordered and antiferromagnetic microdomains. Our results also suggest that the growth and coexistence of phases gives rise to microstructural tracks and strain accommodation, producing the observed irreversibility.