Specific heat and magnetic order in LaMnO_{3+\delta}

TL;DR

This study investigates how varying levels of oxygen vacancies in LaMnO_{3+ extdelta} affect its magnetic phases and specific heat, revealing transitions from ferromagnetic to spin-glass states due to disorder.

Contribution

It provides detailed experimental insights into the impact of disorder on magnetic and thermal properties in LaMnO_{3+ extdelta}, highlighting new phenomena such as cluster-glass and spin-glass states.

Findings

Two-step magnetic transition in samples with .11 and 0.15 ; ferromagnetic to cluster-glass.

Large linear term and spin-wave contributions in specific heat.

Suppression of ferromagnetic order in .26 sample, leading to spin-glass-like state.

Abstract

Magnetic and specific-heat measurements are performed in three different samples of LaMnO_{3+\delta}, with \delta=0.11, 0.15 and 0.26, presenting important disorder effects, such as carrier localization, due to high amounts of La and Mn vacancies. For the samples with \delta =0.11 and 0.15, magnetic measurements show signatures of a two-step transition: as the temperature is lowered, the system enters a ferromagnetic phase followed by a disorder-induced cluster-glass state. Spin-wave-like contributions and an unexpected large linear term are observed in the specific heat as a function of temperature. In the sample with the highest vacancy content, \delta=0.26, the disorder is sufficient to suppress even short-range ferromagnetic order and yield a spin-glass-like state.