Specific heat and magnetic order in LaMnO/sub 3+[delta]/

Abstract

Magnetic and specific-heat measurements are performed in three different samples of LaMnO₃₊[delta], with δ = 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 δ = 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, δ = 0.26, the disorder is sufficient to suppress even short-range ferromagnetic order and yield a spin-glass-like state.