Specific heat and magnetic order in LaMnO3+delta

Magnetic and specific-heat measurements are performed in three different sa mples of LaMnO3+delta, with delta =0.11, 0.15, and 0.26, presenting importa nt disorder effects, such as carrier localization, due to high amounts of L a and Mn vacancies. For the samples with delta = 0.11 and 0.15, magnetic me asurements show signatures of a two-step transition: as the temperature is lowered, the system enters a ferromagnetic phase followed by a disorder-ind uced cluster-glass state. Spin-wave-like contributions and an unexpected la rge linear term are observed in the specific heat as a function of temperat ure. In the sample with the highest vacancy content, delta = 0.26, the diso rder is sufficient to suppress even short-range ferromagnetic order and yie ld a spin-glass-like state. [S0163-1829(99)12041-1].