Magnetic entropy change of Pr1-xCaxMnO3 manganites (0.2 <= x <= 0.95)

• Tipo: Artigo em Revista Científica Internacional
• Data: 2005

Autores

Reis, Mário Souza (Autor) Outra; Amaral, V. S. (Autor) Outra; Araújo, João Pedro (Autor) FCUP; Tavares, Pedro B. (Autor) Outra; Gomes, Angelo M S (Autor) Outra; Oliveira, Ivan S. (Autor) Outra

Revista

Título: Physical Review B - Condensed Matter and Materials Physics

Vol. 71

ISSN: 1098-0121

Editora: American Physical Society

Indexação

ISI Web of Knowledge - 80 Citações

Scopus - 88 Citações

Outras Informações

ID Authenticus: P-000-44H

DOI: 10.1103/physrevb.71.144413

Abstract (EN): In the present work we analyze the magnetic entropy change Delta S-M of the Pr1-xCaxMnO3 manganites, for a wide range of Ca concentrations (0.20 <= x <= 0.95). The results for the samples with 0.20 < x <= 0.30 present the usual behavior expected for ferromagnetic systems, peaking at the Curie temperature T-C. In contrast, for the charge-ordered antiferromagnetic samples (0.30 < x < 0.90), an anomalous magnetic entropy change starts around the charge-ordering temperature T-CO, persisting for lower values of temperature. This effect is associated to a positive contribution to the magnetic entropy change due to the charge-ordering Delta S-CO, which is superimposed to the negative contribution from the spin-ordering Delta S-spin; that is described using a mean-field approximation. Supposing these contributions, we could also appraise Delta S-CO(max) as a function of Ca content, which vanishes for the limits x similar to 0.30 and 0.90 and presents a deep minimum around x similar to 0.50, with two maxima at x similar to 0.35 and 0.65. We conclude that for x>0.65 only the magnetic order governs the charge ordering, contrarily to x < 0.65, where there are more than one mechanism ruling the charge ordering. Moreover, for the samples with phase coexistence (0.30 < x <= 0.40), we found extremely large values for the magnetic entropy change at low temperatures. Finally, for x>0.90, we found usual magnetic entropy change curves, peaking at the Neel temperature T-N.

Idioma: Inglês

Tipo (Avaliação Docente): Científica

Nº de páginas: 8