Specific heat, magnetocaloric effect and phase diagram of La1-xSrxMnO3 system for 0 ≤ x ≤ 1

Andrzej Szewczyk 1Maria Gutowska 1Bogdan Dabrowski 2

1. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
2. Northern Illinois University (NIU), Faraday Hall W216, De Kalb, Il 60115, United States

Abstract

Majority of research of La1-xSrxMnO3 manganites was performed for x < 0.4 compositions. Only a few papers (~5) described properties of the 0.6 < x ≤ 1.0 samples. This was caused by an inherent difficulty in synthesizing samples with x > 0.5. In the present studies, the phase diagram for the whole range of compositions (0 ≤ x ≤ 1) was investigated by means of the specific heat measurements, that were performed for 11 selected compositions, over the temperature range 2-390 K, in magnetic field up to 9 T. As a result, (1) two controversies concerning the phase diagram have been clarified, i.e., it was shown that the order of the Jahn-Teller transition does not depend on x and that the phase transition occurring below the Curie temperature for the 0.155 ≤ x ≤ 0.17 samples is the Jahn-Teller transition, not a charge ordering one. (2) The ferromagnet-paramagnet, antiferromagnet-paramagnet, and antiferromagnet-ferromagnet transitions have been thoroughly studied. It was evidenced that the shape of the specific heat anomaly and the kind of critical behavior of the specific heat at the antiferromagnet-paramagnet phase transition strongly depended on the type of the antiferromagnetic configuration (A, C, and G). The temperature of the first order antiferromagnet-ferromagnet transition occurring in the x = 0.55 composition was found to be strongly lowered by the magnetic field (by ~33 K for 9 T). (3) Two parameters characterizing magnetocaloric effect, i.e., the change of temperature of an adiabatically isolated sample and the change of entropy of a sample under isothermal conditions, induced by the change of magnetic field, have been determined. The values of these parameters, allowing to assess applicability of the studied material for magnetic refrigeration, suggest that the magnetocaloric effect in (La,Sr)MnO3 is substantial but not outstanding in comparison with other refrigerant materials.

 

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Presentation: Poster at E-MRS Fall Meeting 2006, Symposium K, by Andrzej Szewczyk
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-05-15 15:37
Revised:   2009-06-07 00:44