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Peculiarities of magnetocaloric effect in manganites connected with magnetic heterogeneous stateстатья
- Авторы: Koroleva L.I., Morozov A.S.
- Журнал: American Journal of Modern Physics
- Том: 2
- Номер: 2
- Год издания: 2013
- Первая страница: 61
- Последняя страница: 67
- DOI: 10.11648/j.ajmp.20130202.15
- Аннотация: Magnetocaloric effect (MCE)or deltaT-effect was studied in La_(1-x)Sr_(x)MnO_3, Sm_0.55Sr_0.45MnO_3 and PrBaMn_2O_6 manganites. It has been found that the maximum value of MCE,measured by direct method, is far less than obtainable by computation from the change of the magnetic entropy in Curie temperature T_C. This phenomenon is explained by presence in them of the magnetic two-phase ferromagnetic (F) - antiferromagnetic (AF) state. So, in La_(1-x)Sr_(x)MnO_3 the negative contribution from AF portion of sample lowers MCE and displaces maximum on deltaT{T)-curve to the higher temperature than T_C on 20-40 K. Maximum on deltaT{T)-curve of Sm_0.55Sr_0.45MnO_3 is disposed near T_C=134 K in the cooling in the air single-crystal and ceramic samples. The cooling in oxygen of single-crystal restored the Mn-O-Mn broken connections,increases the volume of clusters with CE-type of AF order, results to that maximum on deltaT{T)-curve is disposed at Neel temperature T_N of this phase (243 K). Magnetic field applied to sample during deltaT-measurement transforms AF clusters into F state and the both types of clusters decompose at T_N.The PrBaMn_2O_6 manganite has two phase transition: paramagnetic-F at T_C=295 K and F-AF at T_N=231. Phase with spontaneoous magnetization obtaines the understated magnetic moment. Curve deltaT{T)has the wide maximum near T_C and the sharp nminimum near T_N with the small deltaT{T)-values in both extremes: 0,13 K and -0,2 K respectively.This is connected with presence of AF interactions in F phase and F interaction in AF phase.
- Добавил в систему: Королёва Людмила Ивановна