resumo
Materials with strong magneto-volume coupling can present a coupled first-order magnetic and structural transition and a giant magnetocaloric effect. The trade-off of the resulting increased entropy change is hysteresis, and incomplete transition when the applied field is <2 T, implying that the full cooling capacity of the refrigerant is not harnessed. In this work, the behavior of the magnetic entropy change as a function of temperature is simulated, considering the Bean-Rodbell model, for various spin systems with Curie temperatures close to room temperature. Increasing magneto-volume coupling parameter (eta) results in higher entropy change peak value (Delta S-M(max)), together with a narrowing of entropy change function Delta S-M(T), limiting the working temperature range. Accordingly, cooling capacity behaves non-monotonously, reaching a peak value at eta(MAX), which departs from the tri-critical point as H increases up to 2 T. By tuning eta, the cooling capacity can be considerably larger than the uncoupled system (up to 15-40% for low applied fields). Such tuning can be accomplished experimentally through proper chemical substitution. A universal behavior of cooling capacity as a function of eta(MAX) underlines that the performance of magnetic refrigerant is optimized, by tuning magneto-volume coupling within the second order range, rather than the tri-critical region.
palavras-chave
PHASE-TRANSITION; 1ST-ORDER; HYSTERESIS
categoria
Physics
autores
Davarpanah, A; Belo, JH; Amaral, VS; Amaral, JS
nossos autores
Amin Davarpanah
Estudante de doutoramento
João Cunha de Sequeira Amaral
Investigador Auxiliar
João Silva
Bolseiro de pós-Doutoramento
Vitor Brás Sequeira Amaral
Professor CatedráticoProjectos
Projeto de Investigação Exploratória: João Amaral (IF/01089/2015)
agradecimentos
A. Davarpanah acknowledges his PhD grant from Fundacao para a Ciencia e Tecnologia (FCT) with reference SFRH/BD/103556/2014. J. Amaral would like to acknowledge FCT for his Researcher contract with reference: IF/01089/2015. The present study was developed in the scope of the Smart Green Homes Project [POCI-01-0247-FEDER-007678], a co-promotion between Bosch Termotecnologia S.A. and the University of Aveiro. It is financed by Portugal 2020 under the Competitiveness an Internationalization Operational Program, and by the European Regional Development Fund. This work was also developed within the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID /CTM /50011/2013), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement.