Magnetic refrigeration in the temperature range from 10 K to room temperature: the ferromagnetic refrigerants |
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| Authors: | T. Hashimoto T. Numasawa M. Shino T. Okada |
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| Affiliation: | 1. TH, TN, MS are at the Department of Applied Physics, Faculty of Science, Tokyo Institute of Technology, Oh-okayama, Meguro, Tokyo, Japan;2. TO is at the Physics Laboratory, Japan Women''s University, Mejirodai, Bunkyo-ku Tokyo, Japan |
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| Abstract: | The criteria for selecting refrigerant materials for a magnetic refrigerator in the temperature range from 4.2 K to 300 K have been studied. First, by assuming the molecular field approximation, we calculated the magnetic entropy SM (T, H) of a typical 3-dimensional ferromagnetic substance near the Curie temperature as a function of temperature and magnetic field strength. In order to prove the validity of the above theoretical results, the magnetocaloric effects of Cr3Te4 and Gd near the room temperature have been investigated experimentally. Comparison between the calculated and experimental results confirms that they are in good agreement. Second, by using the Debye approximation, the temperature variation of the lattice entropy SL (T) as a function of the Debye temperature is clarified. Using the above SM (T, H) and SL (T), the temperature and magnetic field dependences of the calculated total entropy of several typical ferromagnets are obtained. In view of the above results we have discussed several criteria which should be satisfied by a magnetic refrigerant to be used near room temperature. |
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