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Transition-metal-based magnetic refrigerants for room-temperature applications

Abstract

Magnetic refrigeration techniques based on the magnetocaloric effect (MCE) have recently been demonstrated as a promising alternative to conventional vapour-cycle refrigeration1. In a material displaying the MCE, the alignment of randomly oriented magnetic moments by an external magnetic field results in heating. This heat can then be removed from the MCE material to the ambient atmosphere by heat transfer. If the magnetic field is subsequently turned off, the magnetic moments randomize again, which leads to cooling of the material below the ambient temperature. Here we report the discovery of a large magnetic entropy change in MnFeP0.45As0.55, a material that has a Curie temperature of about 300 K and which allows magnetic refrigeration at room temperature. The magnetic entropy changes reach values of 14.5 J K-1 kg-1 and 18 J K-1 kg-1 for field changes of 2 T and 5 T, respectively. The so-called giant-MCE material Gd5Ge2Si2 (ref. 2) displays similar entropy changes, but can only be used below room temperature. The refrigerant capacity of our material is also significantly greater than that of Gd (ref. 3). The large entropy change is attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field.

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Figure 1: Schematic representation of a magnetic-refrigeration cycle, which transports heat from the heat load to its surroundings.
Figure 2: Temperature dependence of the magnetization M for MnFeP0.45As0.55 and Gd.
Figure 3: Magnetic entropy changes of MnFeP0.45As0.55, Gd and Gd5Ge2Si2.

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Acknowledgements

We thank A.J. Riemersma for preparation of graphs. Part of this work was performed within the scientific exchange program between the Netherlands and China. This work was financially supported by the Dutch Technology Foundation STW.

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Correspondence to E. Brück.

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Tegus, O., Brück, E., Buschow, K. et al. Transition-metal-based magnetic refrigerants for room-temperature applications. Nature 415, 150–152 (2002). https://doi.org/10.1038/415150a

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