Provenzano Virgil, Shapiro Alexander J, Shull Robert D
Magnetic Materials Group, NIST, 100 Bureau Drive, MS-8552, Gaithersburg, Maryland 20899, USA.
Nature. 2004 Jun 24;429(6994):853-7. doi: 10.1038/nature02657.
The magnetocaloric effect is the change in temperature of a material as a result of the alignment of its magnetic spins that occurs on exposure to an external magnetic field. The phenomenon forms the basis for magnetic refrigeration, a concept purported to be more efficient and environmentally friendly than conventional refrigeration systems. In 1997, a 'giant' magnetocaloric effect, between 270 K and 300 K, was reported in Gd5Ge2Si2, demonstrating its potential as a near-room-temperature magnetic refrigerant. However, large hysteretic losses (which make magnetic refrigeration less efficient) occur in the same temperature range. Here we report the reduction (by more than 90 per cent) of these hysteretic losses by alloying the compound with a small amount of iron. This has the additional benefit of shifting the magnetic entropy change peak (a measure of the refrigerator's optimal operating temperature) from 275 K to 305 K, and broadening its width. Although the addition of iron does not significantly affect the refrigerant capacity of the material, a greater net capacity is obtained for the iron-containing alloy when the hysteresis losses are accounted for. The iron-containing alloy is thus a much-improved magnetic refrigerant for near-room-temperature applications.
磁热效应是指材料在受到外部磁场作用时，其磁自旋排列发生变化而导致的温度改变。这一现象构成了磁制冷的基础，磁制冷这一概念据称比传统制冷系统更高效且更环保。1997年，在Gd5Ge2Si2中报道了在270 K至300 K之间的“巨大”磁热效应，证明了其作为近室温磁制冷剂的潜力。然而，在相同温度范围内会出现较大的磁滞损耗（这使得磁制冷效率降低）。在此，我们报告通过将该化合物与少量铁合金化，可使这些磁滞损耗降低（超过90%）。这还有额外的好处，即将磁熵变峰值（衡量冰箱最佳工作温度的指标）从275 K移至305 K，并拓宽其宽度。尽管添加铁对材料的制冷能力没有显著影响，但在考虑磁滞损耗时，含铁合金获得了更大的净制冷量。因此，含铁合金是一种用于近室温应用的显著改进的磁制冷剂。
