Complex Metallic Alloys for Applications in Magnetic Refrigeration

This manuscript presents our patent for a more effective magnetocaloric material based on Gd5Si2Ge2 as well as its method of production. The material has high refrigeration capacities and, with modifications to its composition, it is possible to control the temperature at which its magnetocaloric effect is the largest. This effect was achieved by modifying the stoichiometry of the starting composition. First, the Si or Ge is replaced with Fe in the starting composition; then, there is an additional heat treatment and quenching of the alloy. This produces a novel microstructure and a magnetocaloric material with an enhanced refrigeration capacity. Although the magnetocaloric effect is slightly reduced as a result of this process, the iron indirectly affects the microstructure and thereby reduces the hysteresis losses that occur during the first-order structural transformation. Hysteresis losses, of course, have a very detrimental effect on the refrigeration capacity. We observe that even a small amount of iron increases the refrigeration capacity up to 12%. Furthermore, by changing the amount of iron, we can alter the temperature at which the magnetocaloric effect is the largest. This then increases the temperature range over which this material can be applied. The patent covers the process for improving the usefulness of magnetocaloric Gd5Si2Ge2-based alloys as a working material for a magnetocaloricbased refrigerator. These refrigerators are energetically more efficient and environmentally less harmful than regular compressor-based refrigerators.