Magnetic refrigeration is to use the magnetocaloric effect of magnetic refrigeration materials, in the isothermal magnetization is to discharge energy to the outside world, demagnetization to absorb heat from the outside world, so as to achieve the purpose of refrigeration. When the magnetic material is magnetized, the order degree of magnetic moment increases, the magnetic entropy decreases, the temperature rises and the heat is released to the outside world; During demagnetization, the order degree of magnetic moment decreases, the magnetic entropy increases, the temperature decreases and the heat is absorbed from the outside.

According to the applied temperature range, magnetic refrigeration materials can be divided into three temperature regions: extremely low temperature, low temperature and high temperature. GGG single crystal can be applied to the extremely low temperature region below 20K, and successfully applied to the pre stage refrigeration of helium nitrogen liquefaction in he Ⅱ flow. Recently, the research on GGG refrigeration, which is jointly carried out by krystron and the Institute of physical and chemical technology, Chinese Academy of Sciences, has achieved good results: at present, the minimum temperature can reach 540 MK.

Compared with traditional refrigeration technology, magnetic refrigeration technology has the advantages of high efficiency and energy saving, no pollution, stable and reliable operation, and will have broad application prospects in daily life, industrial production, agriculture, military, aerospace and other fields in the future.