Performance improvement of a 4 K GM/magnetic hybrid refrigerator with a new magnetic regenerator

A hybrid refrigerator that combines the GM refrigeration effect with the magnetic refrigeration effect has been built before. Based on the hybrid refrigerator, a new magnetic regenerator filled with Pb, ErNi and EuTi_0.875Al_0.125O₃ has been constructed to improve the cooling performance of the hybrid refrigerator. Among the three regenerative materials, EuTi_0.875Al_0.125O₃ is a newly developed ferromagnetic material with high volumetric specific heat and large magnetocaloric effect below 5 K, which is better than the TmCuAl used in the previous regenerator. The numerical prediction shows that the new magnetic regenerator filled with EuTi_0.875Al_0.125O₃ could obtain a lower cooling temperature and a larger cooling power in the hybrid refrigerator. Then, the cooling performance of the new magnetic regenerator has been systematically studied by experimental tests. In the experiments, the minimum no-load temperature of the new magnetic regenerator could reach 2.48 K, which was much lower than the minimum no-load temperature of 3.5 K in the previous regenerator. Meanwhile, the cooling power of 0.652 W at 4.2 K was produced in the new magnetic regenerator, which was larger than the previous regenerator by 0.361 W, and the corresponding relative Carnot efficiency was 0.48 % at 4.2 K in the new magnetic regenerator.