§1.导言近年来发现物质的顺磁性是关于获得极低温度(小于1°K)的重要物理问题的决定性因素。磁冷却方法具有特殊的价值。因为基于气体液化制冷方法,即利用汽化时的熵变在较低气压下效率变低,因此在一定时间内为了获得显著的熵变在技术上是不可能的,惯用的液—氦方法得到的最低温度是0.71K。这个方法在于抽出液—氦He~4上的蒸气、He~4是氦的最普 §1. Introduction The recent discovery of the paramagnetic nature of matter is a decisive factor in achieving important physical problems at very low temperatures (less than 1 ° K). Magnetic cooling method has a special value. Because the gas-based liquefaction refrigeration method, which utilizes the entropy change at vaporization, becomes less efficient at lower pressures, it is technically impossible to obtain significant entropy changes over time for the conventional liquid-helium process The minimum temperature is 0.71K. This method is to extract the liquid - helium He ~ 4 on the steam, He ~ 4 helium is the most common