Experimental study on a single-stage adiabatic demagnetization refrigerator with Chromium Potassium Alum

As an excellent paramagnetic material with low Curie temperature, Chromium Potassium Alum (CPA) is commonly used in the adiabatic demagnetization refrigerator (ADR) to achieve extremely low temperatures. A typical ADR consists of many components, such as a salt pill, a superconducting magnet, a heat switch, etc. An experimental system was built to test the performance of a single-stage ADR we designed. A two-stage GM refrigerator was used to provide ADR with a low-temperature environment of less than 4 K. A superfluid helium bath was connected to the ADR, via a mechanical heat switch. In the experiment, the CPA salt pill can be pre-cooled to 1.35 K by the superfluid helium bath. A superconductor power supply is used to magnetize and demagnetize the crystal. After applying a 1 T magnetic field, the single-stage ADR can obtain a minimum temperature of 318.5 mK.