Large magnetocaloric effect and adiabatic demagnetization refrigeration with YbPt₂Sn

摘要

Adiabatic demagnetization is currently gaining strong interest in searching for alternatives to 3He-based refrigeration techniques for achieving temperatures below 2?K. The main reasons for that are the recent shortage and high price of the rare helium isotope 3He. Here we report the discovery of a large magnetocaloric effect in the intermetallic compound YbPt₂Sn, which allows adiabatic demagnetization cooling from 2?K down to 0.2?K. We demonstrate this with a home-made refrigerator. Other materials, for example, paramagnetic salts, are commonly used for the same purpose but none of them is metallic, a severe limitation for low-temperature applications. YbPt₂Sn is a good metal with an extremely rare weak magnetic coupling between the Yb atoms, which prevents them from ordering above 0.25?K, leaving enough entropy free for use in adiabatic demagnetization cooling. The large volumetric entropy capacity of YbPt₂Sn guarantees also a good cooling power.