Metallic local-moment magnetocalorics as a route to cryogenic refrigeration

TL;DR

This paper introduces YbNi1.6Sn, a metallic magnetocaloric material with high entropy at very low temperatures, offering a durable and efficient alternative for cryogenic refrigeration below 120 mK, overcoming limitations of traditional salts.

Contribution

The study presents YbNi1.6Sn as a novel metallic magnetocaloric with superior low-temperature properties and explains its effectiveness through its unique magnetic interactions.

Findings

YbNi1.6Sn retains high entropy below 100 mK.

Demagnetisation tests show effective cooling below 120 mK.

YbNi1.6Sn operates in the local moment limit with minimal Kondo and RKKY interactions.

Abstract

Commercial adiabatic demagnetisation refrigerators still employ the same hydrated salts that were first introduced over 85 years ago. The inherent limitations of these insulating magnetocalorics - poor thermal conductivity at sub-Kelvin temperatures, low entropy density, corrosiveness - can be overcome by a new generation of rare-earth based metallic magnetocalorics. Here, we present the metallic magnetocaloric YbNi1.6 Sn as an attractive alternative to conventional refrigerants. YbNi1.6Sn retains high entropy into the 100 mK regime and avoids the noble metal constituents of alternative refrigerants. Demagnetisation tests demonstrate that YbNi1.6Sn enables economical and durable alternatives to traditional cooling devices for temperatures reaching below 120 mK. We find that the magnetocaloric properties of this material are facilitated by unusually small Kondo and RKKY interactions, which position YbNi1.6Sn in the extreme local moment limit on the generalised Kondo lattice phase diagram.