Super-heavy fermion material as metallic refrigerant for adiabatic demagnetization cooling

Abstract

Low-temperature refrigeration is of crucial importance in fundamental research of condensed matter physics, as the investigations of fascinating quantum phenomena, such as superconductivity, superfluidity and quantum criticality, often require refrigeration down to very low temperatures. Currently, cryogenic refrigerators with ${}^3$He gas are widely used for cooling below 1 Kelvin. However, usage of the gas is being increasingly difficult due to the current world-wide shortage. Therefore, it is important to consider alternative methods of refrigeration. Here, we show that a new type of refrigerant, super-heavy electron metal, YbCo${}_2$Zn${}_{20}$, can be used for adiabatic demagnetization refrigeration, which does not require 3He gas. A number of advantages includes much better metallic thermal conductivity compared to the conventional insulating refrigerants. We also demonstrate that the cooling performance is optimized in Yb${}_{1-x}$Sc${}_x$Co${}_2$Zn${}_{20}$ by partial Sc substitution with $x\sim$0.19. The substitution induces chemical pressure which drives the materials close to a zero-field quantum critical point. This leads to an additional enhancement of the magnetocaloric effect in low fields and low temperatures enabling final temperatures well below 100 mK. Such performance has up to now been restricted to insulators. Since nearly a century the same principle of using local magnetic moments has been applied for adiabatic demagnetization cooling. This study opens new possibilities of using itinerant magnetic moments for the cryogen-free refrigeration.

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Cited by in corpus (7)

• Frustrated magnet for adiabatic demagnetization cooling to milli-Kelvin temperatures
• Grüneisen parameter studies on heavy fermion quantum criticality
• Efficient adiabatic demagnetization refrigeration to below 50 mK with UHV compatible Ytterbium diphosphates $A$YbP${}_2$O${}_7$ ($A=$Na, K)
• Adiabatic demagnetization refrigeration to mK temperatures with the distorted square lattice magnet NaYbGeO${}_4$
• Utilizing frustration in Gd- and Yb-based oxides for milli-Kelvin adiabatic demagnetization refrigeration
• Metallic local-moment magnetocalorics as a route to cryogenic refrigeration
• Spin dynamics of the quantum dipolar magnet Yb${}_3$Ga${}_5$O${}_{12}$ in an external field