Super-heavy electron material as metallic refrigerant for adiabatic demagnetization cooling.
Low-temperature refrigeration is of crucial importance in fundamental research of condensed matter physics, because 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 K. However, usage of the gas has been increasingly difficult because of the current worldwide shortage. Therefore, it is important to consider alternative methods of refrigeration. We show that a new type of refrigerant, the super-heavy electron metal YbCo2Zn20, can be used for adiabatic demagnetization refrigeration, which does not require (3)He gas. This method has a number of advantages, including much better metallic thermal conductivity compared to the conventional insulating refrigerants. We also demonstrate that the cooling performance is optimized in Yb1-x Sc x Co2Zn20 by partial Sc substitution, with x ~ 0.19. The substitution induces chemical pressure that drives the materials 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. This performance has, up to now, been restricted to insulators. For 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 cryogen-free refrigeration.
I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany.; Department of Physics, Kyoto University, Kyoto 606-8502, Japan.; Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany.
Yoshifumi
Y
Tokiwa
I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany.
Boy
0000-0001-6716-530X
B
Piening
I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany.
Hirale S
0000-0003-4415-0855
HS
Jeevan
Ames Laboratory, U.S. Department of Energy, and Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA.
Sergey L
SL
Bud'ko
Ames Laboratory, U.S. Department of Energy, and Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA.
Paul C
PC
Canfield
I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany.; Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany.
Philipp
P
Gegenwart
D003080:Cold Temperature; D004553:Electric Conductivity; D004579:Electron Transport; D004583:Electrons; D008280:Magnetics; D008670:Metals / Q000737:chemistry*; D044367:Phase Transition; D011789:Quantum Theory; D012034:Refrigeration / Q000295:instrumentation / Q000379:methods*
D008670:Metals
Adiabatic demagnetization refrigeration; heavy fermion; quantum critical point