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

Abstract

Metallic super-heavy fermion compounds can be used for adiabatic demagnetization cooling to temperatures well below 0.1 K.

Thermomagnetic properties of very heavy fermions suitable for adiabatic demagnetisation refrigeration at low temperature

“…Within group (II) one can mention YbCu 4 Ni [8] which represents the family of compounds showing a C m /T | T →0 ≈ 7.5±0.5 J/mol K 2 'plateau' followed by a common power law above a change of regime at T = T * [11]. The compounds included in group (III) are characterized by showing NFL behavior, like (Yb,Sc)Co 2 Zn 20 [7] and CeNi 9−x T x (where T = Co [14] with x = 0.1, and T = Cu with x = 0.4 [15] respectively).…”

“…As expected, CMN shows a pure power law dependence because of the lack of conduction electrons. [7] and CeNi 8.9 Co 0.1 [14] are collected in Fig. 5 in a logarithmic T dependence.…”

“…Since C m /T is proportional to the density of excitations, the rich family of intermetallic heavy Fermions (HF) provides asignificant number of candidates for ADR applications. Among them are the recently synthesized Yb-intermetallic compounds [5][6][7][8][9][10], some of which have been tested as proper candidates for the proposed improvements because of their very large C m /T | T →0 values. These compounds were labeled as very HF (VHF) [11] because they largely exceed the values of classical HF [12].…”

“…All these paramagnetic materials do not order magnetically down to about 200 mK despite of their robust magnetic moments, providing large ∂M/∂T coefficients. As mentioned before, the entropy computed as: S m (T ) = C m /T dT is the basic parameter for the study of ARD processes because its thermal trajectory characterizes the efficiency and applicability of [6][7][8]. CMN salt (upper T scale) is included for comparison [3].…”

“…Horizontal arrow: cooling window ∆T . Shadowed triangle (top left) represents the heat absorbed Q abs by these materials in the process of thermal stabilization taking as reference the (Yb,Sc)Co2Zn20 system [7]. (b) Heats ratio RQ = Q abs /Q th as a function of magnetic field evaluated from Ti = 1 K. each cryo-material at the 'sub-Kelvin' range.…”