Sub-10 mK Refrigeration and Enhanced Magnetocaloric Effect

This research investigates future magnetic refrigerants with magnetocaloric effects enhanced by quantum phase transitions and their application in cryogenic systems. The motivation for this work is guided by the development of adiabatic demagnetization refrigeration (ADR) cells compatible with cryogen free systems [1]. Experiments with a prototype ADR cell achieved temperatures down to 2 mK and used a paramagnetic material, copper powder, as the refrigerant. The design of this cell supports using future materials of interacting spin systems as enhanced magnetocaloric refrigerants.

The thermodynamics for these interacting quantum spin materials with field induced quantum phase transitions are investigated using computational methods. This study focuses on spin-1 Heisenberg anti-ferromagnetic chains (HAFC) as a potential candidate for magnetic refrigeration [2]. Computational models such as minimally entangled typical thermal states (METTS), density matrix renormalization group (DMRG), and exact diagonalization (ED) provide a method for computing the optimal parameters of such a refrigerant [3]. This presentation reports on the explored thermodynamic phase space and presents some of the optimal characteristics for a correlated spin-1 refrigerant such as maximum entropy change and minimum temperature.

[1]    D.I. Bradley et al. J Low Temp Phys 57 (1984) 359.

[2]    T. Liu et al. Phys Rev Research 3 (2021) 033094.

[3]    E M Stoudenmire and Steven R White. New Journal of Physics 12 (2010) 055026.