Significant Inverse Magnetocaloric Effect induced by Quantum Criticality

Abstract

The criticality-enhanced magnetocaloric effect (MCE) near a field-induced quantum critical point (QCP) in the spin systems constitutes a very promising and highly tunable alternative to conventional adiabatic demagnetization refrigeration. Strong fluctuations in the low-T quantum critical regime can give rise to large thermal entropy change and thus significant refrigeration capacity when approaching the QCP. In this work, we show there exists a significant inverse MCE (iMCE) in the spin-1 quantum chain materials (CH3)4NNi(NO2)3 (TMNIN) and NiCl2-4SC(NH2)2 (DTN), where DTN have significant low-T refrigeration capacity while requiring only moderate magnetic fields. The iMCE characteristics, including the adiabatic temperature change ∆T ad , isothermal entropy change ∆S, differential Grüneisen parameter, and entropy change rate, are simulated by thermal many-body calculations. The cooling performance, i.e., the efficiency factor and hold time, of the two compounds are also discussed. Through optimizing the iMCE properties with machine learning techniques, we conclude that the DTN locates near the optimal parameter regime, and constitutes a very promising versatile quantum magnetic coolant. We also provide guide for designing highly efficient and cryofree quantum magnetic refrigeration for space applications and quantum computers.