  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
(CH$_3$)$_4$NNi(NO$_2$)$_3$ (TMNIN) and NiCl$_2$-4SC(NH$_2$)$_2$ (DTN), where
DTN have significant low-$T$ refrigeration capacity while requiring only
moderate magnetic fields. The iMCE characteristics, including the adiabatic
temperature change $\Delta T_{\rm ad}$, isothermal entropy change $\Delta S$,
differential Gr\"uneisen 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.
