Quantum spin liquid candidate as superior refrigerant in cascade demagnetization cooling

The quantum spin liquid (QSL) states with no long-range magnetic order even down to zero temperature have recently raised intensive research interest. Here we propose that the spin frustration characteristic of the QSL candidates also make them superior magnetocaloric materials that exhibit prominent cooling effect, especially near the quantum critical points. By simulating the highly frustrated kagome and triangular lattice models, we reveal a significant magnetothermal pumping effect when combing quantum magnets with paramagnetic salts, which can be exploited to design a high-performance cascade demagnetization refrigerator. Moreover, with realistic magnetic compounds YbAlO3 and Na2BaCo(PO4)2, we find a giant enhancement in the cooling capacity characterized by a great increment rate, e.g., more than 200% when working between 3 K heat sink and 30 mK load. Our work thus paves a promising and viable way for the quantum spin cooling to promote the helium-free refrigeration useful in space applications and quantum technologies.