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Antiferromagnetic LiErF4 has attracted extensive attention due to its dipolar interaction domination and quantum fluctuations action. In present work, the crystal structure, cryogenic magnetic properties, and magnetocaloric effect (MCE) of polycrystalline LiErF4 compound were investigated. Crystallographic study shows that the compound crystallizes in the tetragonal scheelite structure with I4 1 /a space group. It exhibits an antiferromagnetic (AFM) phase transition around 0.4 K, accompanied by a giant cryogenic MCE. At 1.3 K, the maximum values of magnetic entropy change are 24.3 J/kg K, 33.1 J/kg K, and 49.0 J/kg K under the low magnetic field change of 0-0.6 T, 0-1 T, and 0-2 T, respectively. The giant MCE observed above T N is probably due to the strong quantum fluctuations, which cause a large ratio of the unreleased magnetic entropy existing above the phase transition temperature. The outstanding low-field MCE below 2 K makes the LiErF4 compound an attractive candidate for the magnetic refrigeration at ultra-low temperature.

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The magnetic properties and magnetocaloric effect (MCE) in RCu2Si2 and RCu2Ge2 (R = Ho, Er) compounds have been investigated. All these compounds possess an antiferromagnetic (AFM)-paramagnetic (PM) transition around their respective Neel temperatures. The RCu2Si2 compounds undergo spin-glassy behavior above Neel temperature. Furthermore, a field-induced metamagnetic transition from AFM to ferromagnetic (FM) states is observed in these compounds. The calculated magnetic entropy changes show that all RCu2Si2 and RCu2Ge2 (R = Ho, Er) compounds, especially, ErCu2Si2 exhibits large MCEs with no thermal hysteresis and magnetic hysteresis loss. The value of −ΔSMmax reaches 22.8 J/Kg K for magnetic field changes from 0 to 5 T. In particular, for field changes of 1 and 2 T, the giant reversible magnetic entropy changes −ΔSMmax are 8.3 and 15.8 J/kg K at 2.5 K, which is lower than the boiling point of helium. The low-field giant magnetic entropy change, together with ignorable thermal hysteresis and field hysteresis loss of ErCu2Si2 compound is expected to have effective applications in low temperature magnetic refrigeration.

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Cryogenic refrigeration technology is gradually penetrating into increasing aspects in human life and industrial production. Magnetic refrigeration shows excellent application potential due to its high efficiency, good stability and environmental...

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