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.
The structural, magnetic, and magnetocaloric effects (MCE) of Tm1-x
Er
x
CuAl (x = 0.25, 0.5, and 0.75) compounds were investigated. The compounds undergo a second-order phase transition originating from the ferromagnetic to paramagnetic transition around 3.2 K, 5 K and 6 K, respectively. The maximum magnetic entropy change (-ΔS
M
max
of Tm1-x
Er
x
CuAl (x = 0.25, 0.5, and 0.75) are 17.1 J kg-1K-1, 18.1 J kg-1K-1, and 17.5 J kg-1K-1 under the magnetic field change of 0-2 T, with corresponding RC of 131 J kg-1, 136 J kg-1 and 126 J kg-1, respectively. The increase of -ΔS
M
max
for Tm0.5Er0.5CuAl may be relevant to the change of magnetic moment distribution of Er and stress coming from element substitution. This work has provided several compounds that enrich the family of giant MCE materials in the cryogenic region.
The magnetic and magnetocaloric (MCE) of the amorphous RE
55Co30Al10Si5(RE = Er and Tm) ribbons were systematically investigated in this paper. Compounds with R = Er and Tm undergo a second order magnetic phase transition from ferromagnetic (FM) to paramagnetic (PM) around Curie temperature T
C ~ 9.3 K and 3 K, respectively. For Er55Co30Al10Si5 compound, an obvious magnetic hysteresis and thermal hysteresis were observed at low field below 6 K, possibly due to spin-glass behavior. Under the field change of 0-5 T, the maximum values of magnetic entropy change (−ΔS
M
max
) reach as high as 15.6 J/kg K and 15.7 J/kg K for Er55Co30Al10Si5 and Tm55Co30Al10Si5 compounds, corresponding refrigerant capacity (RC) values are estimated as 303 J/kg and 189 J/kg, respectively. The large MCE makes amorphous RE
55Co30Al10Si5 (RE = Er and Tm) alloys become very attractive magnetic refrigeration materials in the low-temperature region.
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