Giant magnetocaloric effect of K3Gd5(PO4)6 compound at ultra-low temperature

Abstract

Magnetic refrigerants possess large low fields magnetic entropy changes (-ΔSM) in sub-kelvin temperature region are urgently desired for adiabatic demagnetization refrigeration (ADR). Here, we report the large low fields magnetocaloric effect of K3Gd5(PO4)6, a phosphate compound based on Gadolinium, which experiences an antiferromagnetic transition at a Néel temperature of 0.64 K, while the dominant magnetic interaction is ferromagnetic. Under the field change of 0-1 T, the maximum values of magnetic entropy change () is 25.4 J kg−1 K−1 below 2 K is observed. Upon quasi-adiabatic demagnetization measurement, the quasi-adiabatic demagnetization curves show a dip, which lead to the lowest temperature occurred at nonzero applied field. Furthermore, the temperature as low as 510 mK is obtained with an initial condition of 4 T and 4 K, much larger than the temperature GGG can reach at the same initial condition (880 mK). The above results make K3Gd5(PO4)6 a promising magnetic refrigerant at sub-kelvin temperature region.