Giant cryogenic magnetocaloric effect in mineral of gaudefroyite: Direct and indirect measurements

The magnetic and magnetocaloric properties of gaudefroyite minerals were studied. The magnetocaloric effect was investigated by direct and indirect methods in the temperature range 4.2–40 K and magnetic field up to 10 T. The magnetization was measured in a low magnetic field (200 Oe) with zero-field cooled and field cooling protocol and previous observation of typical spin glass behavior was confirmed. The giant magnetic entropy changes with anisotropic behavior and maximums |ΔS_m|= 17 J kg⁻¹ K⁻¹ (H||c) at 18 K and |ΔS_m|= 20 J kg⁻¹ K⁻¹ (H||ab) at 12 K at an applied magnetic field 10 T were observed. The direct measurements of the magnetocaloric effect demonstrated the maximum of adiabatic temperature changes of ΔT_ad = 11 K at a magnetic field change of 10 T (H||ab) at 11.5 K. Obtained values of magnetocaloric parameters for the mineral of gaudefroyite are comparable to promising materials for magnetic crycooling technologies (for example, hydrogen (LH₂) liquefaction) and have an advantage for the absence of rare-earth elements in the gaudefroyite.