Magnetic refrigeration down to 0.2 K by heavy fermion metal YbCu4Ni

Ytterbium-based heavy-fermion metals have recently attracted attention as magnetic refrigeration materials generating low-temperature environments below 1 K without using expensive ${}^3\mathrm{He}$ . ${\mathrm{YbCu}}_4\mathrm{Ni}$ is known to exhibit a giant value of specific heat divided by temperature $C/T\sim 7.5\mathrm{J}/{\mathrm{K}}^2\mathrm{mol}$ below 0.2 K, implying high potential of magnetic refrigeration. In this paper, we report magnetic refrigeration down to 0.2 K from the initial temperatures of 1.8 K by ${\mathrm{YbCu}}_4\mathrm{Ni}$ ingots installed in a commercial ${}^4\mathrm{He}$ refrigerator. The performance is consistent with that evaluated by our DC magnetization and specific heat measurements. Our study demonstrates the high performance of ${\mathrm{YbCu}}_4\mathrm{Ni}$ without precious metals as a magnetic refrigeration material with moderately high density of Yb atoms ($\sim 0.02\mathrm{Yb}\mathrm{mol}/{\mathrm{cm}}^3$ ) and high thermal conductivity.