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 He-3. YbCu4Ni is known to exhibit a giant value of specific heat divided by temperature C/T & SIM; 7.5 J/K-2 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 YbCu4Ni ingots installed in a commercial He-4 refrigerator. The performance is consistent with that evaluated by our DC magnetization and specific heat measurements. Our study demonstrates the high performance of YbCu4Ni without precious metals as a magnetic refrigeration material with moderately high density of Yb atoms (& SIM; 0.02 Yb mol/cm(3)) and high thermal conductivity.