Nuclear Cooling in PrCu6

Nuclear adiabatic demagnetization experiments have been performed in the Van Vleck paramagnet PrCu6 in order to determine the very-low-temperature nuclear magnetic properties of this material and to test its efficiency as a very low-temperature refrigerator. It is found that a temperature of 2.7 mK can be reached from an initial temperature of 40 mK and an initial field of 20 kOe. Susceptibility and specific heat measurements above 2.7 mK indicate the presence of both nuclear quadrupole and exchange interactions. The transition to an antiferromagnetically ordered state among the Pr nuclei is expected to occur below 2.7mK.