Adiabatic nuclear demagnetization: two sophisticated experiments

After a brief introduction to nuclear demagnetization, two recent experiments in the author's laboratory are described. Gyroscopic measurements on superfluid sup(3)He-B in a rotating nuclear refrigerator demonstrated undiminished persistent currents for 48 hours and revealed a vortex-core phase transition, manifested by an abrupt change in the critical flow velocity and a large latent heat. Experiments in a cascade nuclear demagnetization cryostat, capable of cooling copper nuclei to 30 nanokelvins, established a magnetic fields vs. entropy diagrams, which shows that the nuclear spin system of copper has three different antiferromagnetic phases below 0.27 mT. In zero field the transition temperature is 60 nK. (author)