| Abstrakt: |
After a brief introduction to nuclear demagnetization, two recent Otaniemi experiments are described. Gyroscopic measurements on superfluid 3He-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, have established a magnetic field vs. entropy diagram, which shows that the nuclear spin system of copper has three antiferromagnetic phases below 0.27 mT; in zero field the transition temperature is 60 nK. |
