New NMR studies of in high-porosity aerogel reveal a phase transition from an -like to a -like phase on cooling. The evidence includes frequency shift and magnetic susceptibility data, and similar behavior is found in two quite different aerogel samples. The -like phase is stable only very near to but can be supercooled to below . This behavior has been seen clearly at 32- and 24-bar pressures, and the presence of negative frequency shifts suggests that an -like phase exists near at pressures as low as 12 bars in a magnetic field of 28.4 mT.
- Received 5 June 2000
- Published in the issue dated 4 September 2000
© 2000 The American Physical Society