High-resolution specific-heat and magnetocaloric-effect measurements have been utilized to complement the magnetic phase diagram of the hexagonal antiferromagnet in fields up to 14 T aligned perpendicular to the c axis. The recently found additional incommensurate phase induced by thermal fluctuations could be resolved completely. It appears at about 4 T in a narrow temperature range, with a maximum width of only and narrows towards higher fields extending up to Within the low-temperature incommensurate phase, the magnetocaloric-effect data confirm another phase transition that may be explained by quantum fluctuations.
- Received 21 August 2001
©2001 American Physical Society