Abstract
The spin-lattice relaxation time of naturally occurring in Ni(, a Haldane-gap system commonly known as NENP, has been measured as a function of temperature (T>4 K), magnetic field (H=3.46 and 7.56 T), and crystal orientation [a, b (the Ni chains), and c axes]. Using the established magnetic-field dependence of the gap and the materials parameters known for NENP, the general trends of the data can be reproduced by standard analysis with the assumption that the relaxation is governed by the processes at q=π. Most importantly, an unusual feature in the H(∥b)=7.56 T data can only be explained by using a temperature-dependent gap.
- Received 30 August 1996
DOI:https://doi.org/10.1103/PhysRevB.55.8079
©1997 American Physical Society