Abstract
The longitudinal, transverse, and paramagnetic spin fluctuations in Ni have been measured near by means of polarized neutron scattering in the momentum range 0.06<q<0.18 A. In transverse scans, spin-wave peaks at = appear as expected from previous measurements performed with unpolarized neutrons. The longitudinal fluctuations are quasielastic, in agreement with predictions of a recent mode-mode coupling theory and renormalization-group theory. The data indicate that the longitudinal dynamical scaling function is smaller than 1 just below . The scaling function for the paramagnetic scattering is shown to be in agreement with the Résibois-Piette scaling function for energy scales up to . The measured field dependence of the scattering is rather weak, indicating that the internal fields H are rather large. Therefore it was impossible to observe the divergence of (q→0) that is predicted for the isotropic Heisenberg model in three dimensions. In contrast, we found (q→0)∝(1-T/, which also appears to be a result of the internal fields. The q dependence of is Lorentzian-like. The T dependence of the correlation length indicates critical behavior. These features closely resemble the behavior of the paramagnetic fluctuations, and they are in agreement with results obtained with use of ε-expansion techniques.
- Received 20 August 1990
DOI:https://doi.org/10.1103/PhysRevB.43.575
©1991 American Physical Society