Temperature dependence of the low-frequency magnetic excitations in USb.

Abstract

The low-frequency inelastic magnetic response in the type-I fcc antiferromagnet uranium antimonide (USb) has been studied by inelastic neutron scattering in the temperature range from 12 K (0.06${T}_{N}$) up to 320 K (1.51${T}_{N}$). At the lowest temperature, the lowest-lying magnetic excitations in USb are a well-defined, dispersive, spin-wave branch. In the temperature range up to 100 K, the principal effect of temperature on this spin-wave branch is to increase the frequencies of the spin waves. However, in the temperature range from 100 to 160 K, these spin waves become progressively damped until at 160 K (0.75${T}_{N}$) they have collapsed into broad inelastic scattering that peaks only at zero frequency. This scattering is a precursor to the critical scattering which develops around the N\'eel temperature of ${T}_{N}$=212.30\ifmmode\pm\else\textpm\fi{}0.05 K. The critical scattering both above and below the N\'eel temperature has been measured and the critical exponents and amplitude ratios associated with the inverse correlation lengths, the staggered susceptibility, and the characteristic frequency have been determined. These exponents are discussed in terms of a system in a d=3, n=3 universality class. In the temperature range above ${T}_{N}$, precursor critical scattering has been observed up to 320 K (\ensuremath{\sim}1.5${T}_{N}$).