Inelastic Critical Neutron Scattering in Terbium

The critical neutron scattering above the Néel temperature TN in Tb has been measured using both double-axis and triple-axis spectrometry. The parameters of the magnetic susceptibility and the spin relaxation function have been deduced in the temperature range 0.005 ≲ (T-TN)/TN≲ 0.06. Both the inverse correlation range K1 and the long wavelength susceptibility X(Q) obey temperature power laws, with the exponents v = 0.66± 0.02 and γ = 1.33 ± 0.02, respectively. The results for the relaxation function show that thermodynamic slowing down of the spin fluctuations does occur in Tb when the temperature approaches the critical temperature. (author)