Temperature dependence of the magnetic excitations in gadolinium

The magnetic excitation spectra of Gd were measured out to the zone boundaries in the 〈h00〉 and 〈00l〉 directions over the temperature range from 9 to 320 K. The 〈h00〉 data were not analyzed because of technical complications, but the 〈00l〉 data are described remarkably well over the entire q and T range of the experiments by a damped-harmonic-oscillator form for the spectral weight function. The 〈00l〉 data were parametrized and placed on an absolute basis by an internal calibration using the energy-integrated intensities of the low-temperature spin waves. This parametrization and calibration of the data provide a description of both the static and dynamic spin correlations over this temperature range. Spin-wave peaks are not observed above $T_c$ in the 〈00l〉 direction. We attribute this result to the low spin-excitation energies relative to $k_B$ $T_c$ in this direction.