TEMPERATURE-DEPENDENCE OF THE MAGNETIC EXCITATION SPECTRUM OF DY2FE14B

We present inelastic magnetic neutron scattering spectra of polycrysta lline Dy2Fe14B measured between 2 and 650 K employing different time-o f-flight spectrometers. At the lowest temperatures we can identify in the magnetic excitation spectra the following features: (i) a dominant line at Delta = 12 meV with a shoulder at 11.1 meV, and (ii) two weak lines at 3.8 and 5.5 meV. The temperature dependence of the average p osition Delta of the dominant line follows roughly the temperature dep endence of the spontaneous magnetization of Y2Fe14B indicating that th e energy of this mode is substantially fixed by the molecular fields o f the surrounding Fe moments. Slight deviations, however, indicate tha t the Dy level spacing is not equidistant due to crystal field effects .