The field dependence of the inelastic neutron scattering from the reentrant spin glass (RSG) Fe70.4Al29.6 is investigated below TC. In the intermediate paramagnetic phase 100 KTinvc $\simeq$200 K spin waves are induced in an applied field. The peaks broaden rapidly with increasing q and decreasing temperature. Remarkably these excitations exhibit a dispersion curve with a ``negative'' slope. In a field of 10 kOe the energy gap corresponds to a Zeeman splitting g$\mu$BH$\simeq$0.11 meV. In the spin-glass phase at 10 K no inelastic scattering is observed in a field, although the sample is close to saturation. The results are interpreted in terms of a field-induced dispersion, which has been observed recently in a diluted random antiferromagnet.     «

The field dependence of the inelastic neutron scattering from the reentrant spin glass (RSG) Fe70.4Al29.6 is investigated below TC. In the intermediate paramagnetic phase 100 KTinvc $\simeq$200 K spin waves are induced in an applied field. The peaks broaden rapidly with increasing q and decreasing temperature. Remarkably these excitations exhibit a dispersion curve with a ``negative'' slope. In a field of 10 kOe the energy gap corresponds to a Zeeman splitting g$\mu$BH$\simeq$0.11 meV. In the sp...     »