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Magnetic excitations in an intermetallic compound MnSi have been studied by neutron scattering. At 5 K in a magnetic field of 10 kOe, well-defined spin-wave excitations have been observed 0 belo~2.5 meV. The dispersion relation is almost isotropic and is hm"(meV) =0.13+52@2 (A 2) in the [100] direction, Above 3 meV, the excitation linewidth increases substantially, suggesting that the dispersion relation merges into the Stoner continuum. The Stoner excitations, which extend over almost all of the Brillouin zone, show a broad peak on the extension of the spin-wave dispersion relation. The spin-wave excitation renormalizes with increasing temperature and collapses into critical scattering above 40 K. On the other hand, the excitation in the Stoner continuum is aft'ected little by temperature; the excitations are qualitatively the same at T/T~=10 as at 5 K. The Stoner boundary energy decreases with increasing temperature. The results provide us with the first example of magnetic excitations in a weak itinerant ferromagnet.

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We report inelastic neutron scattering experiments performed to investigate the low energy magnetic excitations on single crystals of the heavy-fermion superconductor PrOs(4)Sb(12). The observed excitation clearly softens at a wave vector Q=(1,0,0), which is the same as the modulation vector of the field-induced antiferro-quadrupolar ordering, and its intensity at Q=(1,0,0) is smaller than that around the zone center. This result directly evidences that this excitonic behavior is derived mainly from nonmagnetic quadrupolar interactions. Furthermore, the narrowing of the linewidths of the excitations below the superconducting transition temperature indicates the close connection between the superconductivity and the excitons.

Inelastic neutron scattering measurements of magnetic excitations in the charge-ordered state of Yb4As3 have been performed under magnetic field up to about 6 T. By applying a magnetic field, the spectrum at the one-dimensional wave vector q = 1 [ pi/d] changes drastically from a broad one corresponding to the spinon excitation continuum of the one-dimensional S = 1 / 2 spin system to a sharp one at a finite energy, indicating the opening of an energy gap in the system. The magnetic field dependence of the gap is well fitted by the power law H2/3. The experimental result gives strong evidence for the existence of a staggered field alternating along Yb3+ chains induced by the Dzyaloshinsky-Moriya interaction.