Dispersive Magnetic Density Fluctuations inNi3Ga

We report the first successful measurements of the magnetic fluctuation, or paramagnon, spectrum of an exchange-enhanced paramagnet. The spectrum measured in pure specimens of ${\mathrm{Ni}}_3$Ga by inelastic neutron scattering can be described by a spin-density relaxation rate $\Gamma \left(\mathrm{q}\right)$ which vanishes at small wave vectors and is strongly dispersive. The experimental findings are analyzed in terms of the theory of a Fermi liquid in the collisionless quasiparticle regime.