Inelastic neutron scattering experiments performed for the first time on a single crystal of (Y_0.97Sc_0.03)Mn₂. The spin fluctuation spectrum is broad in energy and strongly correlated in wave vector, with maximum intensity at the Brillouin zone boundary. There is no magnetic scattering for Brillouin zones centred at the origin and at certain reciprocal lattice points, suggesting the existence of short-lived 4-site collective spin singlets. The unusual features of the dynamical susceptibility discovered in this experiment result from geometrical frustration and give new insight into the heavy-fermion like behavior of the compound.

Phys. Rev. Letters 76 12 (1996) pp. 2125-2128

Submitted by Dr. Eddy LELIEVRE-BERNA of the Institut Laue-Langevin.