Inelastic neutron-scattering experiments have been performed on a single crystal of $\left({\mathrm{Y}}_{0.97}{\mathrm{Sc}}_{0.03}\right){\mathrm{Mn}}_2$. 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 centered 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.

• Received 8 August 1995

DOI:https://doi.org/10.1103/PhysRevLett.76.2125