  We report neutron scattering experiments performed to investigate the dynamic
magnetic properties of the Kondo-lattice compound YbNi2B2C. The spectrum of
magnetic excitations is found to be broad, extending up to at least 150 meV,
and contains inelastic peaks centred near 18 meV and 43 meV. At low energies we
observe quasielastic scattering with a width Gamma = 2.1 meV. The results
suggest a Yb3+ ground state with predominantly localized 4f electrons subject
to (i) a crystalline electric field (CEF) potential, and (ii) a Kondo
interaction, which at low temperatures is about an order of magnitude smaller
than the CEF interaction. From an analysis of the dynamic magnetic response we
conclude that the crystalline electric field acting on the Yb ions has a
similar anisotropy to that in other RNi2B2C compounds, but is uniformly
enhanced by almost a factor of 2. The static and dynamic magnetic properties of
YbNi2B2C are found to be reconciled quite well by means of an approximation
scheme to the Anderson impurity model, and this procedure also indicates that
the effective Kondo interaction varies with temperature due to the crystal
field splitting. We discuss the nature of the correlated-electron ground state
of YbNi2B2C based on these and other experimental results, and suggest that
this compound might be close to a quantum critical point on the non-magnetic
side.

Strongly Correlated Electrons