Yb–Yb correlations and crystal-field effects in the Kondo insulatorYbB12 and its solid solutions

Abstract

We have studied the effect of Lu substitution on the spin dynamics of the Kondo insulatorYbB12 to clarify the origin of the spin-gap response previously observed at lowtemperature in this material. Inelastic neutron spectra have been measured inYb1−xLuxB12 compounds for fourLu concentrations, x = 0, 0.25, 0.90 and 1.0. The data indicate that the disruption of coherence on the Ybsublattice primarily affects the narrow peak structure occurring near 15–20 meV in pureYbB12, whereas the spin gap and the broad magnetic signal around 38 meV remain almostunaffected. It is inferred that the latter features reflect mainly local, single-site processes,and may be reminiscent of the inelastic magnetic response reported for mixed-valenceintermetallic compounds. On the other hand, the lower component at 15 meV is most likelydue to dynamic short-range magnetic correlations. The crystal-field splitting inYbB12 estimated fromthe Er3+ transitionsmeasured in a Yb0.9Er0.1B12 sample has the same order of magnitude as other relevant energy scales of the system,and is thus likely to play a role in the form of the magnetic spectral response.