Yb-Yb correlations and crystal-field effects in the Kondo insulator YbB12 and its solid solutions

TL;DR

This study investigates how lutetium substitution affects the spin dynamics and magnetic responses in the Kondo insulator YbB12, revealing the local versus coherence-related origins of its spectral features.

Contribution

It provides new insights into the local and collective magnetic processes in YbB12 through neutron scattering and crystal-field analysis, clarifying the origins of its spin-gap features.

Findings

Disruption of Yb sublattice coherence affects the 15-20 meV peak.

The 38 meV magnetic signal remains unaffected by Lu substitution.

Crystal-field splitting is comparable to other energy scales in the system.

Abstract

We have studied the effect of Lu substitution on the spin dynamics of the Kondo insulator YbB12 to clarify the origin of the spin-gap response previously observed at low temperature in this material. Inelastic neutron spectra have been measured in Yb1-xLuxB12 compounds for four Lu concentrations x = 0, 0.25, 0.90 and 1.0. The data indicate that the disruption of coherence on the Yb sublattice primarily affects the narrow peak structure occurring near 15-20 meV in pure YbB12, whereas the spin gap and the broad magnetic signal around 38 meV remain almost unaffected. 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-valence intermetallic compounds. On the other hand, the lower component at 15 meV is most likely due to dynamic short-range magnetic correlations. The crystal-field splitting in YbB12 estimated from the Er3+ transitions measured 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.