Magnetic excitation spectrum of Kondo-insulator YbB12

The dynamic magnetic response of intermediate valence (YbB12)-B-11 has been studied by inelastic neutron scattering on the HET time-of-flight spectrometer, with incident energies E-i = 200 meV at T = 15K and E-i = 80 meV at T = 15-160 K. The low-temperature magnetic response spectrum has a fine structure with a cut off at about 40 meV. No quasielastic magnetic scattering was detected at T = 15 K. Increasing temperature results in a transformation of the YbB12 magnetic response into one dominated by a quasielastic peak. The characteristic features of the temperature dependence of the bulk magnetic susceptibility are analyzed on the basis of the observed evolution of the spectrum. (C) 2000 Elsevier Science B.V. All rights reserved.