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 spectrom eter, 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 stru cture with a cut off at about 40 meV. No quasielastic magnetic scattering w as 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 magne tic susceptibility are analyzed on the basis of the observed evolution of t he spectrum. (C) 2000 Elsevier Science B.V. All rights reserved.