Magnetic relaxation in UCu_{4 + x}Al_{8 - x}

Abstract

A quasielastic neutron scattering study has been performed on UCu_4+xAl_8-x, a system which reveals an alloying-induced transition from magnetic order to heavy-fermion behavior. The magnetic response can be described by a broad quasielastic Lorentzian for all concentrations. No crystal field excitations could be detected. Remarkably, the linewidth decreases with increasing hybridization strength and seems to be no measure of the Kondo lattice temperature T*. In addition, electron spin resonance (ESR) experiments were performed which revealed that, even in the heavy-fermion regime, spin fluctuations play an important role. Both experimental findings are in distinct contrast to cerium-based heavy fermion systems.