High-resolution neutron scattering study of Tb₂ Mo₂ O₇: A geometrically frustrated spin glass

The low-temperature magnetic properties of Tb₂ Mo₂ O₇ have been studied with bulk susceptibility measurements and with elastic and high-resolution inelastic neutron scattering. This system is a spin glass with a freezing temperature Tg ∼25 K. A reverse Monte Carlo simulation of the neutron diffraction data shows weak ferromagnetic near-neighbor spatial correlations that do not extend beyond 10 Å. Neutron measurements of the spin dynamics reveal a slowing down with decreasing temperature without an anomaly at the glass transition. A low-lying Q -independent mode is seen at ω0 ∼0.28 meV. This dispersionless crystal electric field transition is measurable up to 60 K.