Spin correlations in the geometrically frustrated pyrochlore Tb₂Mo₂O₇

We report neutron-scattering studies of the spin correlations of the geometrically frustrated pyrochlore Tb₂Mo₂O₇ using single-crystal samples. This material undergoes a spin-freezing transition below T_g≃24 K, similar to Y₂Mo₂O₇, and has little apparent chemical disorder. Diffuse elastic peaks are observed at low temperatures, indicating short-range ordering of the Tb moments in an arrangement where the Tb moments are slightly rotated from the preferred directions of the spin-ice structure. In addition, a Q⃗-independent signal is observed which likely originates from frozen but completely uncorrelated Tb moments. Inelastic measurements show the absence of sharp peaks due to crystal-field excitations. These data show how the physics of the Tb sublattice responds to the glassy behavior of the Mo sublattice with the associated effects of lattice disorder.