Cooperative paramagnetism in the geometrically frustrated pyrochlore antiferromagnet Tb₂Ti₂O₇

Neutron scattering, muon spin relaxation, and dc susceptibility studies have been carried out on polycrystalline Tb₂Ti₂O₇a pyrochlore antiferromagnet in which the Tb³⁺ moments reside on a network of corner-sharing tetrahedra. Unlike other geometrically frustrated systems, Tb₂Ti₂O₇ remains paramagnetic down to ∼0.07K, rather than ordering into a conventional Néel or spin-glass-like state, despite the fact that short-range antiferromagnetic correlations (AFC) develop at ∼50K. At the first AFC wave vector, its low-lying, relatively flat magnetic excitation spectrum softens partially below 30 K.