Spin-glass-like magnetic ground state of the geometrically frustrated pyrochlore niobate Tb2Nb2O7 -: art. no. 174413

dc (chi) and ac (chi(ac)) magnetic susceptibilities, field dependence of isothermal magnetization and specific heat C-P measurements have been performed on a pyrochlore geometrically frustrated niobate Tb2Nb2O7. The chi characteristics is consistent with collective paramagnetism down to at least Tapproximate to2 K with effective nearest-neighbor antiferromagnetic interactions, J(eff)=-1.5 K, among magnetic ions. Crystal-field calculation shows that Tb3+ ground state is an isolated Ising-like S=1/2 doublet with anisotropic g tensor and Tb3+ spins pointing along local <111> directions of tetrahedral unit of pyrochlore structure. The ground-state doublet is further modified by the short-range spin-spin correlations, giving rise to a rounded peak at 1.9 K in zero-field magnetic specific heat C-mag. In addition, the frequency-dependent peak in chi(ac) at about 0.8 K indicates spin-glass-like freezing of Tb3+ spins in Tb2Nb2O7. Tb2Nb2O7 is compared with other geometrically frustrated Tb-based pyrochlores, e.g., a spin-glass Tb2Mo2O7 and a collective paramagnet-spin liquid Tb2Ti2O7.