Coexisting magnetic order and cooperative paramagnetism in the stuffed pyrochlore Tb2+x Ti2-2x Nbx O7

Neutron-scattering and magnetization measurements have been performed on the stuffed pyrochlore system Tb2+x Ti2-2x Nbx O7. We find that despite the introduction of chemical disorder and increasingly antiferromagnetic interactions, a spin-glass transition does not occur for T≥1.5K and cooperative paramagnetic behavior exists for all x. For x=1, Tb3 NbO7, an antiferromagnetically ordered state coexisting with cooperative paramagnetic behavior is seen without applying any external fields or pressure, a situation advantageous for studying this cooperative behavior.