Coexisting Magnetic Order and Cooperative Paramagnetism in the Stuffed Pyrochlore Tb_(2+x)Ti_(2-2x)Nb_xO₇

Neutron scattering and magnetization measurements have been performed on the stuffed pyrochlore system Tb2+xTi2-2xNbxO7. We find that despite the introduction of chemical disorder and increasingly antiferromagnetic interactions, a spin glass transition does not occur for T >= 1.5 K and cooperative paramagnetic behavior exists for all x. For x = 1, Tb3NbO7, 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.