Cooperative Paramagnetic Behavior in the Stuffed Pyrochlore Tb$_{2+ \textit{x}}$Ti$_{2-2 \textit{x}}$Nb$_{ \textit{x}}$O$_{7}$

The pyrochlore Tb$_{2}$Ti$_{2}$O$_{7}$ is a cooperative paramagnet that has generated much interest in the frustrated magnetism community due to the presence of persistent short range spin-spin correlations and its apparent lack of long range magnetic order down to temperatures below $\textit{T}$ = 0.05 K, despite an effective spin-spin interaction strength given by \textit{$\theta_{W}$} $\sim$ 10 K. Motivated by recent work on the stuffed spin ices, we have begun investigations into stuffed variants of Tb$_{2}$Ti$_{2}$O$_{7}$, in which we replace some of the nonmagnetic Ti$^{4+}$ with magnetic Tb$^{3+}$, thus gradually changing the geometry of the magnetic sublattice from a lattice of corner sharing tetrahedra to a disordered lattice of side sharing tetrahedra. Here, we present results from magnetization and neutron scattering studies on powder samples of Tb$_{2+ \textit{x}}$Ti$_{2-2 \textit{x}}$Nb$_{ \textit{x}}$O$_{7}$, where $\textit{x}$ = 0.2, 0.4, 0.6, or 1, where diffraction data indicate that the $\textit{x}$ = 1 material has a disordered fluorite lattice. Preliminary results indicate that short range magnetic correlations similar to those present in Tb$_{2}$Ti$_{2}$O$_{7}$ exist in all of the materials studied, and that long range antiferromagnetic order may exist in the $\textit{x}$ = 1 material.