Impact of Stoichiometry of Yb$_{\mathrm{2+}}_{x}$Ti$_{\mathrm{2-}}_{x}$O$_{\mathrm{7-}}_{x}_{\mathrm{/2}}$ on its Structure and Physical Properties

The rare-earth pyrochlores ($R_{\mathrm{2}}M_{\mathrm{2}}$O$_{\mathrm{7}})$ are topic of intense study in the field of magnetism as an ideal host for geometric frustration including spin-liquid and spin-ice behaviour. Specifically, $R_{\mathrm{2}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7\thinspace }}$has proved a rich playground: compounds $R \quad =$ Ho and Dy are classical spin ices, $R \quad =$ Tb has been shown to be a spin liquid at low temperatures, and $R \quad =$ Yb is a candidate quantum spin ice. This system is attractive for the large anisotropic magnetic properties of rare earth ions, Ti$^{\mathrm{4+}}$'s lack of magnetic moment which isolates the magnetic ordering of $R^{\mathrm{3+}}$, and the comparative ease of making single crystals via the floating zone technique. This talk will present the structure and physical properties of a Yb$_{\mathrm{2+}}_{x}$Ti$_{\mathrm{2-}}_{x}$O$_{\mathrm{7-}}_{x}_{\mathrm{/2}}$ series including both the pure and stuffed samples. The series shows a dramatic change in the low-temperature (50-200 mK) specific heat signature upon doping away from the pure compound. Understanding the magnetic and physical properties of the off-stoichiometric series sheds light both on the magnetic ordering of the ideal spin ice candidate compound as well as aids in evaluating the quality and stoichiometry of a measured sample. In this vein, proper single-crystal growth conditions in order to ensure single crystals of appropriate stoichiometry will also be discussed.