| Materials with a geometrically frustrated magnetic pyrochlore lattice have been of interest due to their unusual ground states. Tb2Ti 2O7 is known for having a spin liquid ground state which does not transition to a long-range ordered state down to at least 50 mK. Ho2Ti2O7 has a macroscopically degenerate spin ice ground state which resembles that of the proton ordering in water ice. Heat Capacity measurements of Tb2Ti2- xSnxO7 were done down to 0.36 K and AC magnetic susceptibility measurements of Ho2- xYxTi2O7 and Ho2-xLaxTi 2O7 were done for frequencies from 10 Hz to 10 kHz down to 1.8 K, both in magnetic fields up to 9 T. These experiments were performed in an effort to further understanding of the factors that lead to their unusual behavior and to study the effects of introducing disorder through doping with nonmagnetic elements. Determination of the effect of an external field on the hyperfine crystal field at the Tb sites was done. In addition, unusual behavior in the ac susceptibility of the Ho samples at lower temperatures was observed. |
