Cava, RobertO'Rourke, Leah2018-08-022026-09-292018-08-022026-09-292018-04-152018-08-02http://arks.princeton.edu/ark:/88435/dsp01qn59q672chttps://theses-dissertations.princeton.edu/handle/88435/dsp01qn59q672cGeometric magnetic frustration presents experimental and theoretical challenges for the study of magnetism, and rare earth compounds are rich subjects for such research. I report the synthesis of pure (RE)\(_{2}\)O\(_{2}\)S and nearly pure (RE)\(_{2}\)O\(_{2}\)Se compounds for RE = La, Ho-Yb using standard solid state methods, as well as these compounds’ magnetic properties. All RE = Ho-Yb compounds were found to be antiferromagnetic. Er\(_{2}\)O\(_{2}\)X and Tm\(_{2}\)O\(_{2}\)X exhibit no ordering down to 1.8 K and remain candidates for magnetic frustration. Ho\(_{2}\)O\(_{2}\)S, Ho\(_{2}\)O\(_{2}\)Se, Yb\(_{2}\)O\(_{2}\)S, and Yb\(_{2}\)O\(_{2}\)S order at T\(_{N}\) = 2.4 K, 4.4 K, 2.7 K, and 1.9 K, respectively; none of these systems are frustrated at low temperature. Both series are promising starting points for further magnetic studies, particularly in the search for geometrically frustrated oxychalcogenide pyrochlores.application/pdfenPrinceton University Senior Theses