Thesis advisor: Michael Graf / The R5T4 compounds (R = rare earth, T = Ge or Si) are interesting because the magnetic properties are very sensitively dependent on slight changes in the crystalline structure. Yb5Ge4 is one such compound, with (presumed) antiferromagnetic order occurring at TN = 1.7 K. We are interested in the effects of substituting Li in place of one Yb atom. Previous measurements of the magnetic properties of polycrystalline Yb4LiGe4 using NMR, specific heat, and resistance measurements at temperatures down to 0.5 K and in magnetic fields up to 4 Tesla were made to compare results with the parent compound. The resistance measurements showed a maximum at 1.1 K, which may indicate the onset of magnetic order. Thus we performed μSR measurements on Yb4LiGe4 and Yb5Ge4, and analysis of the data confirmed magnetic ordering (possibly antiferromagnetic) at 1.1 K. The μSR measurements also revealed a dependence on the magnetic history of the sample. Currently we are studying the pressure dependence of the (presumed) Néel Temperature in order to explore whether increased pressure can drive the TN to 0 K, and results will be discussed. / Thesis (BS) — Boston College, 2010. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Physics Honors Program. / Discipline: Physics.