Morosan, Emilia2022-09-232022-09-232022-082022-08-12August 202Qian, Long. "Unconventional magnetic order in rare earth intermetallics RT3Si7 (R = Gd-Lu, T = Co, Rh, Ir)." (2022) Diss., Rice University. <a href="https://hdl.handle.net/1911/113272">https://hdl.handle.net/1911/113272</a>.https://hdl.handle.net/1911/113272The distinct properties of rare earth compounds often originate from several interactions and disentangling the mechanisms behind them is of particular interests to solid state chemists and physicists. This dissertation focuses on the rare earth intermetallic compound family RT3Si7 (R = Gd-Lu, T = Co, Rh, Ir), to explore the intricate physics and interactions behind their magnetic and transport properties. The RRh3Si7 (R = Gd-Yb) compounds show diverse physical properties due to the complex competition between different interactions, which causes a breakdown of de Gennes scaling in magnetic ordering temperature along the series. When it comes to each compound, GdRh3Si7 is dominated by the Ruderman-Kittel-Kasuda-Yosida (RKKY) interaction and shows isotropic magnetic behavior. RRh3Si7 (R = Tb-Tm) have lower-than-expected saturated magnetic moments as the crystal field splits their ground state multiplets. Kondo effect results in the hard axis ordering in YbRh3Si7. The second part of the dissertation focuses on Co doped YbRh3Si7 and how Co changes the magnetism of the YbRh3Si7. With Co doping, the magnetic ordering temperature increases from 7.5 K to a remarkable 15.6 K which is the second highest among Yb-based heavy fermion (HF) compounds. It also contradicts the general trend where the magnetic ordering temperature is expected to increase with decreasing Yb-Yb distance (dYb-Yb) as Co doped YbRh3Si7 has some of the highest dYb-Yb. Another effect of Co doping is the crossover from antiferromagnetism to ferromagnetism, due to its tipping of the delicate energy balance between the states with the moment parallel to a and c axis. In the final part of the dissertation, the same systematic study used in RRh3Si7 (R = Gd-Yb) is performed on RIr3Si7 (R = Tb, Tm). With only RKKY and crystal electric field (CEF) interactions in the system, the two compounds show varied physical properties: The structural analysis revealed an abnormal departure from lanthanide contraction in the series. What’s more, the magnetic ground state switches from antiferromagnetic in TbRh3Si7 to canted ferromagnetic in TmRh3Si7. The transport measurements point to low carrier density semimetal behaviors in both compounds, as well as complete opposite field dependence in their magnetoresistance.application/pdfengCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.Heavy fermionCondensed matterSolid state chemistryRuderman-Kittel-Kasuya-Yosida interactionCrystal electric field interactionKondo interactionThesis2022-09-23