Magnetic Properties of Quasi-Two-Dimensional Non-Kramers Magnets TmX3 and TmOX (X=Cl,Br,I)
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Katta, Shreenithi Sai
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Abstract
Rare-earth halides and oxyhalides materials — LnX3 and LnOX — provide a platform for interesting magnetic behavior due to their simple crystal structures and large anisotropic moments. Though many have been studied in detail, there is a large gap in literature concerning the structural and magnetic behavior of TmX3 and TmOX (X=Cl,Br,I). Therefore, this project seeks to fill the gap in knowledge through complete structural and magnetic characterization of TmBr3 and TmI3 and partial characterization of TmOBr using x-ray diffraction, magnetization measurements, low temperature heat capacity, and neutron spectroscopy. Here, we report TmBr3 and TmI3 both crystallize into the trigonal space group R-3 with antiferromagnetic signatures present in magnetization measurements. Neutron diffraction corroborates a magnetic ordering transition in both materials seen in heat capacity around 1 Kelvin. The entropy release across the magnetic transition in TmI3 is anomalously low, indicating crystal field effects may be at play. Inelastic scattering at 5 Kelvin displays a singular neutron-excited crystal field mode in both materials along with a possible low energy magnetic excitation in TmBr3. Magnetic diffraction done below ordering temperature presents two weak magnetic Bragg peaks in TmBr3 and a weaker magnetic Bragg peak in TmI3. Further analysis is needed to identify the exact magnetic structure of both materials and understand the effects of the crystal electric field. Partial characterization of polycrystalline TmOBr indicates antiferromagnetic signatures and a magnetic ordering transition around 1 Kelvin. An anomalous peak appears at 0.2 K in addition to the ordering peak only under an applied field of 1 Tesla. Further measurement and analysis is needed to corroborate these results and identify the magnetic structure of TmOBr. Nonetheless, this work fills the gap in literature on TmX3 and TmOX (X=Cl,Br,I), providing a foundation for further work to build upon.
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Undergraduate Research Option Thesis