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| Author(s): |
Gabriel Silva Freitas
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin |
| Defense date: | 2024-04-19 |
| Examining board members: |
Pascoal José Giglio Pagliuso;
Mucio Amado Continentino;
Francisco Paulo Marques Rouxinol;
Raimundo Lora Serrano;
Diego Muraca
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| Advisor: | Pascoal José Giglio Pagliuso |
| Abstract | |
In this work, we delve into the studies of the physical properties of AMZ2 (A = Rare earth/Actinide; M = Transition metal; Z = pnicogens) compounds, which we generalize as 112 crystalline structure. Our focus is on elucidating the impact of crystalline electric field (CEF) effects in rare-earth-based intermetallic compounds within this structure. In particular, we have investigated the RTBi2 (R = Rare earth; T = Cu and Au) and the RCuBi2?xSbx series of compounds, as well as the UAgBi2 and YNiSn2 materials. We have employed a comprehensive array of experimental techniques, including X-ray powder diffraction, magnetization, resistivity, specific heat, electron spin resonance, and thermal expansion measurements. Additionally, we applied a theoretical model with a mean-field approximation of the magnetic interactions between the nearest R-neighbors and the tetragonal CEF Hamiltonian to t some of the observed magnetic properties of the studied compounds. In the RTBi2 series, we observed an increase in Neel temperature (TN) upon substituting Cu with a larger ion (Au). This enhancement is attributed to changes in the CEF scheme of levels and magnetic anisotropy, favoring the magnetic moment alignment along the c axis. For the RCuBi2-xSbx series, we uncover a change in magnetic easy axis orientation from the c axis to the basal plane with increasing Sb concentration, accompanied by an evolution of TN. In summary, we aimed to highlight the influence of the CEF effects induced by the chemical substitution on the magnetic properties of the 112 compounds. Additionally, we present the physical properties of the newly synthesized UAgBi2 compound, revealing a complex magnetic structure with multiple magnetic field-induced transitions. Specific heat measurements have revealed four magnetic transitions at temperatures of 67 K, 64 K, 36 K, and 23 K. A HxT phase diagram constructed from specific heat, thermal expansion, and magnetostriction data is proposed to help elucidate the compound's low-T complex magnetic behavior. Lastly, we have synthesized single crystals of YNiSn2, which exhibit intriguing characteristics, including a low density of states at the Fermi level and a remarkable positive magnetoresistance of 800% at low temperatures. Field-induced metal-insulator-like transition and significant dHvA quantum oscillations further add to the compound's unique properties. The possible presence of charge carriers with quasi-linear energy dispersion akin to a Dirac-like semimetal is being investigated (AU) | |
| FAPESP's process: | 19/26247-9 - Emergent phenomena in Bi-based systems with low dimensionality |
| Grantee: | Gabriel Silva Freitas |
| Support Opportunities: | Scholarships in Brazil - Doctorate |