Full text
| |
| Author(s): |
Mário Moda Piva
Total Authors: 1
|
| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin |
| Defense date: | 2019-12-06 |
| Examining board members: |
Pascoal José Giglio Pagliuso;
Eduardo Miranda;
Narcizo Marques de Souza Neto;
Raimundo Lora Serrano;
Marcos de Abreu Ávila
|
| Advisor: | Pascoal José Giglio Pagliuso |
| Abstract | |
Many compounds with novel ground states, such as unconventional superconductivity, complex magnetic structures and non-Fermi-liquid states crystallize in layered structures. Moreover, these ground states can be tuned by chemical substitution, magnetic fields and applied hydrostatic pressure. In particular, applied pressure is an ideal tuning parameter, as there is no chemical disorder introduced in the system. Therefore, the application of external pressure is a desirable route to induce unusual ground states. In this thesis, we report the pressure dependence of the properties of the antiferromagnetic layered materials: CeYBi2 (Y = Cu and Au), CeAu2Bi, CaMn2Bi2 and Sr(Fe1-xCox)2As2. Single crystals of these compounds were synthesized by the metallic-flux technique. The synthesized phase was characterized by x-ray diffraction, EDX, magnetic susceptibility, specific heat and electrical resistivity measurements at ambient pressure. Electrical resistivity and AC calorimetry experiments under pressure were performed to study the evolution of the properties as a function of pressure. The antiferromagnetic order in CeCuBi2 was suppressed with the application of external pressure and a zero resistance state (ZRS) was found at high pressures. For CeAuBi2 the application of external pressure favored the antiferromagnetism (AF) and a ZRS was again found with similar transition temperatures to CeCuBi2 and at similar pressures. Moreover, CeAu2Bi and CaMn2Bi2 have also shown an enhancement of the Nèel temperature (TN) as a function of increasing pressure. In addition, applied pressure enhanced the activation energy of CaMn2Bi2. Finally, Sr(Fe1-xCox)2As2 presented a suppression of the spin-density-wave (SDW) phase along with the appearance of a superconducting state with increasing pressure and/or Co concentration. In all cases, the pressure dependent experiments were successfully applied to extract relevant parameters and provided new insights to the underlying physical phenomena of the studied systems. These insights will be discussed, specifically, for each family of compounds throughout the thesis and summarized in chapter 5, Conclusions and Perspectives (AU) | |
| FAPESP's process: | 15/15665-3 - Studies of orbital differentiation effects in the magnetic and superconducting properties of FeAs based compounds |
| Grantee: | Mário Moda Piva |
| Support Opportunities: | Scholarships in Brazil - Doctorate (Direct) |