Synthesis, characterization and analysis of hyperfine interactions of multiferroic rare earth manganites

Nicole Pereira de Lima. Synthesis, characterization and analysis of hyperfine interactions of multiferroic rare earth manganites. Thesis (Doctorate). Instituto dePesquisas Energéticas e Nucleares (IPEN), University of São Paulo, São Paulo, 2025. This thesis presents an experimental study of local structural distortions and hyperfine interactions in rare-earth manganites and dimanganese pentoxides, with particular attention to the effects of chemical doping. The materials investigated include HoMnO3 and TbMnO3 doped with Cd or La, as well as undoped HoMn2O5 and TbMn2O5. The samples were synthesized using the sol-gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and magnetic measurements. Hyperfine interactions were studied via Perturbed Angular Correlation (PAC) spectroscopy using 111mCd as a nuclear probe, across a wide temperature range. The measurements revealed distinct electric field gradient distributions that reflect structural and electronic changes induced by doping. In particular, the results suggest that dopant incorporation tends to favor the stabilization of the orthorhombic phase, significantly altering the local environment of the probe nuclei. Additionally, the work includes a description of the experimental activities carried out at the ISOLDE facility at CERN, where all the PAC measurements were performed, and of the comissioning of the ASCII chamber, an implantation chamber worked during the research internship. Altogether, this study contributes to the understanding of complex oxide materials and demonstrates the sensitivity of PAC spectroscopy in detecting subtle local distortions and phase transitions driven by doping process.