Acoplamento spin-fônon em peroviskitas duplas ordenadas multiferróicas investigado por Espectroscopia Raman

• Ano de defesa: 2014
• Autor(a) principal: Macedo Filho, Raimundo Bezerra
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Palavras-chave em Português: Perovskita - transição ferromagnética; Propriedades multiferroicas; Síntese de estado sólido; Acoplamento spin-fônon; Espectroscopia de Raman
• Link de acesso: http://www.repositorio.ufc.br/handle/riufc/12228

In this study, we investigated the influence RE (rare earth) ionic radius on the spon-phonon coupling in the RE2NiMnO6 (RE = Y, Nd and Gd) double perovskites family by Raman spectroscopy. Recently, ab intio calculations based on the Density Functional Theory (DFT) showed that compounds os this family may have multiferroics properties. Furthermore, the La2NiMnO6 perovskite undergoes a ferromagnetic transition near to room temperature, Tc ~ 280 K. In this scenario, RE2NiMnO6 samples were synthesized by the conventional solid state method. The analysis of powder X-ray diffraction petterns confirmed the monoclinic phase for all samples belonging to the space group P2ᶦ/n (C2h⁵). Raman spectroscopy measurements as a function of temperature showed no changes that could suggest a structural phase transition. However, the Raman frequency of the most intense mode of the Raman spectrum, attributed to the symmetric stretching mode of the oxygen octahedra, showed a deviation (anomalies) very close to the ferromagnetic transition of each compound. This anomaly was associate with the spon-phonon coupling, however, the intensity of this coupling showed no significative dependence on the RE ionic radius. Based on these results it was suggested that the RE ionic radius should not be a predominant parameter on the intensity of the spin-phonon coupling, especially in the case of ordered RE2NiMnO6 double perovskites.