Síntese e caracterização de perovskitas complexas multiferróicas com estrutura dupla ordenada

Abstract

The RE2CoMnO6 (RE = La e Y) and Gd(Co0.5Mn0.5)O3 samples were obtained via modified Pechini method (MPM). Raman spectroscopy (RS), Fourier transform infrared (FTIR) spectroscopy, X ray powder diffraction, X ray photoelectron spectroscopy (XPS), SQUID and scanning electron microscopy (SEM) were used to characterize the samples, investigate structural and microstructural evolution, as well as evaluate their vibrational, magnetic and intrinsic dielectric properties. The impact of synthesis conditions on the structural ordering was investigated. We obtained a good control of structural order depending on the annealing temperature for LCMO. We observed an increase in the saturation magnetization, lifetime of the phonons and dielectric constant while suppression of anti-site defects and reduction of dielectric loss. Our investigations on polar phonons by FTIR revealed the extrinsic character of CDC effect on LCMO and clarified the contributions of phonons for dielectric constant in these systems. The temperature dependence Raman spectra of GCMO was investigated between 40 and 300 K and revealed an intriguing spin-phonon coupling, characterized by an increase in the energy of the most intense stretching mode near the magnetic transítion. The correlation between the Raman data and the magnetization suggests that the structure influences the magnitude of the spin-phonon coupling. Correlated analysis of LCMO, GCMO and YCMO systems show that all samples have vibrational properties quite similar. The intrinsic dielectric constants were obtained from the polar phonons dispersive parameters ε intr ̴ 15.8, 17.9 and 16.0, making the contributions to this value explicit, as well as the quality factors, reciprocal of dielectric losses , 𝑄𝑢×𝑓 ≈ 124,74 e 83 THz, extrapolated to microwave region at 10 GHz, to LCMO, GCMO and YCMO, respectively. XPS measures showed that oxidation state for Co and Mn ions are similar each another, being mostly Co2 + and Mn4 + for all investigated systems, however to GCMO, the spin-phonon coupling behavior and losses relatively large indicate that this compound has a high level of structural disordering.