Síntese assistida por sonoquimica e caracterização da hexaferrita SrFe12-2xCoxAlx019

Abstract

In this work, a study of the structural, magnetic, and electrical properties of strontium hexaferrite type-M with the chemical formula SrF e12−x(CoAl)xO19, where 0,0 ⩽ x ⩽ 1,0, prepared by solid-state reaction synthesis assisted by sonochemistry, is presented. The influence of the dopant ions Co2+ and Al3+ on these properties was evaluated. The synthesis parameters were determined based on the study of the effect of sonication time and thermal treatment temperature on a sample of SrF e12O19, which indicated that effective synthesis conditions were 45 minutes of sonication and thermal treatment at 1000◦C for 4 hours. A comparison was made with samples prepared without sonication but with thermal treatment at 1000◦C for 8 hours. Qualitative and quantitative analysis of the phases present, performed using X-ray diffraction and Rietveld refinement methods, revealed the majority presence of the strontium hexaferrite phase (SrM) and a minor hematite phase in all sonochemically assisted samples. The lattice parameters (a and c) and the unit cell volume decrease with the increasing composition of the dopants Co2+ and Al3+. In contrast, non-sonicated samples exhibited non-monotonic behavior of the lattice parameters and three or more phases present. The magnetic properties, evaluated by vibrating sample magnetometry (VSM), showed non-monotonic behavior of the saturation magnetization. However, the remanent magnetization and coercive field presented a minimum value at dopant composition x = 0,4, and the anisotropy constant and anisotropy field showed a minimum at composition x = 0,2. For compositions x ≥ 0,6, these last two properties remained approximately constant. Differences in the magnetic properties’ behavior were observed compared to the system without sonication. The strontium hexaferrite showed a maximum in the magnetic properties at 45 minutes of sonication with thermal treatment at 1000◦C. An interfacial polarization process of MaxwellWagner or space charge was identified through the study of electrical properties: impedance, electric modulus, and permittivities. A conductive process associated with electron hopping at high frequencies was identified via AC conductivity at room temperature. The strontium hexaferrite exhibited two relaxation processes in impedance, which overlap in the electric modulus and are better defined in permittivity and AC conductivity.