abstract
The structural and magnetic properties of Ba(1-x)Gd(x)Fe(12)O19 (0 < x < 0.15) nanoparticles prepared using the proteic sol-gel process were investigated. Infrared spectroscopy, Raman spectroscopy, and X-ray powder diffraction measurements with Rietveld refinement analysis confirmed the formation of M-type BaFe12O19, whereas extra peaks of secondary phases were also detected for BaFeO3 (2 theta = 28), GdFeO3 (2 theta = 38.4), and Fe2O3 (2 theta = 38.6). Average crystallite size increases with Gd substitution in the range of 61-63 nm. Scanning electron microscopy revealed that the particle morphology of some samples consisted of a tendency for regular hexagonal platelets with inhomogeneous distribution of average grain size in the range of 250-280 nm. The room temperature magnetic studies revealed that considerable large saturation magnetization (Ms), remanence (Mr), and coercivity (Hc) for the Ba(1-x)GdxFe(12)O(19) nanoparticles monotonically decreased to a minimum value until x = 0.1. However, it increased again to Ms asymptotic to 55.5 emu.g(-1), Mr asymptotic to 22.7 emu.g? 1, and Hc asymptotic to 3.7 kOe for the x = 0.15 sample. The squareness ratio (SQR = Mr/Ms) values were lower than 0.5, illustrating the magnetic multidomain nature and uniaxial anisotropy of the samples. These results were investigated deeply with relation to hyperfine parameters and surface morphology of the samples by 57Fe Mo & BULL;ssbauer spectroscopy and magnetic force microscopy (MFM). The hyperfine parameters indicated that the substitution of Gd3+ for Ba2+ induces exchange interactions in 2b-O2-4f2 and 12k-O2-2b, resulting in the higher magnetocrystalline anisotropy of the samples. Additionally, MFM images confirm that grain consisting of distributed smaller grains gives rise to a strip-and helix-like magnetic domain structure.
keywords
SOL-GEL AUTOCOMBUSTION; HEXAGONAL FERRITES; ELECTRICAL-PROPERTIES; MICROWAVE-ABSORPTION; SUBSTITUTION; MICROSTRUCTURE; GROWTH; IONS
subject category
Materials Science; Physics
authors
Buzinaro, MAP; Costa, BFO; Ivanov, MS; Cunha, GC; Macedo, MA; Angelica, RS; Ferreira, NS
our authors
Maxim Ivanov
Junior Researcheracknowledgements
The authors acknowledge financial support from the funding agencies Fundacao de Apoio a Pesquisa e a Inovacao Tecnologica do Estado de Sergipe-FAPITEC/SE [TER_OUTORGA:14023.422], Conselho Nacional de Desenvolvimento Cientifico e Tecnologico-CNPq [grant no. 309054/2019-2 and 309176/2019-0]. The Coimbra Physics Centre supported by FCT (UIDB/04564/2020 and UIDP/04564/2020), TAILUC facility funded under QREN-Mais Centro project (ICT_2009_02_012_1890), Netzsch do Brasil Ind. Com. Ltda, and Petrobras/ANP sponsorship is also acknowledged. Additionally, M. Ivanov is grateful to the RSF (Grant 20-79-10223).