Marcela F. Silva, Luiz A. S. de Oliveira, Mariani A. Ciciliati, Lais T. Silva, Bruna S. Pereira, Ana A.W. Hechenleitner, Daniela M. F. Oliveira, Kleber R. Pirota, Flavio F. Ivashita, Andra Paesano Jr., J. Martin Pastor, J. I. Perez-Landazabal e Edgardo A. G. Pineda

JOURNAL OF APPLIED PHYSICS – Volume: 114; Issue: 10; Article Number: 104311; DOI: 10.1063/1.4821253

Fe2O3 nanoparticles with sizes ranging from 15 to 53 nm were synthesized by a modified sol-gel method. Maghemite particles as well as particles with admixture of maghemite and hematite were obtained and characterized by XRD, FTIR, UV-Vis photoacoustic and Mossbauer spectroscopy, TEM, and magnetic measurements. The size and hematite/maghemite ratio of the nanoparticles were controlled by changing the Fe:PVA (poly (vinyl alcohol)) monomeric unit ratio used in the medium reaction (1:6, 1:12, 1:18, and 1:24). The average size of the nanoparticles decreases, and the maghemite content increases with increasing PVA amount until 1:18 ratio. The maghemite and hematite nanoparticles showed cubic and hexagonal morphology, respectively. Direct band gap energy were 1.77 and 1.91 eV for A6 and A18 samples. Zero-field-cooling-field-cooling curves show that samples present superparamagnetic behavior. Maghemite-hematite phase transition and hematite Neel transition were observed near 700K and 1015 K, respectively. Magnetization of the particles increases consistently with the increase in the amount of PVA used in the synthesis. Mossbauer spectra were adjusted with a hematite sextet and maghemite distribution for A6, A12, and A24 and with maghemite distribution for A18, in agreement with XRD results. (C) 2013 AIP Publishing LLC.