부산대학교 도서관

Highlights • CoFe 2 O 4 mixed spinel nanoparticles synthesized by a low-temperature route. • Dispersion in sol-gel SiO 2 for protected annealing without aggregation and coarsening. • Increased crystallinity from structural and morphological changes. • Discussion of the evolution of the magnetic properties upon heating. • Identification of the main source of disorder: Co/Fe distribution in the cation sites. Abstract Cobalt ferrite nanoparticles (d ∼ 11 nm, σ d = 0.5) produced by coprecipitation at room temperature are heat treated up to 1000 °C after a preliminary dispersion in a sol-gel silica matrix to avoid aggregation and coarsening. This protected annealing allows for a significant increase of the crystallinity of the particles, as demonstrated by combined x-ray diffraction and transmission electron microscopy experiments. A large increase in the coercive field value is reported, from 1.0 to 1.6 Tesla after annealing at 600 °C. This enhanced coercivity can be explained by the cumulative effect of an increased magnetic anisotropy and of a decreased saturation magnetization (M s). Mössbauer spectroscopy experiments show that these evolutions of the M s and anisotropy constant (K) values originate from a small increase in canting angles and in inversion degree, i.e. a displacement of Co2+ ions from tetrahedral to octahedral sites of the spinel lattice. This study emphasizes the little impact of an improved crystallinity on saturation magnetization and canting angle values in coprecipitated CoFe 2 O 4 nanoparticles and highlights that the main source of magnetic disorder is associated with the distribution of Co and Fe within the cationic sites. [ABSTRACT FROM AUTHOR]