Mechano-Synthesis, Characterization, and Magnetic Properties of Nanoparticles of Cobalt Ferrite, CoFe₂O₄

Abstract

Cobalt ferrite, CoFe 2 O 4 , nanoparticles have been obtained from pre-prepared layered double hydroxide carbonate, LDH-CO 3 , by mechanical milling. X-ray powder diffraction shows the only product of the milling for 5 h of the LDH-CO 3 is cobalt ferrite nanoparticles. Longerterm milling induces particle growth characterized by sharpening of the Bragg peaks and an increase of the blocking temperature, while prolonged milling results in the formation of some cobalt metal. Mo ¨ssbauer spectra and temperature dependence of the magnetization of the 5-h milled sample suggest that it consists of nanoparticles of size less than 10 nm with blocking temperature of 200 K, in good agreement with microscopy showing an average size of 6 nm. The magnetic properties exhibit a strong dependence on the particle size as a result of an unusual cation distribution and of surface effect. The saturation magnetization at 5 K and the squareness of the hysteresis loops increase with the average particle size. The difference between zero-field-cooled and field-cooled hysteresis loops is correlated with the presence of randomness of the moments at the surface.

Determination of the cation site distribution of the spinel in multiferroic CoFe 2 O 4 /BaTiO 3 layers by X-ray photoelectron spectroscopy

“…We already know that bulk CoFe 2 O 4 has several key properties such as strong magneto-crystalline anisotropy, high magnetostriction and saturation magnetization, as well as high coercive fields at room temperature [3,4]. Bulk CoFe 2 O 4 crystallizes in the spinel structure with a lattice parameter of 0.838 nm.…”

Characterization of nanodimensional Ni-Zn ferrite prepared by mechanochemical and thermal methods

“…Figure 1 shows the RT Mössbauer spectra of samples obtained after different processing routes. The corresponding parameters, listed in Table 2, are typical of Fe 3+ ions in octahedral and tetrahedral spinel sites [1,6,7]. As shown in Figure 1A the spectra of all milled samples are doublets.…”

“…The mechanochemical synthesis (MS) of nickel-zinc ferrite powders was performed by two steps: (i) co-precipitation, and (ii) high-energy ball-milling (3h to obtain Ni 1-x Zn x Fe 2 O 4 (x = 0.2, 0.5, 0.8, 1.0) and 6h for NiFe 2 O 4 ) following the procedure, described in [7]. The thermal synthesis (TS) was performed by annealing of the co-precipitation precursors at 773 K. The phase composition and structure was determined by X-ray diffraction (XRD) using TUR M62 diffractometer with Co Kα radiation.…”

“…The properties of these ferrites are highly sensitive to the cation distribution which in turn depends on the method of preparation and sintering conditions. Spinel-type ferrites can be prepared by a variety of methods [4][5][6][7]. The high-energy milling as a solid-state method for synthesis of nanodimensional materials has the advantage that it can be easily operated and produce large amounts of nanostructured powders in a fairly short time.…”

Mössbauer and magnetic study of Co x Fe3--x O4 nanoparticles

“…However, saturation magnetization (Ms) can be estimated from zero extrapolation of M versus 1/H and the ratio Mr/Ms can be calculated [5]. Both calculated parameters increase with milling time but never reach the theoretical values [6]. This indicates that even for such long treatment time some of the ultrafine particles remain or that the objects formed are core/shell particles with a spin-glass like surface layer [5].…”