Coercivity of γ-Fe2O3 particles growing iron-cobalt ferrite

Abstract

Acicular γ-Fe2O3 particles were heated at 90°C in alkali solution containing Co2+ and Fe2+. The coercivity of the resultant particles remarkably increased with the increasing Co2+/Fe2+ ratio, and in the neighborhood of the Co2+/Fe2+ ratio of 0.4, reached a maximum value. When the particles with a Co2+/Fe2+ ratio of 0.5 were dissolved in hydrochloric acid, the cobalt content and the coercivity were rapidly decreased with increasing dissolved weight. Iron-cobalt ferrite was expected to grow on the surface of γ-Fe2O3 particles. The increase of coercivity was attributed to the iron-cobalt ferrite.

Novel Synthesis of Silica‐Coated Ferrite Nanoparticles Prepared Using Water‐in‐Oil Microemulsion

“…On the other hand, the coercivity was rapidly increased with increases in the Co/Fe ratio, and reached a maximum value near a Co/Fe ratio of 0.3-0.4. This result was very similar to that described in Kishimoto's report 31 in which a maximum value of the coercivity for the iron-cobalt ferrite represented by Co x Fe 3Ϫx O 4 was obtained at x Ϸ 0.75 (Co/Fe ϭ 0.33). As the Co/Fe ratio was increased from 0.4 to 0.5, the coercivity was slightly decreased from 780 to 740 Oe, and at the Co:Fe ratio of 0.6, the obtained coercivity of 460 Oe was much smaller than that at the Co:Fe ratio of 0.3 and 0.4.…”

Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles

“…Namely, M S decreases and H C rises as the amount of hard phase is increased [106,107,249,260,293]. However, in certain cases, if the difference in M S between the counterparts is small (e.g., hard Co-ferrite and soft Mnferrite both with M S ~ 80 Am 2 /kg (80 emu/g) at room temperature), although M S remains rather constant with the relative amount of hard and soft phase, H C does evolve according to the hard/soft volume ratio [101,102,143,[251][252][253]262,292]. There exist some systematic studies fixing the core size and methodically increasing the shell size both for conventional hard/soft and inverse soft/hard systems [93,99,101,102,114,125,[127][128][129]132,190,243,248,249,253,263].…”

Magnetic properties of amorphous β-FeOOH nanowire arrays

“…Iron oxyhydroxides (FeOOH), such as a-, b-and g-type, have distinctive properties and are widely used in electrode materials, lithium batteries and preparation of magnetic recording media materials [7][8][9]. b-FeOOH is an antiferromagnetic material with Neel transition temperature T N E270-296 K. As an intermedial precursor, it has been usually used to prepare magnetic recording materials, for example, Fe 3 O 4 and g-Fe 2 O 3 [10].…”