Cr³⁺substituted spinel ferrite nanoparticles with high coercivity

Abstract

The low coercivity of spinel ferrites is a major barrier that significantly limits their use in high density magnetic recording applications. By controlling the substituting content of Cr(3+), in this article we describe how magnetic CoCr x Fe2-x O4 (0 < x < 1.2) nanoparticles with coercivity of up to 6.4 kOe were successfully obtained by the hydrothermal process. The high coercivity is attributed to the synergetic effects of magnetocrystalline anisotropy and the nanoscale size effect. X-ray diffraction analysis confirmed the spinel structure of the nanoparticles with transmission electron microscopy (TEM) suggesting regular tetragonal morphology. The TEM indicated an edge length ranging from 15 nm to 150 nm, which increases monotonically with increasing Cr content. Raman analyses supported the proposed model on the formation mechanism of the nanoparticles, i.e. heterogeneous and homogeneous nucleation.

Synthesis of CoFe2O4 magnetic nanoparticles for application in photocatalytic removal of azithromycin from wastewater

“…The cobalt ferrite shows a ferromagnetic behavior with the saturation magnetization (M S ) of about 69 emu/g. This result (M S value) is similar to those reported by other studies 31,32 for CoFe 2 O 4 magnetic nanoparticles. Mosleh et al 33 reported the maximum M S value of 46 emu/g for BaFe 12 O 19 magnetic nanoparticles.…”

Novel nanoparticles with Cr3+ substituted ferrite for self-regulating temperature hyperthermia

“…In our previous work, we found that substituting Fe 3+ by nonmagnetic Cr 3+ in the spinel ferrite nanoparticles can decrease the Curie temperature and increase H c simultaneously, which is attributed to the effect of Cr 3+ on the spinel structure of ferrite in the formation process of nanoparticles. [21][22][23] In addition, the analogous valence-bond structure and similar radius of Fe 3+ and Cr 3+ makes their amorphous hydroxide precipitates behave thermodynamically to true solid solutions and consequently the Cr 3+ may be substituted into Co-Zn ferrite without breaking its spinel lattice structure and symmetry. 24 44.0 o C) and its specific absorption rate (SAR) is 774 W kg -1 which is two folds higher than the SAR standard for magnetic nanoparticles used in hyperthermia, 25 under magnetic field with the frequency and intensity at 100 kHz and 200 Oe.…”

Influence of annealing on magnetic induction heating efficiency of Zn–Co–Cr ferrite nanoparticles

“…In addition, since the magnetocrystalline anisotropy of CoFe 2 O 4 mainly arises from the incompletely quenched orbital momentum of Co 2+ at B sites [30], if the Co 2+ migrates from B sites to A sites, the magnetocrystalline anisotropy constant will decrease [31]. The magnetocrystalline anisotropy constant can be estimated by the Wohlfarth's relation [32]. The calculated results by the data of Fig.…”