CoFe₂O₄ and CoFe₂O₄‐SiO₂ Nanoparticle Thin Films with Perpendicular Magnetic Anisotropy for Magnetic and Magneto‐Optical Applications

Abstract

This paper presents an efficient colloidal approach to process CoFe2O4 and SiO2 nanoparticles into thin films for magnetic and magneto‐optical applications. Thin films of varying CoFe2O4‐to‐SiO2 ratios (from 0 to 90 wt%) are obtained by sequential spin coating‐calcination cycles from the corresponding nanoparticle dispersions. Scanning electron microscopy analysis reveals a crack free and nanoparticulate structure of the sintered films with thicknesses of 480–1200 nm. Results from the optical characterization indicate a direct band gap ranging from 2.6 to 3.9 eV depending on the SiO2 content. Similarly, the refractive indices and absorption coefficients are tunable upon SiO2 incorporation. In‐plane measurements of the magnetic properties of the CoFe2O4 films reveal a superparamagnetic behavior with both Co2+ and Fe3+ contributing to the magnetism. Polar Kerr measurements show the presence of a spontaneous magnetization in the CoFe2O4 and CoFe2O4‐SiO2 (with SiO2 < 50 wt%) films, pointing to magnetic anisotropy perpendicular to the substrate. The origin of this effect is attributed to the constrained sintering conditions of the nano­particulate film and the negative magnetostriction of CoFe2O4.

Neoteric Conjugative Electrospinning towards Alloplastic Nanofiber Yarns Affording Enhanced Upconversion Luminescence and Tailored Magnetism

“…CoFe 2 O 4 magnetic nanocrystals have high magnetocrystalline anisotropy and saturation magnetization. As a potential magnetoresistance material and electrical resistance material, CoFe 2 O 4 nanoparticles (NPs) are applied in high‐density magnetic recording medium, high‐performance electromagnetic and spintronic devices . Electrospinning is a method for the preparation of one‐dimensional nanofibers with large aspect ratio and uniform diameter .…”

“…As a potential magnetoresistance material and electrical resistance material, CoFe 2 O 4 nanoparticles (NPs) are applied in high-density magnetic recording medium, high-performance electromagnetic and spintronic devices. [14][15][16] Electrospinning is a method for the preparation of one-dimensional nanofibers with large aspect ratio and uniform diameter. [17,18] As a raw material, one-dimensional nanofibers are widely used for designing and constructing products with twodimensional and three-dimensional structures.…”

Properties of Zirconium Oxide and Cobalt Ferrite Layered Nanocomposite

“…17 Cobalt ferrite in thin film form has also been prepared by spray pyrolysis using cobalt and iron nitrate precursors. 18 Magnetization-field or Kerr loops with certain coercive force has earlier been recorded in CoFe 2 O 4 particles [3][4][5][6]8,10,14,16 and thin films, 18 in most cases at room temperature. Ferromagnetic CoFe 2 O 4 particles have been added to YBa 2 Cu 3 O 7-δ thin films to enhance flux pinning in potentially superconducting materials which, however, led to the formation of Y(Fe,Co)O 3 , leaving the host material yttrium-deficient.…”

“…1 Cobalt-iron-oxygen ternary system has been of considerable interest, driven perhaps by the necessity of use it as a constituent compound in more complex structures exploited in solid oxide fuel cells. 2 Cobalt ferrite has been studied 3 as an attractive magnetic material suited to magneto-optical recording, integrated optics, or waveguides, due to its potential combination of semiconducting and magnetic properties including high coercivity, anisotropy, and magnetostriction.…”

“…3 Regarding other 3D structures based on cobalt ferrite, Co x Fe 3−x O 4 magnetic thin films have been grown on the pore walls of alumina membranes by atomic layer deposition. 17 Cobalt ferrite in thin film form has also been prepared by spray pyrolysis using cobalt and iron nitrate precursors.…”