CoFe2O4 and CoFe2O4‐SiO2 Nanoparticle Thin Films with Perpendicular Magnetic Anisotropy for Magnetic and Magneto‐Optical Applications. (8th February 2016)

• Record Type: Journal Article
• Authors: Erdem, Derya; Bingham, Nicholas S.; Heiligtag, Florian J.; Pilet, Nicolas; Warnicke, Peter; Heyderman, Laura J.; Niederberger, Markus
• Is Part Of: Advanced functional materials. Volume 26:Number 12(2016)
• Page Start: 1954
• Page End: 1963
• Publication Date: 2016-02-08
• Subjects: cobalt ferrite -- microwave synthesis -- nanocomposite -- nanoparticles -- nonaqueous sol‐gel -- perpendicular magnetic anisotropy -- thin films; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adfm.201504538
• Languages: English
• ISSNs: 1616-301X

Abstract

Abstract : This paper presents an efficient colloidal approach to process CoFe2 O4 and SiO2 nanoparticles into thin films for magnetic and magneto‐optical applications. Thin films of varying CoFe2 O4 ‐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 CoFe2 O4 films reveal a superparamagnetic behavior with both Co 2+ and Fe 3+ contributing to the magnetism. Polar Kerr measurements show the presence of a spontaneous magnetization in the CoFe2 O4 and CoFe2 O4 ‐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 CoFe2 O4 . Abstract : Thin films for magnetic and magneto‐optical applications are prepared from CoFe2 O4 and SiO2 nanoparticle dispersions. Variation of the CoFe2 O4 ‐to‐SiO2 ratio enabled the fine‐tuning of the optical and magneto‐optical properties. In‐plane tensile stresses associated with constrained sintering conditions resulted in perpendicular magnetic anisotropy.