Monodisperse cobalt ferrite nanomagnets with uniform silica coatings.
Ferro- and ferrimagnetic nanoparticles are difficult to manipulate in solution as a consequence of the formation of magnetically induced nanoparticle aggregates, which hamper the utility of these particles for applications ranging from data storage to bionanotechnology. Nonmagnetic shells that encapsulate these magnetic particles can reduce the interparticle magnetic interactions and improve the dispersibility of the nanoparticles in solution. A route to create uniform silica shells around individual cobalt ferrite nanoparticles--which uses poly(acrylic acid) to bind to the nanoparticle surface and inhibit nanoparticle aggregation prior to the addition of a silica precursor--was developed. In the absence of the poly(acrylic acid) the cobalt ferrite nanoparticles irreversibly aggregated during the silica shell formation. The thickness of the silica shell around the core-shell nanoparticles could be controlled in order to tune the interparticle magnetic coupling as well as inhibit magnetically induced nanoparticle aggregation. These ferrimagnetic core-silica shell structures form stable dispersion in polar solvents such as EtOH and water, which is critical for enabling technologies that require the assembly or derivatization of ferrimagnetic particles in solution.
Dai
Qiu
Q
IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, United States.
Lam
Michelle
M
Swanson
Sally
S
Yu
Rui-Hui Rachel
RH
Milliron
Delia J
DJ
Topuria
Teya
T
Jubert
Pierre-Olivier
PO
Nelson
Alshakim
A
D003035:Cobalt / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D008280:Magnetics; D046529:Microscopy, Electron, Transmission; D049329:Nanostructures / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013818:Thermogravimetry
D005290:Ferric Compounds; C001215:ferrite; D003035:Cobalt; D012822:Silicon Dioxide