Magnetic-plasmonic properties of CoFe2O4@Au nanocomposite

Abstract

Cobalt ferrite-gold nanocomposite (CoFe2O4@Au), were synthesized using for the first time the synthetic route that involved (i) the polyol method to produce cobalt ferrite nanoparticles (CoFe2O4), (ii) the surface of CoFe2O4 functionalized with APTES to obtain amino groups, (iii) decorated cobalt ferrite nanoparticles with the ultra-small gold nanoparticles produced by the reduction of THPC, and (iv) using the platy solution method whereby the CoFe2O4 nanoparticles were decorated with a gold shell through crystal growth. X-ray diffraction (XRD) experiments showed that CoFe2O4 particles crystallized in a spinel structure (6 nm diameter). The XRD experiments for CoFe2O4@Au nanocomposite showed the presence of cubic gold nanocrystals confirming the presence of gold. Further experiments conducted using Fourier-transformed infrared (FTIR) spectroscopy showed the typical bands observed for the coordination around the tetrahedral and octahedral sites of CoFe2O4 particles. The evolution of the synthesis was also tracked through FTIR by observing the peaks attributed to the silica stretching bands on the surface of the APTES functionalized CoFe2O4 nanoparticles and the displacement of the ferrite peaks suggest the gold shell on the surface of the cobalt ferrite nanoparticles throughout the nanocomposite. UV–Vis spectroscopy showed a red shift in the spectra for CoFe2O4@Au when compared to spectra produced for CoFe2O4. Transmission electron microscope (TEM) images were obtained for both CoFe2O4 nanoparticles and CoFe2O4@Au nanocomposite. The images showed a difference in the size of the particles after the formation of the nanocomposite. Physical property measurements (PPMS) were performed to study the magnetic properties for both newly synthesized gold-coated nanocomposite and those without the gold. The study revealed superparamagnetic behavior for both samples and demonstrated that the addition of the Au shell has no influence on the block temperature, thus the particle growth is due to the gold coating. The magnetic properties were further examined using the Langevin model. This study found that the plasmonic gold behavior did not alter the magnetic properties of the particles and that instead the magnetic properties of CoFe2O4@Au are maintained which can be useful to magnetic-plasmonic applications.