The Interparticle Coupling Effect on Plasmon Resonance Properties of Magnetite@Au Magnetoplasmonic Nanoparticles☆

Abstract Magnetoplasmonics based on Composite nanostructure, has been used in sensing, optical devices and optical switching. Magnetite@Au core@shell nanostructure exhibits both plasmonic and magnetic properties and holds promise for using in biomedical applications. The ability to control optical properties of magnetite@Au over a broad spectral range and adjustable composite thickness make these nanostructures an important subject for magnetoplasmonic studies. In this research, interparticle coupling effect on plasmon resonance properties of magnetite@Au magnetoplasmonics nanoparticles by using finite element method has been calculated. In addition optical characteristic of magnetite@Au strongly depend on size, surrounding medium and pitches between the particles. The effects of these parameters on optical properties of magnetite@Au nanostructures have been studied. The calculated results show plasmon resonance absorption peak has changed from 576 nm to 540 nm by decreasing size of Au coating from 5 nm to 17 nm. Moreover, by increasing magnetite core diameter from 10 nm to 25 nm, wavelength of maximum plasmon resonance absorption has been changed 590 nm to 620 nm. As the refractive index of medium around magnetite@Au increasing, results have shown a red shift absorption peak which the peak position linearly depends on the refractive index of medium. The effects of coupling between two magnetite@Au core@shell on plasmon resonance peak have been calculated. The results demonstrate when magnetite@Au nanoparticles pitches are shorter than the surface plasmon attenuation length, the surface plasmons couple to each other, thus it is creating new modes that differs from the usual dispersion relation of suface plasmons. Therefore, simulated results have showed wavelength of maximum absorption for coupled magnetite@Au at 506 nm which is different from single magnetite@Au core-shell and demonstrates about 80 nm blue shift. These results could be employed for design of plasmonic sensors with tunable optical properties especially with interparticle coupling in presence of magnetic field.