Circular dichroism of one-dimensional chain of Au-Fe alloy nanoparticles for refractive index sensing applications

In this paper, we, theoretically , study the optical activity of a linear chain of 40 nm sized in diameter alloy spherical nanoparticles in the presence of a static external magnetic field illuminated by the electromagnetic field of left/right circular polarization in different angles of incidence. Regarding the subwavelength particle size, the coupled dipole method is employed to study the absorption cross section and magnetic circular dichroism (MCD) of the one-dimensional chain. The circular dichroism spectrum reveals that by increasing the Fe percentage in the alloy NPs, the peak intensity of the MCD signal decreases, and the spectrum broadens on the contrary. The refractive index sensitivity of MCD signals is investigated, either. It is shown that MCD signals are more sensitive than plasmonic signals to the refractive index variation. It is shown that the increment in the Fe atomic percentage results in more sensitive signals, as well. As an estimate, the calculations show more than 50% enhancement in the sensitivity of MCD signals of alloy Au 0.85 Fe 0.15 in comparison to plasmonic signals of gold NPs.