Theoretical calculation of absorption properties of NiFe@Au core-shell nanoparticles

The multimetallic nanostructures of a noble metal such as gold, silver, and copper have attracted great attention in alloys and core-shell configuration due to the enhanced plasmonic effect. In this theoretical study, the optical properties of bare NiFe and NiFe@Au core-shell NPs have been calculated using extended Mie theory. The core-size of nanostructures is considered 5 nm to 25 nm and shell thickness systematically varied as 3, 5, 7 and 10 nm. It is observed that the localized surface plasmon resonance peaks are red-shifted with increasing shell thickness and blue-shifted with increasing core-sizes. Further, broadening in LSPR peaks is found, as the size of core-NiFe NPs increased and optical efficiency increases with Au-shell thickness. The LSPR peaks at λmax show the absorption spectra in the range of 508-541 nm wavelengths and hence, absorption peaks are found in the visible region. In addition, LSPR peaks of NiFe (permalloy) coated with Au NPs are influenced by changing the refractive index of the embedded medium. Hence, the optical response of NiFe coated with Au nanospheres can be tuned and controlled in the visible region of the electromagnetic spectrum. From the results, it is revealed that varying either NiFe-core or Au-shell thickness and embedded medium could result in obtaining tunable light absorption in UV-visible and may find application in optical imaging, sensing, medical, and novel functional and biomagnetic devices.