UV-resonant magnetoplasmonic properties of chemically synthesized indium nanoparticles

In this article, we for the first time demonstrate magnetoplasmonic properties of metallic indium (In⁰) nanoparticles, one of the promising non-noble metals for UV plasmonics, by using magnetic circular dichroism (MCD) spectroscopy. In⁰ nanoparticles are synthesized by a kinetically controlled reduction of indium salts, followed by performing centrifugation-based size selection, giving nanoparticles of 37.5 ± 9.7 or 51.6 ± 8.4 nm in diameter. These In⁰ nanoparticles exhibit a single extinction peak in the UV region (<300 nm), which can be attributed to localised surface plasmon resonance (LSPR), and upon increasing the particle size, the peak is red-shifted and broadened. The MCD signatures are then typical for circular magnetoplasmonic modes of metal nanospheres, and on the basis of the MCD responses, the effective mass of an electron (m*) of indium is estimated. Interestingly, although the large-sized In⁰ nanoparticles (51.6 nm) have a broader LSPR linewidth, the magneto-optical (MO) activity is larger than that of the smaller one (37.5 nm), which is unlike the behaviour of Ag nanospheres with high-quality-factor plasmonic performance. This can probably be due not only to the formation of stiff semiconducting (In(OH)₃) shell layers on the In⁰ cores (= In⁰@In(OH)₃ core-shell morphology) but also to the effect of the dielectric function of In⁰ that can influence the light-helicity-dependent field-induced cyclotron shift.