Magneto-optical methods for magnetoplasmonics in noble metal nanostructures

Abstract

The use of magneto-optical techniques to tune the plasmonic response of nanostructures is a hot topic in active plasmonics, with fascinating implications for several plasmon-based applications and devices. For this emerging field, called magnetoplasmonics, plasmonic nanomaterials with strong optical response to magnetic field are desired, which is generally challenging to achieve with pure noble metals. To overcome this issue, several efforts have been carried out to design and tailor the magneto-optical response of metal nanostructures, mainly by combining plasmonic and magnetic materials in a single nanostructure. In this tutorial we focus our attention on magnetoplasmonic effects in purely plasmonic nanostructures, as they are a valuable model system allowing for an easier rationalization of magnetoplasmonic effects. The most common magneto-optical experimental methods employed to measure these effects are introduced, followed by a review of the major experimental observations that are discussed within the framework of an analytical model developed for the rationalization of magnetoplasmonic effects. Different materials are discussed, from noble metals to novel plasmonic materials, such as heavily doped semiconductors.

Magnetic Circular Dichroism Responses with High Sensitivity and Enhanced Spectral Resolution in Multipolar Plasmonic Modes of Silver Nanoparticles with Dimensions between 90 and 200 nm

“…In other words, in addition to the very broad derivative-like signals of the dipolar plasmonic mode, superposition of quadrupolar and higher-order resonances made the responses very complicated. Then, to better understand the MCD features of the respective plasmonic modes, simultaneous deconvolutions of both extinction and MCD spectra were representatively conducted for sample G-8 , since the MCD arises from the same excitations as those seen in the optical extinction . The main focus of this analysis is to clearly resolve a bisignate MCD nature for the dipolar and quadrupolar modes as well as a monosignate character for the octupolar mode.…”

“…Then, to better understand the MCD features of the respective plasmonic modes, simultaneous deconvolutions of both extinction and MCD spectra were representatively conducted for sample G-8, since the MCD arises from the same excitations as those seen in the optical extinction. 21 The main focus of this analysis is to clearly resolve a bisignate MCD nature for the dipolar and quadrupolar modes as well as a monosignate character for the octupolar mode. The spectral fits of extinction and MCD (obtained under the N-to-S direction) spectra are shown in Figure 4a and c or d, respectively, and the deconvoluted four plasmonic MCD components are shown in Figure 4b.…”

“…This suggests the possibility of a highly asymmetric profile of the MCD response. The situation can be achieved when the octupolar plasmonic resonance as one of the dark modes also has different excitation efficiencies between the LCPL and the RCPL. , If so, within the size range examined, a sharper peak would result in a larger MCD signal, , giving high sensitivity and enhanced spectral resolution in the dark (octupolar) mode. In any case, MCD is expected to provide key information on higher-order magnetoplasmonic modes of various nanostructures with very high sensitivity and enhanced spectral resolution.…”

“…When one more highly symmetric derivative-shaped MCD response (component 5) was additionally included in the fitting, a better-reproduced MCD profile could be obtained, as shown in Figure 4d. Note here that the extinction spectrum (typically for a nanosphere) should ideally be composed of Lorentzian functions, 3,21 but in the present case, the Gaussian nature of the peaks for dipolar and quadrupolar plasmon modes is observed, which can substantially be attributed to the size/shape inhomogeneity, so the bisignate MCD curve and the corresponding extinction profile (component 1 or 2) were phenomenologically made by the difference and sum of a single set of Gaussian profiles, respectively. 13,17 According to the analysis, broad extinction bands 1 and 2 (Figure 4a), assigned as the dipolar and quadrupolar polarization modes, respectively, can give rise to derivativelike MCD components 1 and 2 (Figure 4b).…”

Longitudinal Magneto-Optical Kerr Effect of Nanoporous CoFeB and W/CoFeB/W Thin Films

“…Apart from various heterogeneous structures, including distributed periodic systems, lumped systems, irregular and coupled waveguide systems, and controlled magnetic structures, which are available for data processing and storage in the microwave range [1], the magneto-optical Kerr effect (MOKE) describing the linearly polarized light rotation of the reflection and the relative changes in reflectivity [2][3][4] has been intensively used in optical and magnetic data storage, domain observation [5,6], optical isolators, and fast optical modulation [7,8]. Recently, with the acquisition of high sensing performance in small molecules at low concentrations, MOKE has been widely investigated to enhance the sensing performance on the gas detection [9,10], liquid detection [11][12][13], magnetometry, 2 of 15 magnetic phase probes [14][15][16], and magnetic biosensing [17][18][19][20][21] due to its higher figure of merit (FOM) and sensitivity (they are comprehensive parameters for evaluating sensor performance) than conventional optical-mode or magnetic-mode methods.…”