5 Magneto-Plasmonic Nanoparticles
117
control of the nanostructural and compositional features is required. On the other
hand, the synergistic behavior between the two moieties has been evidenced investigating other properties and effects. The main case corresponds to the magnetooptical (MO) properties of these materials that will be discussed in the next section.
Another synergistic effect is the observation of a spin and orbital moments in nonmagnetic atoms of alloy-based AuFe nanoparticles [26, 27]. In fact, several studies
have shown the spin polarization of the d and s bands of Au and also Ag elements
when are alloyed with magnetic ones [107, 110–112]. The magnetic moment of these
heavy non-magnetic elements exhibits a large orbital-to-spin ratio as expected due to
their characteristic large spin–orbit coupling. Similar spin polarization of plasmonic
element was observed in Au-Fe 3 O 4 hybrid NPs. In this case, a charge transfer mechanism at the metal-oxide interface could give rise to the spin polarization of Au [89].
This demonstrates other paths of coupling mechanisms between the magnetic and
plasmonic moieties.
5.3 General Applications of MP Nanoparticles
Let us consider first optical applications of MP nanoparticles. In principle, optical
properties of MP NPs follow the same behavior of the plasmonic materials, taking
into account the optical changes induced by the presence of a magnetic moiety. Even
considering the expected resonance shift and spectral broadening, MP NPs exhibit
the same characteristics that allow to design the color, light scattering and contrast,
and optical spectral features required in several photonics and imaging applications
[113–116]. The modification of plasmon resonance under the variation of the environment—a key concept for refractometric sensing devices—has been shown [117–
120]. The strong localization and confinement of light at the SPR, giving rise to
modification of the linear and non-linear optical properties of the capping molecules
or materials is also possible. This is the working principle of many optoelectronics,
sensing and monitoring applications. In particular, Surface-enhanced Raman scattering (SERS) spectroscopy, a spectroscopic technique that uses the plasmon-induced
enhancement of Raman signal to detect a wide variety molecules and compounds,
have been demonstrated both in hybrid MPs systems [121–126] as well in alloybased MPs structures [127–129]. Photo-thermal effects were also demonstrated in
MP nanostructures. This consists in the generation of heat by NPs due to the excitation
of the LSPR and is a well-established subject in applications concerning nanoparticles in biomedicine [130–136] and catalysis [137]. One of the features that has
brought the interest for MP nanostructures is the possibility to tune the SPR down to
the n-IR region. Nowadays, this is a researched property for photonics in telecommunications and biomedical applications. In telecommunications, the scope is the
reduction of losses and the coupling with telecom lasers [9, 10]. The employment of
plasmonic effects and techniques under in-vivo conditions for biomedicine applications is limited by the complete absorption of light in the visible range by the skin
and other bio-tissues [138, 139]. MP NPs can be prepared to exhibit the SPR in the
117
control of the nanostructural and compositional features is required. On the other
hand, the synergistic behavior between the two moieties has been evidenced investigating other properties and effects. The main case corresponds to the magnetooptical (MO) properties of these materials that will be discussed in the next section.
Another synergistic effect is the observation of a spin and orbital moments in nonmagnetic atoms of alloy-based AuFe nanoparticles [26, 27]. In fact, several studies
have shown the spin polarization of the d and s bands of Au and also Ag elements
when are alloyed with magnetic ones [107, 110–112]. The magnetic moment of these
heavy non-magnetic elements exhibits a large orbital-to-spin ratio as expected due to
their characteristic large spin–orbit coupling. Similar spin polarization of plasmonic
element was observed in Au-Fe 3 O 4 hybrid NPs. In this case, a charge transfer mechanism at the metal-oxide interface could give rise to the spin polarization of Au [89].
This demonstrates other paths of coupling mechanisms between the magnetic and
plasmonic moieties.
5.3 General Applications of MP Nanoparticles
Let us consider first optical applications of MP nanoparticles. In principle, optical
properties of MP NPs follow the same behavior of the plasmonic materials, taking
into account the optical changes induced by the presence of a magnetic moiety. Even
considering the expected resonance shift and spectral broadening, MP NPs exhibit
the same characteristics that allow to design the color, light scattering and contrast,
and optical spectral features required in several photonics and imaging applications
[113–116]. The modification of plasmon resonance under the variation of the environment—a key concept for refractometric sensing devices—has been shown [117–
120]. The strong localization and confinement of light at the SPR, giving rise to
modification of the linear and non-linear optical properties of the capping molecules
or materials is also possible. This is the working principle of many optoelectronics,
sensing and monitoring applications. In particular, Surface-enhanced Raman scattering (SERS) spectroscopy, a spectroscopic technique that uses the plasmon-induced
enhancement of Raman signal to detect a wide variety molecules and compounds,
have been demonstrated both in hybrid MPs systems [121–126] as well in alloybased MPs structures [127–129]. Photo-thermal effects were also demonstrated in
MP nanostructures. This consists in the generation of heat by NPs due to the excitation
of the LSPR and is a well-established subject in applications concerning nanoparticles in biomedicine [130–136] and catalysis [137]. One of the features that has
brought the interest for MP nanostructures is the possibility to tune the SPR down to
the n-IR region. Nowadays, this is a researched property for photonics in telecommunications and biomedical applications. In telecommunications, the scope is the
reduction of losses and the coupling with telecom lasers [9, 10]. The employment of
plasmonic effects and techniques under in-vivo conditions for biomedicine applications is limited by the complete absorption of light in the visible range by the skin
and other bio-tissues [138, 139]. MP NPs can be prepared to exhibit the SPR in the