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C. de Julián Fernández and F. Pineider
give rise to the damping of the plasmonic properties in the different nanostructures.
Alternatively, more transparent magnetic materials, like magnetic garnets (YIG) or
magnetic metal-doped semiconductors, like ferromagnetic Co doped ZnO [237] or
paramagnetic CeF 3 [238] are known, but their synthesis as nanoparticles or similar
is currently a challenge. In this case, a more promising design would be the synthesis
of metallic multicomponent alloys, semiconductors or multicomponent oxides in
which the optical, plasmonic and magnetic properties could be optimized thanks to
the control of the composition. Also, the search of alternative plasmonic materials
should be interesting to develop MP nanostructures, since the vastly employed Ag and
Au are not fully optimal materials [10]. For example, even if Ag has low optical losses
in the visible optical range, the nanoparticles are not stable as Ag oxidizes easily. Au
is more chemically stable, but it has large losses. These metals have large absorption
in the NIR region where many applications—like telecommunications (TC) and
biomedicine—are now working. Strong research activity is currently focused on
novel plasmonic materials [9] and the development of MP structures with these
compounds will be interesting.
The previous question is crucial also for the development of MP-based magnetooptical devices. In fact, the magneto-optical figure of merit, i.e. the parameter that
defines the efficiency of a material for MO applications, is inversely proportional to
the absorption. Magnetic garnets and Eu-chalcogenides, that have smaller MO signal
than Fe or Co metals, are however employed in optical telecom devices due to their
small losses in the Vis and IR [14]. The synthesis of MP NPs with materials with
better transparency, as was previously discussed, or the employment of magnetic
materials with high MO properties as half-metallic or Heusler phases [240] holds
great promise. However, the synthesis of nanoparticles of these materials has not been
developed at the moment. An alternative is the design of single phase and hybrid MP
NPs with a morphology in which MO and SPR signals are not directly coupled.
For example, in asymmetric structures, like ellipsoidal discs, the main SPR and the
plasmon MO resonance occurs at different energies as are correlated with different
orientations of discs. As shown by Chen et al. [241] in ellipsoidal Ni discs or by
Macaferri et al. [242] in ellipsoids while the optical SPR can be excited along the
main axis of the ellipsoid, the plasmonic MO excitation occurs along the orthogonal
short axis at different wavelength. On the other hand, similar gap between MO and
SPR has been observed in 2D arrays in which a mixture of plasmonics (Au) and
magnetic (Ni) discs are arranged. Depending on the relative orientation of light and
the array structure, different dipolar coupling processes between the plasmonic and
magnetic discs (Ni–Ni and Au–Ni) are possible [243, 244], giving rise to high MO
signal in a low absorption regime. Theoretical studies show that the development of
MP photonic crystals composed of mixtures or single NPs could give rise to high
magneto-optical performances.
Directly correlated with MO effects is the use of MPs for magnetic storage technologies [245, 246]. Heat Assisted Magnetic Recording (HARM) [247] is a commercial technology that takes advantage of the interplay between magnetic and plasmonic
units to reach record (2 Tb/in.
2 ) density of magnetic storage [248]. This technology
employs ultrafast switching of the magnetization of bits thanks to the local heating
C. de Julián Fernández and F. Pineider
give rise to the damping of the plasmonic properties in the different nanostructures.
Alternatively, more transparent magnetic materials, like magnetic garnets (YIG) or
magnetic metal-doped semiconductors, like ferromagnetic Co doped ZnO [237] or
paramagnetic CeF 3 [238] are known, but their synthesis as nanoparticles or similar
is currently a challenge. In this case, a more promising design would be the synthesis
of metallic multicomponent alloys, semiconductors or multicomponent oxides in
which the optical, plasmonic and magnetic properties could be optimized thanks to
the control of the composition. Also, the search of alternative plasmonic materials
should be interesting to develop MP nanostructures, since the vastly employed Ag and
Au are not fully optimal materials [10]. For example, even if Ag has low optical losses
in the visible optical range, the nanoparticles are not stable as Ag oxidizes easily. Au
is more chemically stable, but it has large losses. These metals have large absorption
in the NIR region where many applications—like telecommunications (TC) and
biomedicine—are now working. Strong research activity is currently focused on
novel plasmonic materials [9] and the development of MP structures with these
compounds will be interesting.
The previous question is crucial also for the development of MP-based magnetooptical devices. In fact, the magneto-optical figure of merit, i.e. the parameter that
defines the efficiency of a material for MO applications, is inversely proportional to
the absorption. Magnetic garnets and Eu-chalcogenides, that have smaller MO signal
than Fe or Co metals, are however employed in optical telecom devices due to their
small losses in the Vis and IR [14]. The synthesis of MP NPs with materials with
better transparency, as was previously discussed, or the employment of magnetic
materials with high MO properties as half-metallic or Heusler phases [240] holds
great promise. However, the synthesis of nanoparticles of these materials has not been
developed at the moment. An alternative is the design of single phase and hybrid MP
NPs with a morphology in which MO and SPR signals are not directly coupled.
For example, in asymmetric structures, like ellipsoidal discs, the main SPR and the
plasmon MO resonance occurs at different energies as are correlated with different
orientations of discs. As shown by Chen et al. [241] in ellipsoidal Ni discs or by
Macaferri et al. [242] in ellipsoids while the optical SPR can be excited along the
main axis of the ellipsoid, the plasmonic MO excitation occurs along the orthogonal
short axis at different wavelength. On the other hand, similar gap between MO and
SPR has been observed in 2D arrays in which a mixture of plasmonics (Au) and
magnetic (Ni) discs are arranged. Depending on the relative orientation of light and
the array structure, different dipolar coupling processes between the plasmonic and
magnetic discs (Ni–Ni and Au–Ni) are possible [243, 244], giving rise to high MO
signal in a low absorption regime. Theoretical studies show that the development of
MP photonic crystals composed of mixtures or single NPs could give rise to high
magneto-optical performances.
Directly correlated with MO effects is the use of MPs for magnetic storage technologies [245, 246]. Heat Assisted Magnetic Recording (HARM) [247] is a commercial technology that takes advantage of the interplay between magnetic and plasmonic
units to reach record (2 Tb/in.
2 ) density of magnetic storage [248]. This technology
employs ultrafast switching of the magnetization of bits thanks to the local heating