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C. de Julián Fernández and F. Pineider
Currently, different plasmonic diagnostic and sensing devices or platforms, using
LSPR effects, are under investigation. MP NPs are gathering interest due to the possibility to combine the plasmonic application and an improvement in the efficiency
to separate, concentrate or localize the analyte thanks to magnetic control in such
a way to increase the sensibility, selectivity and detection rate. On the other hand,
MO effects are being considered for the detection method. Recently, MCD and Kerr
effects have been demonstrated to be high performance techniques for optical sensing
of non-magnetic plasmonic structures [229]. However, since the MO signal of the
magnetic materials is larger than that of the plasmonic ones and it can be reached
applying smaller magnetic fields, the performance of magnetic structures should be
better. On the other hand, MO spectroscopy could be useful to improve the selectivity
of optical detection. Taking advantage of the phase change of the MO signal near
the SPR proposed in [259], Macaferri et al. [260] developed an ultrasensitive and
label-free molecular-level detection using ellipsoidal Ni nanodiscs and Kerr effect
detection.
The employment of MP nanostructures for optimizing catalytic processes is
another interesting application for magnetic-plasmonic hybrid structures. Most of
the investigations exploit the bifunctionality of these structures, using for instance
the capability of magnetic concentration, or the functionalization of the plasmonic
surface. However, new scenarios that benefit from the properties of these hybrid
structures are becoming clear: in hybrid structures like Au@Fe-oxides, the charge
transfer mechanism and the charge depletion region can modulate the surface charge
for catalytic reactions [90, 261–263]. On the other hand, plasmon-mediated catalytic
processes are activated thanks to the local heat induced at the resonance [137].
In the case of MP NPs, the combination of photothermal and magnetic induced
hyperthermia can be a new approach for controlling catalytic processes.
Another interesting perspective regards spin-plasmonics, i.e. the effects correlated
to the net spin-polarization of the electrons involved in the plasmonic excitations. The
spin polarization of s-band should not occur in pure plasmonic materials since they are
diamagnetic, while it occurs in the s and d bands at the Fermi lever of the magnetic
metals. In these materials, the spin-unbalance of s-electrons at the Fermi level is
much smaller than the one corresponding to localized d-electrons. Several experiments based on X-Ray Magnetic Circular Dichroism spectroscopy have demonstrated the possibility to magnetize plasmonic elements. This has been observed in
MPs metallic alloy based nanoparticles, like in AuFe [26, 27] NPs, or in metal@
oxide hybrid heterostructures like Au@Fe 3 O 4 CS NPs [89] as previously discussed.
In magnetic materials, different intrinsic and extrinsic spin scattering mechanisms
can give rise to different magneto-transport effects which are the base of magnetoresistance sensors and other spintronic devices. The effects due to a spin population
and the spin scattering process in the SPR resonance has not been considered at the
moment.
The landscape of new effects and applications of Magneto-plasmonic materials that is progressively appearing shows an increasing crossover of the MP
effects with thermal effects. Several cases were discussed above in which
magnet/plasmon/thermal effects are correlated, in particular to the photothermal
C. de Julián Fernández and F. Pineider
Currently, different plasmonic diagnostic and sensing devices or platforms, using
LSPR effects, are under investigation. MP NPs are gathering interest due to the possibility to combine the plasmonic application and an improvement in the efficiency
to separate, concentrate or localize the analyte thanks to magnetic control in such
a way to increase the sensibility, selectivity and detection rate. On the other hand,
MO effects are being considered for the detection method. Recently, MCD and Kerr
effects have been demonstrated to be high performance techniques for optical sensing
of non-magnetic plasmonic structures [229]. However, since the MO signal of the
magnetic materials is larger than that of the plasmonic ones and it can be reached
applying smaller magnetic fields, the performance of magnetic structures should be
better. On the other hand, MO spectroscopy could be useful to improve the selectivity
of optical detection. Taking advantage of the phase change of the MO signal near
the SPR proposed in [259], Macaferri et al. [260] developed an ultrasensitive and
label-free molecular-level detection using ellipsoidal Ni nanodiscs and Kerr effect
detection.
The employment of MP nanostructures for optimizing catalytic processes is
another interesting application for magnetic-plasmonic hybrid structures. Most of
the investigations exploit the bifunctionality of these structures, using for instance
the capability of magnetic concentration, or the functionalization of the plasmonic
surface. However, new scenarios that benefit from the properties of these hybrid
structures are becoming clear: in hybrid structures like Au@Fe-oxides, the charge
transfer mechanism and the charge depletion region can modulate the surface charge
for catalytic reactions [90, 261–263]. On the other hand, plasmon-mediated catalytic
processes are activated thanks to the local heat induced at the resonance [137].
In the case of MP NPs, the combination of photothermal and magnetic induced
hyperthermia can be a new approach for controlling catalytic processes.
Another interesting perspective regards spin-plasmonics, i.e. the effects correlated
to the net spin-polarization of the electrons involved in the plasmonic excitations. The
spin polarization of s-band should not occur in pure plasmonic materials since they are
diamagnetic, while it occurs in the s and d bands at the Fermi lever of the magnetic
metals. In these materials, the spin-unbalance of s-electrons at the Fermi level is
much smaller than the one corresponding to localized d-electrons. Several experiments based on X-Ray Magnetic Circular Dichroism spectroscopy have demonstrated the possibility to magnetize plasmonic elements. This has been observed in
MPs metallic alloy based nanoparticles, like in AuFe [26, 27] NPs, or in metal@
oxide hybrid heterostructures like Au@Fe 3 O 4 CS NPs [89] as previously discussed.
In magnetic materials, different intrinsic and extrinsic spin scattering mechanisms
can give rise to different magneto-transport effects which are the base of magnetoresistance sensors and other spintronic devices. The effects due to a spin population
and the spin scattering process in the SPR resonance has not been considered at the
moment.
The landscape of new effects and applications of Magneto-plasmonic materials that is progressively appearing shows an increasing crossover of the MP
effects with thermal effects. Several cases were discussed above in which
magnet/plasmon/thermal effects are correlated, in particular to the photothermal