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C. de Julián Fernández and F. Pineider
is metallic several studies show that these CS structures exhibit a single plasmonic
peak that is red shifted and broader as the percentage of magnetic moiety is larger
but also blue shift by modifying the size of the magnetic moiety [38]. The study by
López-Ortega et al. [51] obtains a reasonable agreement of the plasmonic properties
of Ag@CoFe CS with the simulations.
Previous discussions on the plasmonic properties of the hybrid systems considered
a static description of the plasmon resonance, i.e. the solution of Maxwell’equations
of the system. However, the dynamics of the plasmons needs also to be considered
[52]. Only few different pump and probe studies [53–56] have been performed on Au–
Fe oxide HDs and other morphologies, showing that the plasmon resonance is characterized by a faster electron relaxation process than that of bare Au NPs. Considering
the previous described experiments on magnetic metal-plasmonic heterostructures
(CoFe–Ag [38] and Ag@CoFe [51]), the hypothesis of a charge-transfer process
from the plasmonic to the magnetic moiety can be proposed. Cosmin et al. [56],
in contrast, proposed that the observed relaxation is due to the spill-out of electron density from gold electron at the gold/magnetic interface excluding a charge
transfer mechanism. Further studies are required considering a controlled interface
and chemical states of the magnetic oxide.
Composites or mixtures of isolated magnetic and plasmonic particles are the
simplest MP systems. A large variety of materials have been synthesized: micro
and nano capsules containing a mixture of the two classes of NPs [35]; capsules
containing only one kind of nanomaterial, magnetic for example, that are decorated
by the plasmonic counterpart [57, 58]; multilayers or onion-like particles in which
plasmonic and magnetic moieties are separated by a dielectric layer like SiO 2 or
TiO 2 [41, 59–66]. MP effects have been investigated even in mixtures or simple
solutions containing the two types of NPs [67, 68]. In all these cases, the interparticle dipolar electromagnetic interactions and the absorption of the magnetic NPs
determine the changes of the plasmonic resonance respect to bare plasmonic nanoparticles. Depending on the interparticle distance, the geometry of the particles and the
magnetic/plasmonic nanoparticle concentration ratio, the coupling can have different
strength. In very diluted systems the dielectric contribution of the magnetic moiety
could be included in the term of the dielectric medium (ε m ) using a mean-field
model [68, 69]. However, SPR should be calculated considering that the medium
surrounding the plasmonic particles is absorbent [69–71]. A red shift and damping
of the LSPR is expected as previously discussed. If interparticle distance is small
(nanometers), strong confinement of the EMF occurs, and the so called “hot spots”,
can be present even between plasmonic and metallic magnetic nanoparticles [72,
73]. This can give rise to blue shift of the LSPR. Finally, superstructures composed
by networks of the two classes of materials have been also synthesized [74, 75].
Also magnetic properties of the MP structures appear different compared to equivalent bare magnetic particles, even if plasmonic materials are diamagnetic. In first
instance, the hybrid nature of MP structures determines that the growth mechanism is
different to that of bare magnetic nanoparticles. For example, the synthesis of hybrid
structures like CS and HDs requires a two-step process in which heteronucleation
C. de Julián Fernández and F. Pineider
is metallic several studies show that these CS structures exhibit a single plasmonic
peak that is red shifted and broader as the percentage of magnetic moiety is larger
but also blue shift by modifying the size of the magnetic moiety [38]. The study by
López-Ortega et al. [51] obtains a reasonable agreement of the plasmonic properties
of Ag@CoFe CS with the simulations.
Previous discussions on the plasmonic properties of the hybrid systems considered
a static description of the plasmon resonance, i.e. the solution of Maxwell’equations
of the system. However, the dynamics of the plasmons needs also to be considered
[52]. Only few different pump and probe studies [53–56] have been performed on Au–
Fe oxide HDs and other morphologies, showing that the plasmon resonance is characterized by a faster electron relaxation process than that of bare Au NPs. Considering
the previous described experiments on magnetic metal-plasmonic heterostructures
(CoFe–Ag [38] and Ag@CoFe [51]), the hypothesis of a charge-transfer process
from the plasmonic to the magnetic moiety can be proposed. Cosmin et al. [56],
in contrast, proposed that the observed relaxation is due to the spill-out of electron density from gold electron at the gold/magnetic interface excluding a charge
transfer mechanism. Further studies are required considering a controlled interface
and chemical states of the magnetic oxide.
Composites or mixtures of isolated magnetic and plasmonic particles are the
simplest MP systems. A large variety of materials have been synthesized: micro
and nano capsules containing a mixture of the two classes of NPs [35]; capsules
containing only one kind of nanomaterial, magnetic for example, that are decorated
by the plasmonic counterpart [57, 58]; multilayers or onion-like particles in which
plasmonic and magnetic moieties are separated by a dielectric layer like SiO 2 or
TiO 2 [41, 59–66]. MP effects have been investigated even in mixtures or simple
solutions containing the two types of NPs [67, 68]. In all these cases, the interparticle dipolar electromagnetic interactions and the absorption of the magnetic NPs
determine the changes of the plasmonic resonance respect to bare plasmonic nanoparticles. Depending on the interparticle distance, the geometry of the particles and the
magnetic/plasmonic nanoparticle concentration ratio, the coupling can have different
strength. In very diluted systems the dielectric contribution of the magnetic moiety
could be included in the term of the dielectric medium (ε m ) using a mean-field
model [68, 69]. However, SPR should be calculated considering that the medium
surrounding the plasmonic particles is absorbent [69–71]. A red shift and damping
of the LSPR is expected as previously discussed. If interparticle distance is small
(nanometers), strong confinement of the EMF occurs, and the so called “hot spots”,
can be present even between plasmonic and metallic magnetic nanoparticles [72,
73]. This can give rise to blue shift of the LSPR. Finally, superstructures composed
by networks of the two classes of materials have been also synthesized [74, 75].
Also magnetic properties of the MP structures appear different compared to equivalent bare magnetic particles, even if plasmonic materials are diamagnetic. In first
instance, the hybrid nature of MP structures determines that the growth mechanism is
different to that of bare magnetic nanoparticles. For example, the synthesis of hybrid
structures like CS and HDs requires a two-step process in which heteronucleation