5 Magneto-Plasmonic Nanoparticles
127
produced by plasmon induced confinement of light. This is obtained by coupling a
plasmonic antenna to a continuous magnetic medium [197]. Alternatively, all-optical
magnetic recording has also been proposed as an ultrafast technology in the THz
regime to switching the magnetization in magnetic memory and logic spintronic
devices [250–253]. Ultrafast and high-power laser pulses allow magnetic erasing
and writing processes thanks to a phenomenon known as the inverse Faraday effect.
The incorporation of plasmonic structures should enhance the EMFs while at the
same time allowing subwavelength spatial resolution inverse Faraday effects [251,
254, 255] and hence facilitate the incorporation of this technology in the on-chip
submicrometric devices. While these two technologies are now investigated in films,
3D dots will be the further progress technology—for example, heated dot magnetic
recording (HDMR) promises up to 10 Tb/in.
2 [256]. Some works have investigated
the possibility of MO writing and reading employing MP multilayer dots [255].
Here the aim is to overcome the limit of magneto-optical imaging in terms of spatial
resolution [246]. MP nanoparticles should be the prototypes to investigate future
developments of these technologies.
While the former technology (HAMR) takes advantage of the heat-induced
demagnetization process, a different type of photo-induced switching mechanism
activated by plasmonic resonance was proposed in Bogani et al. [257]. In this study
the MO-detected hysteresis loops of AuFe nanoparticles with high coercive field
were measured under the simultaneous irradiation with low power light at different
wavelengths. The authors observed a faster magnetic relaxation of the nanoparticles
when irradiating at the SPR wavelength. Different tests excluded that the observed
phenomena were due to plasmon induced thermal or inverse Faraday effects. The
authors propose that spin scattering processes are activated by the plasmon-induced
electronic excitations.
Another field in which the multifunctional capabilities of MP NPs are very
attractive is that of biomedical applications [246]. The development of theranostic
approaches, i.e. diagnostic, imaging and therapeutic capabilities on a single platform
for efficient and personalized treatment of cancer and other diseases, is a field in
which the combination of the different performances of the plasmonics and magnetic
moieties of the MP NPs can bring significant momentum. The benefit is also the possibility of overcoming the natural limits of each technique: the red-shift of SPR of the
MP NPs allows imaging and treatment using IR radiation, while radio frequencyinduced hyperthermia allows to perform thermal therapy in deeper regions of the
body, unreachable to light, or to increase local temperature combining magneto- and
photo-thermia. First demonstrations have been shown [258]; however, one of the
main limitations for these applications is the restriction to Au for plasmonic and Fe
oxide for the magnetic moiety taking into account cytotoxicity criteria. On the other
hand, Ag has a stronger and narrower SPR compared to Au, while the Co-ferrite
or FeCo alloys have larger anisotropy and magnetization respectively than the Fe
oxides. However, these better compounds are chemically unstable in the body and
cytotoxic.
127
produced by plasmon induced confinement of light. This is obtained by coupling a
plasmonic antenna to a continuous magnetic medium [197]. Alternatively, all-optical
magnetic recording has also been proposed as an ultrafast technology in the THz
regime to switching the magnetization in magnetic memory and logic spintronic
devices [250–253]. Ultrafast and high-power laser pulses allow magnetic erasing
and writing processes thanks to a phenomenon known as the inverse Faraday effect.
The incorporation of plasmonic structures should enhance the EMFs while at the
same time allowing subwavelength spatial resolution inverse Faraday effects [251,
254, 255] and hence facilitate the incorporation of this technology in the on-chip
submicrometric devices. While these two technologies are now investigated in films,
3D dots will be the further progress technology—for example, heated dot magnetic
recording (HDMR) promises up to 10 Tb/in.
2 [256]. Some works have investigated
the possibility of MO writing and reading employing MP multilayer dots [255].
Here the aim is to overcome the limit of magneto-optical imaging in terms of spatial
resolution [246]. MP nanoparticles should be the prototypes to investigate future
developments of these technologies.
While the former technology (HAMR) takes advantage of the heat-induced
demagnetization process, a different type of photo-induced switching mechanism
activated by plasmonic resonance was proposed in Bogani et al. [257]. In this study
the MO-detected hysteresis loops of AuFe nanoparticles with high coercive field
were measured under the simultaneous irradiation with low power light at different
wavelengths. The authors observed a faster magnetic relaxation of the nanoparticles
when irradiating at the SPR wavelength. Different tests excluded that the observed
phenomena were due to plasmon induced thermal or inverse Faraday effects. The
authors propose that spin scattering processes are activated by the plasmon-induced
electronic excitations.
Another field in which the multifunctional capabilities of MP NPs are very
attractive is that of biomedical applications [246]. The development of theranostic
approaches, i.e. diagnostic, imaging and therapeutic capabilities on a single platform
for efficient and personalized treatment of cancer and other diseases, is a field in
which the combination of the different performances of the plasmonics and magnetic
moieties of the MP NPs can bring significant momentum. The benefit is also the possibility of overcoming the natural limits of each technique: the red-shift of SPR of the
MP NPs allows imaging and treatment using IR radiation, while radio frequencyinduced hyperthermia allows to perform thermal therapy in deeper regions of the
body, unreachable to light, or to increase local temperature combining magneto- and
photo-thermia. First demonstrations have been shown [258]; however, one of the
main limitations for these applications is the restriction to Au for plasmonic and Fe
oxide for the magnetic moiety taking into account cytotoxicity criteria. On the other
hand, Ag has a stronger and narrower SPR compared to Au, while the Co-ferrite
or FeCo alloys have larger anisotropy and magnetization respectively than the Fe
oxides. However, these better compounds are chemically unstable in the body and
cytotoxic.