5 Magneto-Plasmonic Nanoparticles
121
expected in such a way to get a better understanding of biomedical systems and an
accurate anatomical and functional information from inside the body and in bio-tests.
MP nanostructures can be considered for multiple theranosticapproaches in
biomedicine [187, 188] (Fig. 5.4ii). Theranostics considers the simultaneous or
consecutive combination of diagnostic and therapeutic methods for a personalized,
faster and efficient medical treatment. Independently, both plasmonics and magnetic
nanoparticles, are considered for a theranostic approach mostly focused to cancer
treatments. With MP nanoparticles, a wider range of targeting, diagnostic and therapeutic possibilities is available, as demonstrated the increasing number of studies
[59, 60, 62, 131, 132, 135, 147, 178, 189–193].
5.4 Magneto-Optical Effects in MP Nanoparticles
Considering that the plasmonic phenomenon is mainly an optical effect, the direct
cross-linking between the magnetism and plasmonics is the magneto-optical (MO)
effect [172, 174]. This term describes a wide number of optical phenomena correlated
to the interaction between light and matter in which the properties of light change after
interacting with a magnetic material or any material under a magnetic field [194, 195].
In this chapter, we will discuss the main MO linear effects correlated to magnetic
materials: the Faraday effect, Magnetic Circular Dichroism (MCD) and the Kerr
effects. The MCD and the Kerr effect—in transverse configuration—involve changes
in the light absorption, while the Faraday and Kerr effect—in longitudinal and polar
configurations—give rise to the change the polarization of the light producing the
change of the angle of polarization and give rise to an ellipticity. These MO effects
are proportional to the magnetization of the magnetic material and hence change as
a function of applied magnetic field and temperature. In fact, MO can be regarded
also as a magnetometric technique that allows to measure the hysteresis loops of
surfaces, films and also nanoparticles. The information on the magnetic properties
coming from the MO effects depends on the penetration depth of light in matter at
the specific wavelength and can range from some tens of nanometers for metals to
centimeters for magnetic dielectrics (YIG, for example).
MO effects are due to optical transitions that follow the dipole selection rules i.e.
requiring a change of the angular momentum of ±1. Hence MO spectroscopy gives
complementary information to other spectroscopic techniques as MO transitions can
depend on crystal symmetry and spin-electronic structure, in particular concerning
bands split by the Spin–Orbit (SO) coupling [194–196].
These MO effects are incorporated in the description of optical phenomena by
describing the optical properties of the material with a complete dielectric tensor that
includes the non-diagonal magneto-optical terms [14, 19]:
121
expected in such a way to get a better understanding of biomedical systems and an
accurate anatomical and functional information from inside the body and in bio-tests.
MP nanostructures can be considered for multiple theranosticapproaches in
biomedicine [187, 188] (Fig. 5.4ii). Theranostics considers the simultaneous or
consecutive combination of diagnostic and therapeutic methods for a personalized,
faster and efficient medical treatment. Independently, both plasmonics and magnetic
nanoparticles, are considered for a theranostic approach mostly focused to cancer
treatments. With MP nanoparticles, a wider range of targeting, diagnostic and therapeutic possibilities is available, as demonstrated the increasing number of studies
[59, 60, 62, 131, 132, 135, 147, 178, 189–193].
5.4 Magneto-Optical Effects in MP Nanoparticles
Considering that the plasmonic phenomenon is mainly an optical effect, the direct
cross-linking between the magnetism and plasmonics is the magneto-optical (MO)
effect [172, 174]. This term describes a wide number of optical phenomena correlated
to the interaction between light and matter in which the properties of light change after
interacting with a magnetic material or any material under a magnetic field [194, 195].
In this chapter, we will discuss the main MO linear effects correlated to magnetic
materials: the Faraday effect, Magnetic Circular Dichroism (MCD) and the Kerr
effects. The MCD and the Kerr effect—in transverse configuration—involve changes
in the light absorption, while the Faraday and Kerr effect—in longitudinal and polar
configurations—give rise to the change the polarization of the light producing the
change of the angle of polarization and give rise to an ellipticity. These MO effects
are proportional to the magnetization of the magnetic material and hence change as
a function of applied magnetic field and temperature. In fact, MO can be regarded
also as a magnetometric technique that allows to measure the hysteresis loops of
surfaces, films and also nanoparticles. The information on the magnetic properties
coming from the MO effects depends on the penetration depth of light in matter at
the specific wavelength and can range from some tens of nanometers for metals to
centimeters for magnetic dielectrics (YIG, for example).
MO effects are due to optical transitions that follow the dipole selection rules i.e.
requiring a change of the angular momentum of ±1. Hence MO spectroscopy gives
complementary information to other spectroscopic techniques as MO transitions can
depend on crystal symmetry and spin-electronic structure, in particular concerning
bands split by the Spin–Orbit (SO) coupling [194–196].
These MO effects are incorporated in the description of optical phenomena by
describing the optical properties of the material with a complete dielectric tensor that
includes the non-diagonal magneto-optical terms [14, 19]: