3 Spin-Polarized Plasmonics: Fresh View …
71
3.8 Conclusions
Spin-polarized metals have two channels of conductivity resulted in interesting applications including the most known giant magnetoresistance. Magnetic nanoparticles
have unusual features compared to bulk materials. They manifest superparamagnetic
properties in case of single-domain size. They have discrete density of states due to
quantum size effect. Our experiments with Co nanoparticles clearly show a new type
of plasmon excitation. This type of plasmon has unusual properties due to existence of
two independent groups of electrons with opposite spins providing weak interaction
so that all electron scattering processes occur without spin flip. Magnetic response of
the nanoparticles enables controlled and reversible aggregation accompanied by the
tailoring of optical absorption. Magnetic nature of the nanoparticles suggests a new
type of these plasmons. Magnetic response of Co nanoparticles shows less magnetic
moments per atom relative to the bulk value, namely 0.68 μ b and taking into account
the demagnetization factor 0.96 μ b per atom versus 1.7 μ b . The exchange interaction of electrons splits the energy bands between spin-up electrons and spin-down
electrons. It makes possible to coexist two independent channels of conductivity as
well as two independent plasmons in the same nanoparticle with very different electron relaxation. Indeed, the density of empty states in a partially populated d-band
is high, resulting in a large relaxation rate of the spin-down conduction electrons
and consequently in low quality of the plasmon resonance. In contrast, the majority
electrons with a completely filled d-band do not provide final states for the scattering
processes of the conduction spin-up electrons, therefore supporting a good quality
plasmon resonance. The scattering without spin flip is required to keep these two
plasmons independent.
References
1. P.B. Johnson, R.W. Christy, Optical constants of transition metals: Ti, V, Cr, Mn, Fe Co, Ni,
and Pd. Phys. Rev. 9, 5056 (1974). https://doi.org/10.1103/PhysRevB.9.5056
2. H. Bhata, A.E. Aliev, V.P. Drachev, New mechanism of plasmons specific for spin-polarized
nanoparticles. Sci. Rep. 9, 2019 (2019). https://doi.org/10.1038/s41598-019-38657-w
3. A.R. Young, Chromophores in human skin. Phys. Med. Biol. 42, 789–802 (1997)
4. G.J. Thomas, Raman spectroscopy of protein and nucleic acid assemblies. Annu. Rev. Biophys.
Biomol. Struct. 28, 1–27 (1999)
5. Y. Kumamoto, A. Taguchi, N.I. Smith, S. Kawata, Deep UV resonant Raman spectroscopy for
photodamage characterization in cells. Biomed. Optics Express 2, 927–936 (2011)
6. H. Takeuchi, UV Raman markers for structural analysis of aromatic side chains in proteins.
Anal. Sci. 27, 1077–1086 (2011)
7. L. Ashton, C.E.M. Hogwood, A.S. Tait, J. Kuligowski, C.M. Smales, D.G. Bracewell, A.J.
Dicksone, R. Goodacre, UV resonance Raman spectroscopy: a process analytical tool for host
cell DNA and RNA dynamics in mammalian cell lines. J. Chem. Technol. Biotechnol. 90,
237–243 (2015)
8. F. Scherer, M. Anton, U. Schillinge, J. Henke, C. Bergemann, A. Kruger, B. Gansbacher, C.
Plank, Magnetofection: enhancing and targeting gene delivery by magnetic force in vitro and
in vivo. Gene Ther. 9, 102–109 (2002)
71
3.8 Conclusions
Spin-polarized metals have two channels of conductivity resulted in interesting applications including the most known giant magnetoresistance. Magnetic nanoparticles
have unusual features compared to bulk materials. They manifest superparamagnetic
properties in case of single-domain size. They have discrete density of states due to
quantum size effect. Our experiments with Co nanoparticles clearly show a new type
of plasmon excitation. This type of plasmon has unusual properties due to existence of
two independent groups of electrons with opposite spins providing weak interaction
so that all electron scattering processes occur without spin flip. Magnetic response of
the nanoparticles enables controlled and reversible aggregation accompanied by the
tailoring of optical absorption. Magnetic nature of the nanoparticles suggests a new
type of these plasmons. Magnetic response of Co nanoparticles shows less magnetic
moments per atom relative to the bulk value, namely 0.68 μ b and taking into account
the demagnetization factor 0.96 μ b per atom versus 1.7 μ b . The exchange interaction of electrons splits the energy bands between spin-up electrons and spin-down
electrons. It makes possible to coexist two independent channels of conductivity as
well as two independent plasmons in the same nanoparticle with very different electron relaxation. Indeed, the density of empty states in a partially populated d-band
is high, resulting in a large relaxation rate of the spin-down conduction electrons
and consequently in low quality of the plasmon resonance. In contrast, the majority
electrons with a completely filled d-band do not provide final states for the scattering
processes of the conduction spin-up electrons, therefore supporting a good quality
plasmon resonance. The scattering without spin flip is required to keep these two
plasmons independent.
References
1. P.B. Johnson, R.W. Christy, Optical constants of transition metals: Ti, V, Cr, Mn, Fe Co, Ni,
and Pd. Phys. Rev. 9, 5056 (1974). https://doi.org/10.1103/PhysRevB.9.5056
2. H. Bhata, A.E. Aliev, V.P. Drachev, New mechanism of plasmons specific for spin-polarized
nanoparticles. Sci. Rep. 9, 2019 (2019). https://doi.org/10.1038/s41598-019-38657-w
3. A.R. Young, Chromophores in human skin. Phys. Med. Biol. 42, 789–802 (1997)
4. G.J. Thomas, Raman spectroscopy of protein and nucleic acid assemblies. Annu. Rev. Biophys.
Biomol. Struct. 28, 1–27 (1999)
5. Y. Kumamoto, A. Taguchi, N.I. Smith, S. Kawata, Deep UV resonant Raman spectroscopy for
photodamage characterization in cells. Biomed. Optics Express 2, 927–936 (2011)
6. H. Takeuchi, UV Raman markers for structural analysis of aromatic side chains in proteins.
Anal. Sci. 27, 1077–1086 (2011)
7. L. Ashton, C.E.M. Hogwood, A.S. Tait, J. Kuligowski, C.M. Smales, D.G. Bracewell, A.J.
Dicksone, R. Goodacre, UV resonance Raman spectroscopy: a process analytical tool for host
cell DNA and RNA dynamics in mammalian cell lines. J. Chem. Technol. Biotechnol. 90,
237–243 (2015)
8. F. Scherer, M. Anton, U. Schillinge, J. Henke, C. Bergemann, A. Kruger, B. Gansbacher, C.
Plank, Magnetofection: enhancing and targeting gene delivery by magnetic force in vitro and
in vivo. Gene Ther. 9, 102–109 (2002)