Antonio García-Martín http://www.imm-cnm.csic.es/magnetoplasmonics Instituto de Microelectrónica de Madrid Consejo Superior de Investigaciones Científicas Magnetoplasmonics: fundamentals and applications 1
MAGNETO-PLASMONICS Control of MO activity with plasmon excitation P MO Control plasmon properties with an external magnetic field 2
The Lycurgus cup (British Museum. 4th Century) When illuminated from outside the cup appears green, but turns into red when illuminated from inside. PLASMONICS Active topic, but not so new Labors of the Months (Norwich, England, ca. 1480) The ruby color is probably due to embedded gold nanoparticles. 3
PLASMONICS based on Electromagnetic excitation (TM polarized) localized at the interface between a media r <0 (metal) and a media r >0 (dielectric material) Main characteristics Strong localization of EM in subwavelength volumes: Optical nanodevices Very sensitive to metal dielectric interface: Sensors 4
PLASMONICS that are excited if both frequency and wavevector match those of the SPP (propagating plasmon) c Ways to produce the extra k A prism A grating A defect Extra k the frequency matches that of the LSPP (localized plasmon) 5
MAGNETO-OPTICS New effect 1791-1867 Faraday effect: 1845 Bd Kerr effect: 1876 B 1824-1907 6
MAGNETO-OPTICS Kerr effect depends on relative orientation of B E ε k k E E ε k k z θ 0 θ 0 y M M M x Polar + i = f(m z ) Transverse R pp = f(m y ) Longitudinal + i = f(m x ) am am z 0 0 z 0 0 0 am 0 0 am 0 y y 0 0 0 0 am am x x 7
real mo imag MAGNETO-PLASMONICS Effects of magnetic field on optical properties of metals (Drude): x z y B Ag mo 0 0 mo 0 0 mo 2 2 2 p p i 2 2 2 2 ( ) 2 2 p c p c i 2 2 2 2 2 ( ) 30 20 10 0-300 1.0 0.5 r (Au) i (Au) r (Ag) i (Ag) c eb * m mo small for metals -600 Au, Ag 0.5 1.0 1.5 2.0 Energy (ev) 0.0 0.5 1.0 1.5 2.0 Energy (ev) ħω c = 0.115 mev (B=1 Tesla) 8
Reflectivity (%) mo M MAGNETO-PLASMONICS mo in noble metals is very small Solution: ferromagnetic metals 1.5 1.0 0.5 (Co) r (Co) i (Ag) r (Ag) 1 mo ( Co, Fe, Ni) M M ( B ~ 0.005 T ) mo sat ( Ag, Au) B -0.02 0.00 0.02 Magnetic field (Ts) 0.0 1.5 2.0 2.5 3.0 Energy(eV) 100 80 Ferromagnetic metals are very absorbent very broad plasmonic resonances 60 40 20 10 nm Co 50 nm Au 40 60 80 Incident angle 9
Kerr Rotation (deg) MAGNETO-PLASMONICS mo in noble metals is very small Solution: ferromagnetic metals Ferromagnetic nanowires Adv. Mat. 19, 2643 (2007) 0.1 0.0 Energy (ev) 4 3 2 Ni Bulk Wires Membrane -0.1 Ferromagnetic membranes Appl. Phys. Lett. 94, 062502(2009) 300 400 500 600 700 800 Wavelength (nm) No plasmon excitation Plasmon excitation 10
Reflectivity (%) MAGNETO-PLASMONICS Magnetoplasmonic materials: Hybrid ferromagnetic noble metal systems 100 80 60 40 20 22nm Au / 6 nm Co / 6nm Au 50 nm Au 40 60 80 Incident angle Fair plasmonic modes Good MO activity 11
Plasmon effects on the Kerr effect in nanostructured media Disordered Au/Co/Au nanosdiscs Small (2008) Au discs over Au/Co/Au film Opt. Express (2008) 12
Fabrication of Au/Co/Au dots Fabrication method: Sputtering+ colloidal lithography Au/Co/Au layer Polyelectrolyte - - - - - - - Latex spheres + + + + + + + Ar J.B. González et.al. Small 4,202 (2008) 13
Absorption (a.u.) Optical and magneto-optical analysis 2.0 1.5 60 Au/Co/Au 110 Au/Co/Au 85nm 1.0 0.5 1.6 2.0 2.4 2.8 3.2 Energy (ev) Peak in the LSPR spectral region Shifts to lower energy as D/H increases 85nm J.B. González et.al. Small 4,202 (2008) 14
( 2 + ) NP /(f*( 2 + ) CF ) Optical and magneto-optical analysis 5 4 3 2 1 60 110 1.5 2.0 2.5 3.0 Energy (ev) A large enhancement of the MO activity of the system is observed in the region corresponding to the excitation of the localized surface plasmon. J.B. González et.al. Small 4,202 (2008) 15
Dots over Au/Co/Au Square periodic array Au nanodiscs (Grating) (e-beam Φ:110nm,h 20nm,a:250-400nm) SiO 2 (e-beam ev.) variable thickness Au:6 Co:10 Au:16 Localized SP SPP Excited by periodic array Plasmon excitation: Glass k k G sp // light -Disc diameter: tunes LSP energetic position -Array periodicity (grating): tunes G vector and allows exciting SPP -Spacer thickness: tunes LSP vs SPP overlapping/interaction G. Armelles et. al. Opt. Express 16, 16104 (2008) 16
Rotation ( ) Ellipticity( ) Dots over Au/Co/Au 0.1 0.0 d = 300 nm t SiO2 = 50 nm -0.1-0.2-0.3-0.4 The magneto-optical activity of the system is strongly modified in the region corresponding to the localized surface plasmon of the gold disc. -0.5 1.50 1.75 2.00 2.25 2.50 2.75 3.00 Energy (ev) G. Armelles et. al. Opt. Express 16, 16104 (2008) 17
r ps discs /rps no discs r pp discs /rpp no discs discs / no disc Dots over Au/Co/Au 1.2 1.0 0.8 The purely optical component, r pp, contributes to the magnetooptical activity enhancement due to the dip at the LSP position Optical contribution 0.8 0.6 0.4 0.2 The purely magnetooptical contribution, r ps, is modified around the LSP position k i k r r ps pp 1.50 1.75 2.00 2.25 2.50 2.75 3.00 Energy (ev) MO contribution 1.2 0.8 0.4 G. Armelles et. al. Opt. Express 16, 16104 (2008) 18
r ps discs /rps no discs r pp discs /rpp no discs H (a.u.) H (a.u.) discs / no discs Dots over Au/Co/Au 4 2 0 Energy = 1.62eV Without Disks With Disks Au Co Au 70 80 90 100 x (nm) 4 2 0 Energy = 1.82eV Without Disks With Disks Au Co Au 70 80 90 100 x (nm) The purely magnetooptical contribution, r ps, is related to the redistribution of the electromagnetic field inside the Co layer E discs /E no discs 1.2 1.0 0.8 0.6 0.4 1.50 1.75 2.00 2.25 2.50 2.75 3.00 Optical contribution 1.5 2.0 2.5 3.0 Energy (ev) 1.50 1.75 2.00 2.25 2.50 2.75 3.00 Energy (ev) MO contribution 1.4 1.2 1.0 0.8 0.8 0.6 0.4 0.2 1.2 0.8 0.4 G. Armelles et. al. Opt. Express 16, 16104 (2008) 19
Reflectance Reflectance Application as a sensor Operation Principle of Surface Plasmon Resonance sensor Liquid ( l ) m l ksp k0 Resonant angle shift due to a l m Au layer ( m ) Glass Prism change in the refractive index 1,0 0,9 0,8 0,7 0,6 0,5 0,4 n 1 <n 2 0,3 0,2 0,1 1 2 0,0 55 60 65 70 75 80 85 90 Angle of incidence (deg) Real time monitoring of the refractive index change at a fixed angle 0,55 0,50 0,45 0,40 0,35 0,30 n 1 0,25 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 Time (min) n 2 Sensor Device : External Medium d Receptor Analyte SP k x Evanescent Field detects changes in the local refractive index m Metallic layer k xp 2 P sin Evanescent Field ~ 80 nm (45 nm Au, = 632 nm) 20
M (a.u.) R(M)/R(0) R( )/R(0) Reflectance Reflectance MOSPR: Angular derivative Au Au/F/Au Resonant angle depends on magnetization (M) k k k light // sp 0 sp k x (1 ) sp M k0 sp z x 1,0 0,5 0,0-0,5-1,0 y Magnetization switching angular derivative Rpp R ( M ) R ( M ) (0) -0,01 0,00 0,01 Magnetic Field (Teslas) B sin(ωt) pp 1.0 0.5 0.0 pp 40 45 Theta (deg) M x -M x inc 0.004 M z -M z 0.002 0.000 10 5 0-5 -10 43.8 44.0 44.2 TMOKE OPT DER Theta (deg) Fe 5nm 66 68 70 72 74 Theta (deg) J.B. González-Diaz et.al. Phys. Rev B76, (2007) 21
R(%) R(M)/R MOSPR vs. SPR Sharper angular curves (Angular derivative) Higher sensitivity n Emin 100 80 60 40 20 30 nm Au / 5 nm Fe / 5 nm Au 48 nm Au 55 60 65 70 75 Theta (deg) 0.01 0.00-0.01 S / S Emin 350 300 250 200 150 100 50 0 MOSPR SPR MOSPR SPR 5 10-6 1.5 10-5 TMOKE/noise R/noise -50 0.000 0.001 0.002 B. Sepulveda et al., Optics Letters 31 (2006) 1085 + Patent. n d 22
Conclusions Using materials exhibiting plasmonic and magneto optical activity simultaneously we have shown: Enhancement of MO activity due to SPP-Light coupling Magnetic field modifies the SPP momentum Applications Sensing Novel scheme exploiting: a) Electromagnetic field localization b) External modulation via magnetic field Optronics Communications: external control Photonics on silicon:potential structure for dynamic behaviour of plasmonic components Data storage: MO plasmon-mediated enhancement Enhanced magneto-optical media & patterned MO media 23
Acknowledgments A.Garcia-Martin J.Fernandez M.U.Gonzalez G.Armelles A.Cebollada Scientific staff J.M. Garcia-Martin J.B.Gonzalez E.Ferreiro R.Fermento PhD Students Post docs A.Vitrey Staff (Collaboration) J.V.Anguita Technician D.Meneses D.Martin A. Calle P.Prieto http://www.imm-cnm.csic.es/magnetoplasmonics 24
Acknowledgments U. Chalmers University of Toledo ICFO ICMM CIN2 University of Michigan 25
Acknowledgments EU Regional (CAM) www.nanomagma.org Nanomagnet National (MICINN,CSIC) Crimafot Bioptomag Funcoat Magplas 26
Magnetoplasmonics: fundamentals and applications http://www.imm-cnm.csic.es/magnetoplasmonics Instituto de Microelectrónica de Madrid Consejo Superior de Investigaciones Científicas 27