Magnetoplasmonics: fundamentals and applications

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Antonio García-Martín http://www.imm-cnm.csic.

1 Antonio García-Martín Instituto de Microelectrónica de Madrid Consejo Superior de Investigaciones Científicas Magnetoplasmonics: fundamentals and applications 1

2 MAGNETO-PLASMONICS Control of MO activity with plasmon excitation P MO Control plasmon properties with an external magnetic field 2

3 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

4 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

5 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

6 MAGNETO-OPTICS New effect Faraday effect: 1845 Bd Kerr effect: 1876 B

7 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 am 0 0 am 0 y y 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 ( )

8 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 p p i ( ) 2 2 p c p c i ( ) r (Au) i (Au) r (Ag) i (Ag) c eb * m mo small for metals -600 Au, Ag Energy (ev) Energy (ev) ħω c = 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.

9 Reflectivity (%) mo M MAGNETO-PLASMONICS mo in noble metals is very small Solution: ferromagnetic metals (Co) r (Co) i (Ag) r (Ag) 1 mo ( Co, Fe, Ni) M M ( B ~ T ) mo sat ( Ag, Au) B Magnetic field (Ts) Energy(eV) Ferromagnetic metals are very absorbent very broad plasmonic resonances nm Co 50 nm Au Incident angle 9

10 Kerr Rotation (deg) MAGNETO-PLASMONICS mo in noble metals is very small Solution: ferromagnetic metals Ferromagnetic nanowires Adv. Mat. 19, 2643 (2007) Energy (ev) Ni Bulk Wires Membrane -0.1 Ferromagnetic membranes Appl. Phys. Lett. 94, (2009) Wavelength (nm) No plasmon excitation Plasmon excitation 10

11 Reflectivity (%) MAGNETO-PLASMONICS Magnetoplasmonic materials: Hybrid ferromagnetic noble metal systems nm Au / 6 nm Co / 6nm Au 50 nm Au Incident angle Fair plasmonic modes Good MO activity 11

12 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

13 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.

2 Energy (ev) Peak in the LSPR spectral region Shifts to lower

14 Absorption (a.u.) Optical and magneto-optical analysis Au/Co/Au 110 Au/Co/Au 85nm 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

15 ( 2 + ) NP /(f*( 2 + ) CF ) Optical and magneto-optical analysis 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.

// light -Disc diameter: tunes LSP energetic position -Array periodicity (grating): tunes G vector and allows

16 Dots over Au/Co/Au Square periodic array Au nanodiscs (Grating) (e-beam Φ:110nm,h 20nm,a: nm) 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, (2008) 16

17 Rotation ( ) Ellipticity( ) Dots over Au/Co/Au d = 300 nm t SiO2 = 50 nm The magneto-optical activity of the system is strongly modified in the region corresponding to the localized surface plasmon of the gold disc Energy (ev) G. Armelles et. al. Opt. Express 16, (2008) 17

18 r ps discs /rps no discs r pp discs /rpp no discs discs / no disc Dots over Au/Co/Au The purely optical component, r pp, contributes to the magnetooptical activity enhancement due to the dip at the LSP position Optical contribution The purely magnetooptical contribution, r ps, is modified around the LSP position k i k r r ps pp Energy (ev) MO contribution G. Armelles et. al. Opt. Express 16, (2008) 18

19 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 Energy = 1.62eV Without Disks With Disks Au Co Au x (nm) Energy = 1.82eV Without Disks With Disks Au Co Au 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 Optical contribution Energy (ev) Energy (ev) MO contribution G. Armelles et. al. Opt. Express 16, (2008) 19

20 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, , 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

21 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 pp Theta (deg) M x -M x inc M z -M z TMOKE OPT DER Theta (deg) Fe 5nm Theta (deg) J.B. González-Diaz et.al. Phys. Rev B76, (2007) 21

22 R(%) R(M)/R MOSPR vs. SPR Sharper angular curves (Angular derivative) Higher sensitivity n Emin nm Au / 5 nm Fe / 5 nm Au 48 nm Au Theta (deg) S / S Emin MOSPR SPR MOSPR SPR TMOKE/noise R/noise B. Sepulveda et al., Optics Letters 31 (2006) Patent. n d 22

23 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

24 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 24

25 Acknowledgments U. Chalmers University of Toledo ICFO ICMM CIN2 University of Michigan 25

26 Acknowledgments EU Regional (CAM) Nanomagnet National (MICINN,CSIC) Crimafot Bioptomag Funcoat Magplas 26

27 Magnetoplasmonics: fundamentals and applications Instituto de Microelectrónica de Madrid Consejo Superior de Investigaciones Científicas 27

Optimizing light harvesting for high magnetooptical performance in metal-dielectric magnetoplasmonic nanodiscs

Optimizing light harvesting for high magnetooptical performance in metal-dielectric magnetoplasmonic nanodiscs Alfonso Cebollada, Juan Carlos Banthí, David Meneses, Fernando García, María Ujué González,