Magnetization-induced optical second- and third-harmonic generation in magnetic nanostructures

Transcription

1 Laboratory of Nonlinear Optics of Nanostructures & Photonic Crystals Moscow State University Magnetization-induced optical second- and third-harmonic generation in magnetic nanostructures.shg.ru Т.V. Мurzina Department of Physics, Мoscow State University, Moscow, Russia

2 Collaborators.M. Kim, R.V. Kapra, O.A. Aktsipetrov, Department of Physics, Мoscow State University, Moscow, Russia A.F. Kravets, A.Ya. Vovk, Institute of Magnetizm NAS of Ukraine, Kiev, Ukraine V.G. Golubev, D.A. Kurdyukov, S.F. Kaplan Ioffe Physico-Technical Institute, St. Petersburg, Russia M. Inoue, H. Uchida, Toyohashi University of Technology, Toyohashi, Japan

3 Outline Nonlinear magneto-optics in magnetic materials - MSHG and MTHG, historical aspect; - phenomenological description, nonlinear magnetooptical Kerr effect NOMOK; xperimental studies of magnetization induced secondand third-harmonic generation in: - magnetic nanolayers; - magnetoresistive nanogranular films; - magnetophotonic microcavities, - YIG-substituted artificial opals and PS-based 1D photonic crystals Conclusions

4 Nonlinear magneto-optics Magneto-Optics magneto-optical Faraday 1845 and Kerr 1887 effects Nonlinear Optics Bloembergen Nonlinear Magneto-Optics A.K. Zvezdin prediction O.A. Aktsipetrov observation MSHG as a fundamental optical effect: polarization and intensity effects Hyper-Rayleigh scattering Reflects magnetic properties of a media Sensitive to surface and interface magnetization J. Shimura, S. Ohkoshi, K. Hashimoto, APL, 3 - MTHG in Bi-, Al-doped YIG O.A. Aktsipetrov et.al., JTP Letters, 3 - MTHG in magneto-photonic microcavities

5 Scope of the talk Magnetic nanostructures Magnetizationinduced second harmonic generation - Magnetic nanogranular films Co-Ag, CoFe-Al O 3 Nanostructured photonic crystals - Magnetophotonic crystals - Bi:YIG substituted artificial opals - Bi:YIG substituted porous silicon bazed photonic crystals Magnetization-induced thrid harmonic generation Magnetic nanolayers Co, Fe

6 Magnetic nanostructures -? Surface localization of Centrosymmetric media Bulk localization of 3 3 bulk surface nanoparticles 3 bulk Thin metal films

7 Linear and nonlinear magneto-optical response Linear magneto-optical processes: wave equation Gyrotropic effects: 1 ε ω ω + c t ε iεq ˆ ε = iεq ε, ε Q M 1 ω = ω Harmonics generation NL L 3 P = P L + 3 P = P + P + P P

8 Nonlinear magneto-optical effects 1 ω ε ω ω ε ω t c t c P = + Nonlinear wave equation - inhomogeneous tan ω ω ω ω ε φ ψ i i K K K = + = Nonlinear-optical magnetic Kerr effect: Magnetic birefringence decomposition of into left- and righthanded circularly polarized light ω k x z M longitudinal Kerr effect k M x z transversal Kerr effect

9 Comparison of electro-induced and magneto-induced effects Polar vector Axial vector r static H r static Magnetic field doesn t break inversion symmetry -tensor pseudo-tensor Structure of Tensors are different

10 Nonlinear-optical responce of a magnetic media: SHG Nonlinear polarization P 1 ˆ = α :ω + ˆ :ωω +... М : Non-zero elements of the susceptibility tensor are governed by the symmetry operations, Т ˆ D ik =T T T ˆ ii' D Surface ' ; kk' Centrosymmetric media ˆ i' ' k' D Bulk, = Magnetized media- additional symmetry operations ik M = ± T ˆ r ii' M = ˆ r M = T ' T kk' ± ˆ v ± i' ' k ' ± M ± M M, Magneto-induced variations of SHG intensity High sensitivity to surfaces and interfaces of centrosymmetric media I = M ± ± M = M cosϕ + M

11 I P = Magnetization-induced SHG and THG M 1 3 ˆ α : + ˆ : + ˆ = ω ω ω :ωωω Мagnetization-induced effects ± ± M = M cosϕ + M +... ρ Magnetization-induced intensity changes: SHG magnetic contrast = I I M M I + I M M Transversal magneto-optical Kerr effect ϕ + Total Magnetization-induced rotation of polarization plane φ K Re s, p / p, p Longitudinal magneto-optical Kerr effect Total Magnetic properties of the bulk of a media

12 Magnetization-induced SHG and THG: symmetry considerations Combination Of polarizations Centrosymmetric media M OX M OY xxx, xzz, p-in, p-out zzz, zxx, xxz zzx p-in, s-out yxx, yzz s-in, p-out zyy xyy s-in, s-out yyy Intensity changes: magnetic contrast Transversal Kerr effect Н Н Polarisation changes Combination of polarizations M OX M OY p-in, p-out zzzz, xxxx, xzzz, zxxx, xxzz, zxzx xxxz, zxzz p-in, s-out yxxz, yzzz s-in, p-out zyyy s-in, s-out yyyy

13 xperimental set-up and samples SHG/THG interferometry OPO, nm The pulse width - 15ns repetition rate - 5 Hz intensity - 1 MV/cm =164 nm YAG-Nd 3+ polarizer PMT BG BG sample UG M Reference SHG/THG source L Ref Sample M Samp Ref Samp I L= + - magnetization-induced changes in the intensity and phase of the SHG/THG Magnetic field of koe Transversal Kerr effect I + L, M I I ref I s ref ± I s M + πl M cos + Φ T s M Φ ref

14 ρ SHG intensity, arb. un. 3,5 3,,5, 1,5 1,,5 Thin metal films: MSHG and MTHG interferometry Co film 1 nm thick 3, I M + I M,, = I M + + I M 3, cryst, 15 / ω M- M Translator position, cm. cos ϕ THG intensity, arb. un. 3 1 Φ M+ ϕ Phase shift = 7 M M M Position of the translator, cm ρ.3 ρ3 ω =.8 ±. / ω.55

15 ρ MSHG and MTHG interferometry 3, I M + I M,, = I M + + I M 3, cryst, Fe11 film 1 nm thick cos ϕ S H G in te n s ity, a rb. u n Position of the translator, cm THG intensity, arb. un. 3 1 M- 1 M Position of the translator, cm ρ ω.45 ρ3 ω =.8 ±..3.1 ±. 3

16 Nanogranular magnetic films - nanogranular magnetic films Co x Ag 1-x,Co x AlO 1-x granular size 3-5 nm Composition Magnetoresistance, % Magnetic field, koe 4 cm Co 49 cm cm Ag Мagnetoresistance R R H ρ MR = R Granular films of the composition 6 < x < 8 vol.% and of 4 nm thick are deposited on glass ceramic substrates at the residual pressure 1-4 Pa using dual electron beam deposition system A.F. Kravets, A.Ya. Vovk, Institute of Magnetizm NAS of Ukraine, Kiev, Ukraine

17 Symmetry of nanogranular films: anisotropic measurements SHG intensity arb.un. THG intensity arb.un Co x Ag 1-x Co 9 x Al O 3 1-x pp geometry ps geometry pp geometry SH Intensity arb.un TH Intensity arb.un sp geometry pp geometry ps geometry ps geometry 33

18 Magnetization-induced SHG and THG in Co x Ag 1-x films ρ..1 cryst M , Magnetoresistance, % ,15,1,5 THG magnetic contrast ρ M cryst ffects are of the same order! - Correlation between GMR and NOMOK - the key role of interfaces,1,,3,4,5,6,7,8 Concentration of Со in Co x Ag 1-x films ρ =.7 cryst M.5

19 Magnetization-induced SHG and THG in Co x Al O 3 1-x films ρ 3, I M + I M,, = I M + + I M 3, cryst, cos ϕ THGSHG magnetic contrast,15,1,5,15,,5,3,35,4 Content of Co in CoAl O 3 films 4 Magnetoresistance % THG intensity, arb. un M - M + phase shift Position of reference, cm.6

20 Magnetophotonic crystals and microcavities Photonic crystals: k r = k r + G r ω nhancement ω P M,,1 M of local optical fields at the M PBG edge = = + : ω +... ω Fulfillment of phase matching conditions at the PBG edge Microcavities: Resonant enhancement of local optical fields at microcavity modes Obectives: design and fabrication of magnetophotonic crystals; realization of phase-matched magnetization-induced SHG in photonic crystals ; search for the enhancement of the nonlinear magneto-optical effects

21 1D magnetophotonic microcavities based on Bi :YIG FSM image n SiO /Ta O i d i =λ /4 5 DBR { SiO /Ta O 5 { Bi:YIG DBR n i d i =λ /4 Fabrication: bottom DBR sputtering Bi:YIG layer sputtering glass substrate by rf sputtering in an Ar+ atmosphere, sputtering pressure of 6 mtorr; Annealing in air at 7 C for min top DBR sputtering { { { { Toyohashi University of Technology, Toyohashi, Japan

22 1D magnetophotonic microcavities based on Bi substituted YIG Transmission Coefficient Faraday Rotation deg 9 /mm at 11 nm enhancement by factor of Wavelength nm

23 Magnetization-induced effects in SHG and THG intensity in 1D magnetophotonic microcavity SHG and THG k-spectra for the opposite directions of magnetic field, transversal nonlinear magneto-optical Kerr effect k p-in, p-out THG z M x 5 3,5 SHG intensity, arb. un ,,75,5,5 SHG magnetic contrast MTHG intensity, arb. un. 3,,5, 1,5 1,,5 M+ M-,3,,1 THG magnetic contrast, Angle of incidence, deg., Angle of incidence, deg., ρ 3, I M + I M,, = I M + + I M 3, cryst, cos ϕ

24 Longitudinal magnetization: rotation of the polarization plane in 1D magnetophotonic microcavity SHG intensity, arb. un Analyzer azimuthal angle, deg Combination Of polarizations longitudinal Kerr effect k z M,, M OX M OY p-in, p-out zzz, zxx, xxz xxx xzz zzx p-in, s-out yxx, yzz s-in, p-out zyy xyy s-in, s-out yyy x Polarisation changes

25 Reflectivity, arb. un D - opals Yttrium iron-garnet infiltrated opals: magnetic 3D photonic crystals Wavelength, nm ,4,5,6 -SiO sphere diameter 4 nm,7 -Opals+Pt5%vol - Soaking by the colloidal solution of Bi:YIG - Annealing T=13 K Bi:YIG filling factor 5-3% vol.,8 V.G. Golubev, D.A. Kurdyukov, S.F. Kaplan Ioffe Physico-Technical Institute, St. Petersburg, Russia

26 1 3 4 Fundamental wavelength nm ρ = 7.5%,,5,1,15,4,5 Fundamental wavelength nm Yttrium iron-garnet infiltrated opals: magnetic 3D photonic crystals Transversal Kerr effect Н SHG magnetic contrast [%] SHG Intensity arb.un. Reflectivity ρ ω = I M + I M I M + + I M

27 Photonic crystals based on porous silicon 5 porous layers Side view of cross-section of periodic porous structure 5 porous layers n-type Si1 wafer of. Ωcm; the alternate layers are etched at current densities of 1mA/cm and 5mA/cm Top view of random lateral pore distribution

28 Magnetophotonic crystals based on porous silicon PBG as a function of angle of incidence Transversal Kerr effect Н SHG Intensity arb.un ρ +M - M I M + I = I M + + I M M,5,4,3,,1 Magnetic contrast SHG as a function of angle of incidence Fundamental wavelength nm

29 Conclusions Magnetization-induced optical second- and third-harmonics generation are demonstrated to be a sensitive probe of magnetic nanostructures Magnetization-induced optical third-harmonic generation is observed experimentally in a number nanostructures. The values of magnetization-induced effects in THG in nanostructures are of the same order of magnitude as for the case of SHG.

30 Thank you!