Magneto-Optical Effect and Applications

Transcription

1 Magneto-Optical Effect and Applications Takao Suzuki 1

2 Contents 1.Background 2.Basic Physics 3.Applications 4. Nano-MOKE 2

3 Background Michael Faraday ( ) Ref.: J.F. Keithley Electrical and Magnetic Measurements- 500BC to the 1940s (IEEE Press, New York) John Kerr ( ) 3

4 Linear Polarization Wikipedia 4

5 Circular Polarization Wikipedia 5

6 Elliptical Polarization Wikipedia 6

7 RCP and LCP RCP and LCP Δɸ ΔA ΔA and Δɸ Linear Polarization RCP + LCR Optical Rotary Power Δɸ Circular Dichoism Δn = n RCP - n LCR Ref: K. Satoh: Optics and Magnetism (Asakura Shoten, 1983), p.25. (in Japanese) 7

8 Faraday Effect θ F v: Verdet constant θ F = ω(δn)d/2c (Δn = n + - n - ) Wikipedia 8

9 Discovery of Rotation in Polarization θ F This discovery was made in 1811, much earlier than Faraday s finding (1845), and Kerr s one (1876)!! Francois Arago ( ) 25 th Prime Minister of France (5/1848-6/1848) Wikipedia 9

10 Cotton - Effect (1895) θ F Aimé Auguste Cotton ( ) Known for Cotton Mouton effect Wikipedia 10

11 Cotton Mouton Effect (1907) θ F H Aimé Auguste Cotton ( ) Ref.: J.F. Keithley Electrical and Magnetic Measurements- 500BC to the 1940s (IEEE, New York) Application: Optical isolator Henry Mouton ( ) No photograph available 11

12 Circular Polarization of Light Jean-Baptiste Biot ( ) Known for Bio - Savart Law Augustin-Jean Fresnel ( ) Known for wave optics Aimé Auguste Cotton ( ) Known for Cotton Mouton effect Ref.: J.F. Keithley Electrical and Magnetic Measurements- 500BC to the 1940s (IEEE, New York) 12

13 If denotes the penetration depth, we have Kerr Effect (Signal proportional to Rθ k which is also to RM) (Signal proportional to Rθ k which is also to RM ) Cotton- Mouton Effect (Birefringence effect) (Signal proportional to M 2 ) Wikipedia 13

14 Domain Observations Kerr Observation of Domains of FeSi Kerr Observation of Domains of NdFeB Faraday Observation of Domains of (YBi) 3 Fe 5 O 12 14

15 Switching the Magnetic Vortex Core by a Single Period Field Burst Vortex core down B 0 = 1.5 mt Vortex core up B 0 = 0.4 mt toggling the vortex core orientation with short bursts of an alternating magnetic field f = 250 MHz B. Van Waeyenberge, A. Puzic, H Stoll, K.W. Chou et al. Nature 444, 461 (2006)

16 Ultra-fast Switching 22nm thick Ni thin film E. Beaurepaire et al., P.R.L., 76,

17 Contents 1.Background 2.Basic Physics 3.Applications 4. Nano-MOKE 17

18 Basis-Macroscopic According to classical physics, the speed of light varies with the permittivity of a material: where is the velocity of light through the material, is the material permittivity, and is the material permeability. Because the permittivity is anisotropic, polarized light of different orientations will travel at different speeds. 18

19 Basis Where D, E and g are Displacement Vector, Electric Field and Gyration Vector, respectively. Depends on M! 19

20 Basis Where D, E and g are Displacement Vector, Electric Field and Gyration Vector, respectively. Depends on M! 20

21 Basis When one considers a ferromagnetic substance with M along the z-axis, then one obtains, M M (2n+1) Terms Faraday and Kerr Effect M 2n Terms Cotton Mouton Effect: Δ ε= ε 1 ε 2 21

22 Further references The Physical Principles of Magneto-optical Recording by Masud Mansuripur (Cambridge University of Press,1995). 22

23 Basis-Microscopic Excited state Ground state Spin-orbit interaction High MO-Effect Materials: Large Spin-Orbit Splitting Δ Large Oscillation intensity f Appropriate Photon Energy ω 23

24 X-ray magnetic circular dichroism (XMCD) There is another example; Electron magnetic circular dichroism (EMCD).(EELS) 24

25 M-O Effect Strongly dependent on photon energy or wavelength High MO-Effect Materials: Large Spin-Orbit Splitting Δ Large Oscillation intensity f Appropriate Photon Energy ω Strong Spin-Orbit Coupling for Bi, 2.5ev (6p) Bi-YIG, Co-YIG, CdCr 2 Se 4, CoS 2, Cr 3 Te 4, MnBi, CeSb, EuS, FePt, etc 25

26 Enhancement of MO Effect by Pt TbFeCo Pt TbFeCo Pt Y.Itoh and T.Suzuki,IEEE TransMag.35, (1999). 26

27 MO Enhancement with Ordering in L1 0 FePt S H.Kanazawa, T.Suzuki: J.Magn.Soc.Japan 25,295 (2001). 27

28 Kerr Rotation for Various Materials fcc Co(100) fcc Co(111) TbFeCo Co 75 Pt 25 Co 50 Pt 50 (S=0.7) Fe 50 Pt 50 (S=0.8) TbFeCo (M-O 材料 ) θ k ( ) -0.4 L1o FePt photon energy(ev) High Kerr Effect at High Energy Range>High SNR T.Suzuki et al

29 ( 株 ) トヨタ マックスと共同開発製品 ( 販売実績あり!) Wide Wavelength Kerr Spectroscopic Apparatus (1.4 ~ 6.7 ev, 180 ~ 860 nm, 20 koe) (Technical Award by the Magnetics Society of Japan, 1999) T.Suzuki et al 29

30 Switching by Photon A. Kirilyuk, A. Kimel, T.Raising: Rev.Mod.Phys. 82,

31 Ultra-fast Switching A. Kirilyuk, A. Kimel, T.Raising: B. Rev.Mod.Phys. 82,

32 Polarization and Spin = + Linear Polarization Left Circular Polarization Right Circular Polarization Spin Up + Spin Down 32

33 Stern and Gerlach (1921) Ag ( single outer Electron!) 4d 10 5s 33

34 Participants at the 1930 Solvay Congress, which was devoted to magnetism. 34

35 Contents 1.Background 2.Basic Physics 3.Applications 4. Nano-MOKE 35

36 M Magnetic Bubble Memory s (YBi) 3 Fe 5 O 12 Bobeck et al: 13th Annual Conference on Magnetism and Magnetic Materials, Boston, Massachusetts, September 15,

37 Magneto-optical Recording s Wikipedia 37

38 Kerr Signal S = R (θ k2 + η k2 ) 1/2 N = R S/N = R (θ k2 + η k2 ) 1/2 38

39 Applications -Magneto-optical Recording- Amorphous TbFeCo Thin films <M> = M TM - M RE TM(Fe,Co,..) RE(Tb, Dy,..) 39

40 Applications -Magneto-optical Recording- 40

41 Magneto-optical Recording Magnetic Field Modulation 41

42 -Magneto-optical Recording- 42

43 -Magneto-optical Recording- 43

44 Further References Author: Richard J. Gambino, Takao Suzuki ISBN-13: Year: 1999 Publisher: Wiley-IEEE Press 44

45 Contents 1.Background 2.Basic Physics 3.Applications 4. Nano-MOKE 45

46 Nano-MOKE

47 Specs for Nano-MOKE Solid State Laser Diode (660 nm) Smallest detectable changes: 0.02% (Reflectivity), 0.5 mdeg (Polarization) 2 μm laser spot achievable, 5 μm typical Galvanometric mirrors for rastering Longitudinal and polar measurements Fields up to 0.12 T (quadpole), 0.46 T (dipole)

48 Domains in Permalloy Oe Oe Oe Oe Oe Oe

49 49