Magneto-Optical Effect and Applications

THE UNIVERSITY OF ALABAMA MINT

Center for Materials for INformation Technology

Takao Suzuki

Magneto-Optical Effect and Applications

1June 27, 2014



Contents

2June 27, 2014

1.Background

2.Basic Physics

3.Applications

4.MINT Nano-MOKE



Background

Michael Faraday(1791 – 1867)

John Kerr(1824 – 1907)

3June 27, 2014

Ref.: J.F. Keithley “Electrical and Magnetic Measurements-500BC to the 1940s” (IEEE Press, New York)



Linear Polarization

4June 27, 2014

Wikipedia



Circular Polarization

5June 27, 2014

Wikipedia



Elliptical Polarization

6June 27, 2014

Wikipedia



RCP and LCP

7June 27, 2014

RCP and LCP Δɸ ΔA ΔA and Δɸ

• Linear Polarization RCP + LCR• Optical Rotary Power Δɸ • Circular Dichoism Δn = nRCP - nLCR

Ref: K. Satoh: Optics and Magnetism (Asakura Shoten, 1983), p.25. (in Japanese)



Faraday Effect

8June 27, 2014

θF= ω(Δn)d/2c (Δn = n+ - n-)

θF

Wikipedia

v : Verdet constant



Discovery of Rotation in Polarization

9June 27, 2014

Francois Arago(1786 – 1853)

25th Prime Minister of France(5/1848-6/1848)

θF

Wikipedia

This discovery was made in 1811, much earlier than Faraday’s finding (1845), and Kerr’s one (1876) !!



Cotton - Effect (1895)

10June 27, 2014

Aimé Auguste Cotton(1869 – 1951)

Known for Cotton – Mouton effect

θF

Wikipedia



Cotton – Mouton Effect (1907)

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H

Henry Mouton ( 1869 - 1935 )

No photograph available

Application: Optical isolator

θF

Ref.: J.F. Keithley “Electrical and Magnetic Measurements-500BC to the 1940s” (IEEE, New York)



Circular Polarization of Light

12June 27, 2014

Jean-Baptiste Biot(1774 -1862)

Known for Bio - Savart Law

Augustin-Jean Fresnel(1788 – 1827)

Known for wave optics


Known for Cotton – Mouton effect

Ref.: J.F. Keithley “Electrical and Magnetic Measurements-500BC to the 1940s” (IEEE, New York)



Kerr Effect

13June 27, 2014

If denotes the penetration depth, we have

Cotton- Mouton Effect (Birefringence effect) (Signal proportional to M2)

(Signal proportional toRθk which is also to RM⁄⁄)

(Signal proportional toRθk which is also to RM)

Wikipedia

Kerr Observation of Domains of NdFeB

Faraday Observation of Domains of (YBi)3Fe5O12

Domain Observations

Kerr Observation of Domains of FeSi

June 27, 2014 14

Vortex core down Vortex core up

toggling the vortex core orientation with short bursts of an alternating magnetic field

B0= 1.5 mT

B0= 0.4 mT

f = 250 MHz

Switching the Magnetic Vortex Core by a Single Period Field Burst

B. Van Waeyenberge, A. Puzic, H Stoll, K.W. Chou et al. Nature 444, 461 (2006)



Ultra-fast Switching

16June 27, 2014

22nm thick Ni thin film

E. Beaurepaire et al., P.R.L., 76, 1996.



Contents

17June 27, 2014

1.Background

2.Basic Physics

3.Applications

4.MINT Nano-MOKE



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.

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Basis

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Where D, E and g are Displacement Vector, Electric Field and Gyration Vector, respectively.

Depends on M !



Basis

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Where D, E and g are Displacement Vector, Electric Field and Gyration Vector, respectively.

Depends on M !



Basis

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M

M2n TermsM(2n+1) Terms

Cotton – Mouton Effect: Δ ε= ε1 – ε2Faraday and Kerr Effect

When one considers a ferromagnetic substance with M along the z-axis, then one obtains,



Further references

22June 27, 2014

“The Physical Principles of Magneto-optical Recording” by Masud Mansuripur (Cambridge University of Press,1995).



Basis-Microscopic

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Excited state

Ground state

Spin-orbit interaction

High MO-Effect Materials:• Large Spin-Orbit

Splitting Δ• Large Oscillation

intensity f• Appropriate Photon

Energy ω



X-ray magnetic circular dichroism(XMCD)

24June 27, 2014There is another example； Electron magnetic circular dichroism (EMCD).（EELS)



M-O Effect

25June 27, 2014

Strongly dependent on photon energy or wavelength

High MO-Effect Materials:• Large Spin-Orbit Splitting Δ• Large Oscillation intensity f• Appropriate Photon Energy ω

Bi-YIG, Co-YIG, CdCr2Se4, CoS2, Cr3Te4, MnBi, CeSb, EuS, FePt, etc…

Strong Spin-Orbit Coupling for Bi , 2.5ev (6p)



Enhancement of MO Effect by Pt

26June 27, 2014

Y.Itoh and T.Suzuki,IEEETransMag.35, (1999).

Pt

Pt

TbFeCo

TbFeCo



MO Enhancement with Ordering in L10 FePt

27June 27, 2014

H.Kanazawa, T.Suzuki: J.Magn.Soc.Japan 25,295 (2001).

S

28

1 2 3 4 5 6 7-1.2

-0.8

-0.4

0.0

0.4

0.8

θ

k(°

)

photon energy(eV)

Co75Pt25

Fe50Pt50(S=0.8)

TbFeCofcc Co(111)fcc Co(100)

Co50Pt50(S=0.7)

Kerr Rotation for Various Materials

High Kerr Effect at High Energy Range＞High SNR

L1o FePt

TbFeCo (M-O 材料）

T.Suzuki et al. 2000June 27, 2014

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Wide Wavelength Kerr Spectroscopic Apparatus(1.4 ~ 6.7 eV, 180 ~ 860 nm, 20 kOe)

（Technical Award by the Magnetics Society of Japan , 1999）

（株）トヨタ・マックスと共同開発製品（販売実績あり！）

T.Suzuki et al June 27, 2014



Switching by Photon

30June 27, 2014

A. Kirilyuk, A. Kimel, T.Raising: Rev.Mod.Phys. 82, 2010.



Ultra-fast Switching

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A. Kirilyuk, A. Kimel, T.Raising:B. Rev.Mod.Phys. 82, 2010.



Polarization and Spin

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+=

Linear Polarization Left Circular Polarization Right Circular Polarization

Spin Up + Spin Down

Stern and Gerlach (1921) Ag ( single outerElectron!)

4d105s

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June 27, 2014 34

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



Contents

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1.Background

2.Basic Physics

3.Applications

4.MINT Nano-MOKE



Magnetic Bubble Memory – 1970-80s(YBi)3Fe5O12

Bobeck et al: 13th Annual Conference on Magnetism and Magnetic Materials, Boston, Massachusetts, September 15, 1967.

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M



Magneto-optical Recording 1980-2000s

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Wikipedia



Kerr Signal

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S = R (θk2 + ηk

2)1/2

N = √RS/N = √R (θk

2 + ηk2)1/2



Applications-Magneto-optical Recording-

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Amorphous TbFeCo Thin films

TM(Fe,Co,..) RE(Tb, Dy,..)

<M> = MTM - MRE



Applications-Magneto-optical Recording-

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Magneto-optical Recording

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Magnetic Field Modulation



-Magneto-optical Recording-

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-Magneto-optical Recording-

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Further References

44June 27, 2014

Author: Richard J. Gambino, Takao SuzukiISBN-13: 9780780310094Year: 1999Publisher: Wiley-IEEE Press



Contents

45June 27, 2014

1.Background

2.Basic Physics

3.Applications

4.MINT Nano-MOKE

Nano-MOKE

- 46 - June 27, 2014

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)

- 47 - June 27, 2014

Domains in Permalloy

- 48 -

-78.46 Oe -80.67 Oe -83.07 Oe

-85.49 Oe -87.66 Oe -89.95 Oe

June 27, 2014


Center for Materials for INformation Technology49June 27, 2014

Magneto-Optical Effect and Applications

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