Role of magnetic fluids

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Role of magnetic fluids
In the early 20th century
Solid state physics
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Nanoscale science technology
1960
Condensed matter physics
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Including Soft Materials Fluids Liquid
crystals Polymers Emusions Colloids
Nanoparticles Nanostructured materials Nanodevices
Magnetic fluids
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Outline

• What Is Magnetic Fluids (Ferrofluids)?
• Properties of Magnetic Fluids
• Properties of Magnetic Fluid Thin Films under
  Magnetic Fields (perpendicular/parallel)
• Ordered Structures of Magnetic Fluid Films
• Optical Properties of Magnetic Fluid
  Films
• Outlook

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What Is Magnetic Fluids (Ferrofluids) ?
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Properties of Magnetic Fluids
Fundamental Properties
- Magnetic Characterizations -
I ? 0
I 0
H ? I/r
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- Thermal Conductivity -
Magnetic fluid has good thermal
conductivity. (Air 26.2 mW/m/k _at_ T 300 K)
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Applications
- Loudspeaker (high thermal conductivity of MF) -
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- Sealing of magnetic fluids -
S
High-pressure region
Low-pressure region
MF
N
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- Other Applications

• Inkjet printing coding (magnetic particles)
• Surface polishing (nanoparticles)

Most applications are focused on mechanical
purposes.
Applications in bio-medical and
optical-electronics are new interesting topics
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• Preparation of Magnetic Fluids

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FeCl2 FeCl38NaOH ? Fe(OH)2 Fe(OH)3 8NaCl

• Fe(OH)2 2Fe(OH)3 ? Fe3O4 4 H2O

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Properties of Magnetic Fluid Thin Films under
Magnetic Fields (perpendicular/parallel)
Ordered Structures of Magnetic Fluid Films Under
Perpendicular Magnetic Fields Under Parallel
Magnetic Fields Optical Properties of Magnetic
Fluid Films Magnetochromatics (perpendicular) Bire
fringence (parallel) Transmittance
(perpendicular/parallel) Refractive Index
(perpendicular)
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- Formation of Ordered Structure in a Magnetic
Fluid Film -
Top View
glass
Magnetic fluid
Si wafer/ glass
H.E. Horng et al., JAP, 81, 4275(1997)
APL, 75, 2196(1999)
APL, 79, 2360(2001)
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Ordered Structures of Magnetic Fluid Films
Under Perpendicular Magnetic Fields
- Observation of Ordered Structure in a Magnetic
Fluid Film -
Magnetic fluid
Au
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H 53 Oe, d 5.14 ?m
H 77 Oe, d 3.36 ?m
H 34 Oe
H 0 Oe
H ?
H 200 Oe, d 3.36 ?m
H 210 Oe, d 3.27 ?m
H 560 Oe, d 2.37 ?m
H 630 Oe, d 2.37 ?m
?1 ?m, h6 ?m ? 107 108 particles
Ms 5.6 emu/g, T 18.0 ?C, dH/dt 5 Oe/s, L
6 ?m
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????? ?????
H
?
H.E. Horng et al., JAP, 81, 4275(1997)
APL, 75, 2196(1999)
APL, 79, 2360(2001)
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Important Result
Well-controlled and tunable ordered structure
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Magnetochromatic Effects in Magnetic Fluid Thin
Films H.E. Horng, Chin-Yih Hong, Wai Bong Yeung,
and H.C. Yang Cover page of Applied Optics,
Vol. 37, 1 May(1998)
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Optical Properties of Magnetic Fluid Films
Magnetochromatics (perpendicular)
A PC B Camera C Solenoid
D Magnetic fluid film E Mirror
F Telescope G White source H Current
source I Lens J Aperture
C
H.E. Horng et al., Appl. Opt., 37, 2674(1998)
JAP, 83,
6771(1998)
JAP, 88, 5904(2000)
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Under Parallel Magnetic Fields
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Under Parallel Magnetic Fields
H 200 Oe dH/dt 100 Oe/s W 10 µm
L 1.5 µm Ms 17.6 emu/g td 3
min ?x 1.45 µm
H
?x
10 ?m
- Periodic one dimensional grating -
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Magnetochromatics of the Magnetic Fluid Film
under a Dynamic Magnetic Field Herng-Er Horng,
S.Y. Yang, S.L. Lee, Chin-Yih Hong, and H.C.
Yang Appl. Phys. Lett., 79, 350 (2001)
H (Oe)
60
200
? 15.2o
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• Tunable Refractive index

Experimental setup
S.Y. Yang, Y.F. Chen, H.E. Horng, Chin-Yih Hong,
W.S. Tse, and H.C. Yang, APL, 81, 4931(2002)
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We have well controlled and understood the
ordered structures and the optical properties of
the magnetic fluid thin films.
Future Works
Applications of Magnetic Fluids
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Magnetic Field Dependent nMF(H)
The nMF is increased under a higher field. The
increase in nMF is suggested to be due to the
column formation.
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Working Principle
(a) H 0, ncore gt nMF, total reflection occurs
IH0
Magnetic fluid
core
cladding
(b) H ? 0, ncorelt nMF, total reflection vanishes
IH?0
IH?0 lt IH0
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Modulation of Transmitted Light Intensity
L 796 ?m Ms 0.61 emu/g
H (Oe)
Transmission loss ()
Transmission loss (IT-IT,H0)/IT,H0
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- Experimental Setup
H
Transmission axis
Transmission axis
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He-Ne laser (? 632.8 nm)
w/0.01o resolution
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Polarizer
Ein
Eout
Sample
Analyzer
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- Magnetic Field Dependent C-M Rotation -
??-?
? 45o
??-H
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Summary
The refractive index of magnetic fluid films can
well manipulated. The feasibility of the
magnetic-fluid-based optical modulator and switch
is demonstrated.
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• Conclusions

Magnetically labeled immunoassay
Photonic Crystal
Switch
CWDM
Modulator
Magnetic fluids
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Thank you for your attention!