Nanomagnetics

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Nanomagnetics
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Most people relate magnetics to storage.

• Magnetic storage
• currently 100 Mbits/in2
• at the expected 10 Gbits/in2 an individutal bit
  will be 1000 nm wide by 70 nm long.

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One bitviewed bymagnetic force microscopyIs
it nano?Well, overall size is 1mm, but the bit
has smaller details.Clearly, nano
characterization methods are being used to see
this.
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Apoferritin, your bodys iron storage protein and
precision magnetic system.
Quaternary structure of the protein. The pieces
make an open cavity that can store thousands of
Fe atoms.
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Types of Magnetism (Sibel Turksen Thesis)
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Few subjects are more difficult to understand
than magnetism.

• Encyclopedia Britannica

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General Hysteresis Plot

• Perfect
• Superparamagnet

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Paramagnet, Ferromagnet Superparamagnet
Zero Magnetic Field Magnetic Field Applied
Paramagnet Domain moments align randomlyno net moment. Net moment appears the applied magnetic field helps the domains find each other to become coupled.
Ferromagnet Domain moments coupled (below Curie temp.) to produce strong, permanent moment. Even higher magnetic moment.
Superparamagnet Domain moments that would couple as in Ferromagnet do not do so because of small sizeboundary effect. Domains find each other and now it generates a moment comparable to Ferromagnet.
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Right or wrong.
I think of the superparamagnet as a small
ferromagnet. Because of its small size, the
magnetic moment wanders. When given an order to
align (when a magnetic field is imposed) it
aligns with the same enthusiasm that a
ferromagnet has, which exceeds that of the
paramagnet.
Superparamagnet
Ferromagnet
Paramagnet
Zero field
Applied field
Like the paramagnet, the superparamagnet returns
to zero magnetization when the field is removed.
It does so for a different reason small size,
not intrinsically weak exchange between the
individual moments.
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The bottom line is
Nano scale has a big impact on the magnetic
properties! In a normally ferromagnetic
material, nano scale reduces the moment, but it
can be restored by applying a magnetic field.
The good news switchable interactions! The
bad news There would seem to be a lower limit
to the size of a magnetic particle that can hold
an alignment for data storage.
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Suppose some particles do have magnetic moments.
They will chain together! The chain causes high
viscosity. ? Magnetorheological effect.
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Magnetorheological Effect
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A magnetic fluid.
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Fluid becomes solidand reverses!
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Just pretty.
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Applications to cars.
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Civil Engineering Application
Dong Ting Lake Bridge -- China
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Health and Home Appliance Applications
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Optical Applications
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Optical Application Results
                                                                                                                                                   
An optical surface ground on the OptiPro SX50 is interferometrically characterizedand MRF polished. The first run eliminates SSD while improving figure. The secondrun demonstrates MRF capability to further improve an already polished optic.
Smooth to 30 nm i.e., l/20 _at_ l 600 nm
How can this be used? Better lasers? Better
laser weapons? Better chances for cheap,
pollution-free nuclear fusion energy?
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Conclusion

• It is hard not to be excited about magnetic
  particles!
• Nice convergence of fairly simple chemistry and
  tangible materials science.
• Tomorrow, I will show you the idea we had for
  getting into this field.

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References

• Nanotechnology, edited by G.L. Timp,
  Springer-Verlag, New York, 1998 Chapter 12 by
  Awschawlom and von Molnar, Physical Properties
  of Nanoscale Magnets.
• Lord Corporation Website.
• Center for Optics Manufacturing.
• Sibel Turksen Ph.D. Thesis, LSU, 2005.