Nanomagnetics
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.
One bit
viewed by
magnetic force microscopy
Is it nano?
Well, overall size is ~1mm, but
the bit has smaller details.
Clearly, nano characterization
methods are being used to see
this.
Apoferritin,
your body’s
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.
Types of Magnetism (Sibel Turksen Thesis)
Few subjects are more difficult to
understand than magnetism.
Encyclopedia Britannica
General Hysteresis Plot
M Magnetization
Perfect
Superparamagnet
-M
Magnetization
in opposite direction
Paramagnet, Ferromagnet &
Superparamagnet
Zero Magnetic Field Magnetic Field Applied
Paramagnet
Domain moments align
randomly—no 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 size—
boundary effect.
Domains “find” each other and
now it generates a moment
comparable to Ferromagnet.
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
Paramagnet
Ferromagnet
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.
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.
Suppose some particles do have
magnetic moments.
N
S
N
S
N
S
N
S
They will chain together!
The chain causes high viscosity.
 Magnetorheological effect.
Magnetorheological Effect
A magnetic fluid.
Fluid becomes solid—and reverses!
Just pretty.
Applications to cars.
Civil Engineering Application
Dong Ting Lake Bridge -- China
Health and Home Appliance Applications
Optical Applications
Optical Application Results
An optical surface ground on the OptiPro SX50 is interferometrically characterized
and MRF polished. The first run eliminates SSD while improving figure. The second
run demonstrates MRF capability to further improve an already polished optic.
Smooth to ~30 nm
i.e., l/20 @ l =600 nm
How can this be used? Better lasers? Better laser weapons? Better chances
for cheap, pollution-free nuclear fusion energy?
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.
References
Nanotechnology, edited by G.L. Timp, SpringerVerlag, 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.