Download Lecture 7 ECEN 5341 01-30-2013

Lecture 10 ECEN 5341
02-03-2016
Chapter 3 and 4
Frank Barnes
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Magnetic Materials
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1. Diamagnetic
2. Paramagnetic
3. Ferromagnetic
4. Antiferromagnetic
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Diamagnetic Materials
• 1. Electron spins are paired one up, one down
2. The magnetic moments are from the orbital motion
of the electrons. The sign of the magnetic moment is
negative.
3.Most biological materials are diamagnetic and these
materials are weakly repelled by in a magnetic field
gradient.
4. Superconductors are diamagnetic and you can float a
magnetic above a superconducting plate
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A Superconductor is a perfect
magnetic shield.
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The Moses Effect
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Paramagnetic Materials
• 1 Paramagnetic materials are attracted by a magnetic field
gradient.
• 2. These materials have net magnetic moments but on the
average to zero as a result of the thermal energy.
• 3. At low fields the net magnetic moment is proportional to
the applied magnetic field.
• 4. The magnetic moment saturates at high fields.
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Pierre Curie and is known as Curie ’s law:
M =H ¼ X ¼ C =T
– where M is the magnetization, H is the applied magnetic field,
X is the magnetic susceptibility,
– T is the temperature, and C is the Curie constant and is related
to the magnetic proper ties of the material
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Magnetic Field Effects
Paramagnetic materials have permeate magnetic moments
Spin Alignment for Paramagnetic Materials
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Ferromagnetic Materials
• 1 There are coupled spins in an inner shell of
atoms such as iron. In Iron the exchange
energy parallels four electron spins. This is a
strong enough magnetic moment to align
blocks of atoms.
• 2. The magnetic susceptibility is positive.
• 3. Ferromagnetic material have magnetic
moments even after the field is removed and
hysteresis below a given temperature.
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Ferromagnetic Spins Align
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Antiferromagnetic Material
• These materials can have net magnetic
moment.
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Ferrimagnetic Materials
• This the case for Fe3O4 which had Fe2+ and
Fe3+ in the lattice. This is a bio manufactured
material
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Temperature Dependence of
Ferromagnetic Materials
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Energy Barrier for Superparamagnetic
Material
• 1 Spins flip as a group with thermal energy
≈10-9seconds
Remanent magnetic field
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Biological Magnet
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FIGURE 4.7
Model of the ferritin protein showing the peptide subunits and iron transport
channels. (From www.chemistry
wustl.edu/edudev/LabTutorials/Ferritin/FerritinTutorial.html. With permission
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.)
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Iron in the Body
• In organisms, iron is stored as the mineral ferrihydrite
(5Fe2O3 9H2O) with in the iron storage protein ferritin.
It consists of a 12-nm hollow spherical protein shell
made up of 24 subunits (Figure 4.7). The core of
• ferritin protein is 8 nm in diameter, and it can hold up
to 4500 iron atoms in the form of ferrihydrite. Iron is
transported into and out of the core through threeand fourfold channels in the shell. During transport,
highly toxic Fe(II ) is oxidized to Fe( III) for storage
• as ferrihydrite (Harrison and Arosio, 1996).
• Ferrihydrite is a superparamagnetic antiferromagnet
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Magnetite (Fe3O4)
a ferromagnetic iron oxide
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Transmission electron micrograph of the magnetotactic bacterium MS-1 (top).
(From www.calpoly.edu/
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rfrankel/mtbphoto.html
)
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Biogenic magnetite extracted from the human hippocampus (bottom).
(From Schultheiss-Grassi, PP, R Wessiken, and J Dobson (1999) Biochim.
Biophys. Acta 1426 : 212–216. With permission.)
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Hemoglobin
μeff= 5.35 B per heme group.
[Wadas 1991].
Figure 7 The structure of hemoglobin,
www.elp.manchester.ac.uk
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