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Magnetic Metals
Name: Greg M
Status: educator
Age: 40s
Location: N/A
Country: N/A
Date: Around 1999
Question:
What is special (para or di magnetism? unpaired e-?)
about Co, Ni and Fe that make them magnetic?
I figure it is somehow related to electronic structure, but I cannot
figure how this might
relate to the formation of domains... many thanks...
Replies:
I don't think it's related to the electronic structure of the atoms,
if that is what you mean. The presence of unpaired spins allows for
paramagnetism, the tendency of a material to respond to an applied
magnetic field by producing a field of its own (the unpaired spins
line up with the applied field, and generate a field of their own).
But what you are asking about is ferromagnetism, where spins
spontaneously line up in large domains. This occurs whenever the
force unpaired spins exert on one another is stronger than the random
thermal jiggling due to their environment. This depends on the nature
of the crystal lattice the spins find themselves in, clearly. I have
the feeling, however, that the coupling is not directly through space,
but via a response in the electric charge distribution. That is, one
spin produces slight currents in the electron, and then these currents
affect the other spin.
So what you would be talking about is a measure of the (many-body)
electronic contribution to the spin-spin coupling constant in a
crystal. You might be able to get an estimate of this by assuming the
electrons form an ideal Fermi gas, and then do perturbation theory to
second order in the electron spin magnetic moment. It would not be a
straightforward project, if these terms do not already make sense to
you.
In any event, ferromagnetism is squarely a condensed phase
phenomenon, and to understand it you need to understand solid-state
physics -- understanding the properties of the atoms alone is
insufficient.
Grayce
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Update: February 2012
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