Unpaired Electrons and Magnetism
I understand that paramagnetic is when a metal has a weak
attraction towards a magnet and ferromagnetic is a strong
attraction. I was wondering, if a metal has many unpaired electrons,
does it mean it has a strong attraction and is therefore ferromagnetic?
No, the distinction is not just a matter of degree, "strong" versus "weak."
Paramagnetic materials have unpaired electrons, which means that there exist
electrons that are not spin-locked with others to make a pair with zero net
magnetic moment. The unpaired electrons can be in any orientation, and in fact
will tend to be randomly oriented, to give no net magnetism for a bulk sample.
However, in a magnetic field, some of the spins can align (essentially, the north
poles of their magnets point toward the south pole of the magnet creating the
Ferromagnetic materials have unpaired electrons, but they are NOT randomly
aligned. The electrons orbitally interact so that they actually align in the
same orientation. This makes these groups of electrons (domains)essentially
bar magnets. The reason that ferromagnetic materials are not always bulk magnets
is that these domains are usually randomly aligned, so that on the whole they
cancel out to zero bulk magnetism. An external magnetic field causes spins near
a favorably-oriented domain to join it, so that the domains aligned with the
field grow at the expense of others. This gives the sample a bulk magnetic
orientation: it becomes a magnet.
Richard Barrans, Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming
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Update: June 2012