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Question:
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?



Replies:
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 field).

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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