Posted by Steve Simon on April 19, 2013, 9:47 am, in reply to "Magnetisation in Solids"
Hi Electron Band-it (nice name)
I'm not entirely sure I understand the question, but let me make some statements that might help.
In the band theory of electrons, moments are never "local". From the paramagnetic term of the Hamiltonian, you can have pauli paramagnetism for a metal, but you expect no spin suscpetibility if it is an insulator. From the diamagnetic term of the Hamiltonian, you can also get some diamagnetism. In the band theory of electrons you can have pauli paramagentism and you can diamagnetism, but you can't have spontaneous magnetism like ferro and antiferro.
In order to have localized moments (isolated spins) we must go beyond band theory of electrons. When we invoke strong electron-electron interaction (mott insulator physics for example) then we can get localized moments on atoms. Typically in this case we are talking about an insulator. These moments are always paramagnetic at high temperature. At lower temperature, they can be ferromagnetic or antiferromagnetic depending on the sign of the interaction between the moments.
Finally, one can have magnetism for non-localized moments. This is what we called "itinerant" ferromagentism, and is also a result of electron-electron interaction.
Does that help?
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