DIAMAGNETIC MATERIALS--- When brought into an external field, a weak internal B field is induced inside the material that opposes the external field. |
PARAMAGNETIC MATERIALS--- Brought into an external
magnetic field, the atoms of the material weakly align
with the field. Liquid oxygen provides a classic
demonstration, adhering to the pole faces of a large
magnet. This is like a very, very weak form of
ferromagnetism. |
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FERROMAGNETIC MATERIALS--- contain "unpaired" electrons whose magnetic moments align with those of neighboring atoms. When a ferromagnetic material is brought into an external field, it develops a strong internal field due to electron moments aligning with the field. When the field is removed, most of the alignment still remains, and the material is "permanently" magnetized. |
Magnetic susceptibility is defined by χ = Bmat/Bvac. The magnetic permeability is then μ = μ0[1 + χ]. For ferromagnets, χ is of the order of 1000 or more. For paramagnets (most materials), χ is very small, typically 10-4 or less. For diamagnets, χ is small and also negative.
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