Magnetic Properties
Materials may be classified by their response to externally applied magnetic fields as diamagnetic, paramagnetic, or ferromagnetic. These magnetic responses differ greatly in strength. Diamagnetism is a property of all materials and opposes applied magnetic fields, but is very weak. .It is a class of physical phenomena that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments. Every material is influenced to some extent by a magnetic field. The most familiar effect is on permanent magnets, which have persistent magnetic moments caused by ferromagnetism. The prefix ferro- refers to iron, because permanent magnetism was first observed in a form of natural iron ore called magnetite, Fe3O4. Most materials do not have permanent moments.
Sources of magnetism
Electric current
Spin magnetic moments of elementary particles.
The magnetization of a material is expressed in terms of density of net magnetic dipole moments m in the material. We define a vector quantity called the magnetization M by
$$ M = \frac {μ _{total}} {V} $$Then the total magnatic field N in the material is given by .
B = B0 + μ0M
where μ0 is the magnetic permeability of space and B0 is the externally applied magnetic field.
