Magnetisation and Magnetic Intensity
The ultimate source of magnetism is the magnetic dipole moment, associated with an atom due to orbital motion and intrinsic spin. This suggests that all substances possess magnetic property as energy material consists of atoms having electrons revolving around the nucleus. magnetization or magnetic polarization is the vector field that expresses the density of permanent or induced magnetic dipole moments in a magnetic material. The origin of the magnetic moments responsible for magnetization can be either microscopic electric currents resulting from the motion of electrons in atoms, or the spin of the electrons or the nuclei. Net magnetization results from the response of a material to an external magnetic field, together with any unbalanced magnetic dipole moments that may be inherent in the material itself.
Where dm is the elementary magnetic moment and dV is the volume element; in other words, the M-field is the distribution of magnetic moments in the region or manifold concerned. This is better illustrated through the following relation .
where m is an ordinary magnetic moment and the triple integral denotes integration over a volume. This makes the M-field completely analogous to the electric polarisation field, or P-field, used to determine the electric dipole moment p generated by a similar region or manifold with such a polarization:
Where dp is the elementary electric dipole moment. Those definitions of P and M as a "moments per unit volume" are widely adopted, though in some cases they can bring to ambiguities and paradoxes.
The M-field is measured in amperes per meter (A/m) in SI units.