PX157 - C10a - classification of materials

inside the material, the atoms behave as magnetic dipoles, arising from the electron orbital angular momentum round the nucleus or from the electron spin (paramagnetism) or from the charges in induced orbital moment (diamagnetism)
magnetic dipoles may be organized by an applied external magnetic field or permanently organized
many small dipoles create a surface current and inside the material, the net current is zero

eg: imposing an external magnetic field, ${\vec{B}}_{0}$
- ${\vec{B}}_{0}$ induces atomic $\vec{μ}$ , and causes permanent atomic $\vec{μ}$ to align
- an additional magnetic field (dipole field) is generated
- consequently:

\vec{B} = μ_{r} {\vec{B}}_{0}

where, $μ_{r} =$ relative permeability