Pre-Quantum Electrodynamics

{\bf Magnetization}: magnetic dipole moment per unit volume, denoted by \({\bf M}\).

\({\bf M}\) parallel to \({\bf B}\): {\bf paramagnets}
\({\bf M}\) antiparallel to \({\bf B}\): {\bf diamagnets}
\({\bf M} \neq 0\) even if \({\bf B} = 0\): {\bf ferromagnets}