Phenomenology of material magnetism
Magnetic measurements - Principles andproduction of magnetic fields

From the point of view of magnetic properties, a material sample is basically described as a set of magnetic moments resulting from the movement of electrons. It can be said that there are internal currents (Amperian currents) of quantum origin, resulting from the atomic-scale trajectories of electrons, which carry no charge flux through the body and therefore behave like a solenoid. Because of this property, their density j _M (r ) can be expressed as the rotational of another vector function M ( r ).