Question

Discuss the physical significance of the equivalent magnetization current densities J_m and J_ms.

Can we utilize them as current sources to run a circuit? If YES/NO, why do you think so?

Answer 1

Macroscopic currents flowing in wires cause magnetic fied at surrounding points.

Magnetic diole moment of these wires is defined as , where is area vector of loops of wires.

When a material is subjected to external magnetic field, the atoms and electrons react to this magnetic field.

Electrons also possess magnetic dipole moment due to spin and when the spin of electrons is paired so that one electron's spin is up and other electron's spin is down, net magnetic dipole moment is zero. But in some substances there are unpaired electrons, the magnetic dipole moments of these unpaired electrons tends to line up with applied magnetic field, causing paramagnetism.

Orbital motion of the electrons around the nuclei also gets changed such that there will be a dipole moment opposite to the apllied field. This is called diamagnetism.

The magnetic dipole moment per unit volume of a substance is defined as Magnetization

The usual currents (due to flow of electrons) are described in terms of current density such that current flowing through a surface is

The magnetic field caused by spin magnetic dipole moments of unpaired electrons and orbital magnetic dipole moments of electrons can also be described in terms of equivalent magnetization current densities.

Imagine a substance as a collection of tiny current loops all placed one beside the other or atop the other. At the points where the loops touch each other, their currents are in opposite directions and they get cancelled, leaving only a surface current at the boundaries. This gives surface density of magnetization currents .

When magnetization is uniform, only the above surface density will be present. But when magnetization is non-uniform, there will be a volume density of magnetization currents , in addition to the above.

These currents are microscopic, they cannot be used to run a circuit as there is no macroscopic flow of electrons.