H-field and magnet
The H-field is defined as:
- (definition of H in SI units)
With this definition, Ampere's law becomes:
where If represents the 'free current' enclosed by the loop so that the line integral of H does not depend at all on the bound currents. For the differential equivalent of this equation see Maxwell's equations. Ampere's law leads to the boundary condition
where Kf is the surface free current density.
which does not depend on the free currents.
The H-field, therefore, can be separated into two independent parts:
where H0 is the applied magnetic field due only to the free currents and Hd is the demagnetizing field due only to the bound currents.
The magnetic H-field, therefore, re-factors the bound current in terms of 'magnetic charges'. The H field lines loop only around 'free current' and, unlike the magnetic B field, begins and ends near magnetic poles as well.