Ferromagnetic circuits. Ferromagnetic materials
Magnetic circuits

All materials have a permeability very close to or equal to that of a vacuum, with the exception of ferromagnetic materials. These consist of iron, nickel, cobalt and their alloys. They are characterized by a permeability μ _f significantly higher than that of vacuum:

Relative permeability μ _rf = μ _f / μ ₀ varies from 10 to 10,000, depending...