Magnetic Permeability

magnetic permeability

Relative increase or decrease in the magnetic field inside a material compared with the magnetic field in which the material is located. In empty space the magnetic permeability is 1, because there is no matter to modify the field. Materials may be classified by the value of their magnetic permeability. Diamagnetic materials (see diamagnetism) have constant relative permeabilities of slightly less than 1. Paramagnetic materials (see paramagnetism) have constant relative permeabilities of slightly more than 1. The relative permeability of ferromagnetic materials (see ferromagnetism) increases as the magnetizing field increases, reaches a maximum, and then decreases. Pure iron and some alloys have relative permeabilities of 100,000 or more.

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magnetic permeability [mag′ned·ik ‚pər·mē·ə′bil·əd·ē]

(electromagnetism)

permeability

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Magnetic Permeability 

a physical quantity that characterizes the relationship between the magnetic induction B and the magnetic field H in a substance. Its designation is JUL; for isotropic substances μ = B/H (in the cgs system of units), or μ = B/μoH (in the International System of Units; μ₀ is the magnetic constant).

For anisotropic solids (crystals) the magnetic permeability is a tensor. It is related to the magnetic susceptibility K by the formula μ = 1 + 4πK (in the cgs system of units), or μ = 1 + K (in the International System of Units), where μ is measured in dimensionless units. For a physical vacuum K = 0 and μ = 1.

For diamagnetic materials K < 0 and μ < 1; for paramagnets and ferromagnets K > 0 and ju > 1. Magnetic permeability is called static or dynamic, respectively, depending on whether μ for ferromagnetic materials is measured in a constant or variable magnetic field. The values of the two types of permeability do not agree, since eddy currents, magnetic viscosity, and resonance phenomena affect the magnetization of ferromagnets in a variable magnetic field. Magnetic permeability is a complicated function of H, and the concepts of differential, initial, and maximum magnetic permeabilityhave been introduced to describe the relationship.

REFERENCE

Vonsovskii, S. V. Magnetizm. Moscow, 1971.

S. V. VONSOVSKII