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Diamagnets are materials with a magnetic permeability less than μ 0 (a relative permeability less than 1). Consequently, diamagnetism is a form of magnetism that a substance exhibits only in the presence of an externally applied magnetic field. It is generally a quite weak effect in most materials, although superconductors exhibit a strong effect.
where μ 0 is the vacuum permeability (see table of physical constants), and (1 + χ v) is the relative permeability of the material. Thus the volume magnetic susceptibility χ v and the magnetic permeability μ are related by the following formula: = (+).
Highly magnetic materials have a reduced skin depth owing to their large permeability as was pointed out above for the case of iron, despite its poorer conductivity. A practical consequence is seen by users of induction cookers , where some types of stainless steel cookware are unusable because they are not ferromagnetic.
and permeability is defined as above in § Speed of electromagnetic waves in good dielectrics = the permeability of free space = 4π x 10 −7 H/m. = relative magnetic permeability of the material. Nonmagnetic conductive materials such as copper typically have a near 1.
The permeability of ferromagnetic materials is not constant, but depends on H. In saturable materials the relative permeability increases with H to a maximum, then as it approaches saturation inverts and decreases toward one. [2] [3] Different materials have different saturation levels.
The magnetic permeability of diamagnetic materials is less than the permeability of vacuum, μ 0. In most materials, diamagnetism is a weak effect which can be detected only by sensitive laboratory instruments, but a superconductor acts as a strong diamagnet because it entirely expels any magnetic field from its interior (the Meissner effect).
For a magnetic circuit constructed with an air gap or air gaps, the permeability of a hypothetical homogeneous material which would provide the same reluctance; (these "effective" above are sizes of a toroid core made from the same material which has the same magnetic properties as the core); Minimum cross-section, A min; Inductance factor, A L
Relative permeability, , for phase is then defined from =, as = / where is the permeability of the porous medium in single-phase flow, i.e., the absolute ...