μ_4z or mu4z - initial impedance permeability¹⁾ approximating the value of initial magnetic permeability μ_i obtained by measuring the relative magnetic permeability at the excitation of magnetic field strength H = 4 mA/cm = 0.4 A/m.²⁾

The value μ_4z is related to the initial permeability μ4, and depending on the exact definition can mean the same value.

The letter “z” in the symbol denotes “impedance” (which is itself typically referred to by the capital letter “Z”).

• Types of magnetic permeability