The permeability of silicon-iron at very low flux densities

THE initial permeability of magnetic materials is a characteristic of great theoretical as well as practical importance. By definition, the initial permeability is equal to the ratio of the peak value of the flux density to the peak value of the exciting magnetizing field, when the latter approaches the value of zero. Due to the difficulties encountered in measuring the true initial permeability, the term is frequently applied in a rather loose manner to values which have been determined at peak flux density values of 5 gausses or more, or which have been obtained by extrapolating permeability-versus-field strength curves to the zero value of field strength.