The permeability-frequency response of 4-79 molybdenum permalloy foils

Foils of 4-79 molybdenum Permalloy have been measured for permeability-frequency characteristics as a function of heat treatment and foil thickness for frequencies up to 30 MHz. The slope of the permeability-frequency curve was found to be -0.7 instead of the -0.5 expected from classical theory. The low-frequency permeability of foils thinner than 0.5 mil decreases rapidly with decreasing thickness. This decrease may be connected with changes in texture, surface roughness, or grain size, all of which were observed.