Perminvar

the name for a group of nickel-iron-cobalt alloys that sometimes contain additives of molybdenum and chromium. Perminvars, which are classified as soft-magnetic materials, are characterized by a low dependence of the magnetic permeability μ on field intensity. They were developed in the USA in the late 1920’s. A typical Perminvar contains 45 percent Ni, 30 percent Fe, and 25 percent Co; the values for μ range from 400 to 500 and remain practically constant in a magnetic field whose strength ranges from 0 to 0.5 and even 1.0 ampere per cm (A/cm). The value of μ and its region of relative constancy can be increased significantly by special heat treatment under an applied magnetic field. For example, after such treatment, the value of μ in Perminvars that contain approximately 47 percent Ni, 30 percent Fe, and 23 percent Co is approximately equal to 1,000, and the variation in μ over a magnetic field that ranges from 0 to 8 A/cm does not exceed 10–15 percent. The saturation magnetization of Perminvars is 1.5 tesla, and the Curie point is 600°C.

Perminvars are used in radioelectronics and communication engineering for producing high-stability transformer cores and choke coils that minimally distort the transformed signal.