Cunife is an alloy of copper (Cu), nickel (Ni), iron (Fe), and in some cases cobalt (Co). The alloy has the same linear coefficient of expansion as certain types of glass, and thus makes an ideal material for the lead out wires in light bulbs and thermionic valves. Fernico exhibits a similar property. It is a magnetic alloy and can be used for making magnets.
Cunife has a magnetic coercivity of several hundred oersteds. Unlike most high coercivity magnetic materials which are hard and brittle and need to be cast into shape, cunife can be drawn into thin wires. Wires as thin as five thou can be produced this way.
At one point Fender Musical Instruments Corporation used Cunife magnets in their Wide-Range humbucking pickups, however discontinued use, due to Cunife being hard to source.