Iron-nickel alloy（Ni-Fe precision alloy）is a low-frequency soft magnetic material with high magnetic permeability and low coercive force in a weak magnetic field. Early iron-nickel alloys were used for telephone communication, and a heat treatment process and vacuum smelting method were used to improve the alloy properties. The magnetic permeability of Ni78% Ni-nickel alloy in weak magnetic field is about 10-20 times higher than that of silicon steel. It is commonly used in sensitive relays, magnetic shielding, telephone and radio transformers, precision AC and DC instruments, and current transformers. In the transformer). By adding elements such as molybdenum, manganese, cobalt, copper, and chromium to the iron-nickel alloy, a ternary or quaternary iron-nickel alloy having a larger initial magnetic permeability μi and a maximum magnetic permeability μm can be obtained.