 The acronym NiFe refers to various chemical reactions that involve an iron–nickel catalyst or component, or in geology, to the general composition of planetary cores (including Earth's).Some iron–nickel alloys are called nickel steel and usually contain additional elements, depending on the purpose.Iron and nickel are notable for being the final elements produced by stellar nucleosynthesis, and the heaviest elements formed with a supernova or similarly cataclysmic event.