NiFe or Nife is a general shorthand expression for a mixture of nickel (Ni) and iron (Fe). NiFe is used to describe nickel-iron batteries, various chemical reactions that involve a nickel-iron catalyst or component, and in geology to describe the general composition of the Earth's core.
The affinity of nickel (atomic number 28) and iron (atomic number 26) for one another produce natural occurring alloys, a large number of commercial alloys, and provide a complex electron environment for catalyzing chemical reactions.
Iron and nickel are notable for being the final elements produced by stellar nucleosynthesis, and thus the heaviest elements which do not require a supernova or similarly cataclysmic event for formation. Iron and nickel are therefore the most abundant metals in metallic meteorites and in the dense-metal cores of planets such as Earth.