In ferromagnets of the iron group, the main role in creating the magnetic moment of the atom is played by the spin magnetic moment. In a first approximation, the magnetic moment of an atom is determined by the algebraic sum of the spin magnetic moments of the electrons of the unfilled shell. So, in an empty 3d iron layer, instead of ten, there are only six electrons, the spins of five of them are directed parallel to each other, and one - antiparallel. Therefore, the resulting magnetic moment of the iron atom should be 4μ6. In fact, the magnetic moment of the iron atom is 2.218μ6. The discrepancy in the values of the moment is due to a violation of the orientation of the spins upon transition to the solid state, associated with interatomic interactions and the overlap of electronic levels of atoms. If a substance is placed in an external magnetic field, then, interacting with the field, the substance will be magnetized.