The density of states of silicon is shown in the top panel. Si has a band gap between occupied and unoccupied states, but it is nonmagnetic so the spin-up and spin-down densities of states are identical. The Fermi energy (yellow line) lies in the gap. In the middle panel, the spin-up and spin-down densities of states of ferromagnetic iron are shown. Iron has no gap, although the density of states of the spin-up states at the Fermi energy is quite low. At the bottom is a model density of states for half metallic ferromagnet CrO₂, which has an energy gap at the Fermi energy only in the spin-down states.

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© 2001 American Institute of Physics