Introduction to Half-Metals
In order to exploit 100% spin polarisation induced by spontaneous magnetisation, which is different from magnetic semiconductors (e.g.
, EuO and (Ga,Mn)As) based on the magnetic-filed-induced ferromagnetism due to the Zeeman splitting at low temperature, half-metallic ferromagnets have been intensively investigated recently. The half-metal possesses a bandgap at the Fermi level EF
only for its minority spins, achieving 100% spin polarisation at EF
[see the spin density of states (DOS) in the figure]. Four types of the half-metallic ferromagnets have theoretically been predicted so far; oxide compounds (e.g.
, rutile CrO2
and spinel Fe3
), perovskites (e.g.
), Zinc-blende compounds (e.g.
, CrAs) and Heusler alloys (e.g.
, NiMnSb). Even though both CrO2
have been reported to show almost perfect spin polarisation at low temperature, to date there has been no experimental report on the half-metallicity at room temperature (RT), which is highly required from the viewpoint of device applications.
For further reading
Review on half-metals: I. Galanakis and P. H. Dederichs (Eds.), "Half-metallic Alloys - Fundamentals and Applications" (Springer, Berlin, 2005).
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