Half-metal

A half-metal is any substance that acts as a conductor to electrons of one spin orientation, but as an insulator to those of the opposite orientation.

Conduction in magnetic materials is due to two types of electron i.e., electrons with spin up electrons with spin down [A. Fert and I.A Campbell, Phys. Rev. Lett. 21, 1190 (1968)] .

In half metals velence band related to one type of these electrons is fully filled and other is partially filled. So only one type of electrons (either spin up or spin down can pass through it) See the band structutre below for half metals

References

*Nature 444, xiii - xiii (16 Nov 2006)