Half-metal

Not to be confused with semi-metal.

The electronic structure of a half-metal. $E_{f}$ is the Fermi level, $N(E)$ is the density of states for spin down (on the left) and spin up (on the right). In this case, the half-metal is conducting in the minority spin channel.

A half-metal is any substance that acts as a conductor to electrons of one spin orientation, but as an insulator or semiconductor to those of the opposite orientation. Although all half-metals are ferromagnetic (or ferrimagnetic), most ferromagnets are not half-metals. Many of the known examples of half-metals are oxides, sulfides, or Heusler alloys. Types of half-metallic compounds theoretically predicted so far include some Heusler alloys, such as Co₂FeSi, NiMnSb, and PtMnSb; some Si-containing half–Heusler alloys with Curie temperatures over 600 K, such as NiCrSi and PdCrSi; some transition-metal oxides, including rutile structured CrO₂; some perovskites, such as LaMnO₃ and SeMnO₃; and a few more simply structured zincblende (ZB) compounds, including CrAs and superlattices. NiMnSb and CrO₂ have been experimentally determined to be half-metals at very low temperatures.

In half-metals, the valence band for one spin orientation is partially filled while there is a gap in the density of states for the other spin orientation. This results in conducting behavior for only electrons in the first spin orientation. In some half-metals, the majority spin channel is the conducting one while in others the minority channel is.

Half-metals were first described in 1983, as an explanation for the electrical properties of manganese-based Heusler alloys.

Some notable half-metals are chromium(IV) oxide, magnetite, and lanthanum strontium manganite (LSMO), as well as chromium arsenide. Half-metals have attracted some interest for their potential use in spintronics.

Further reading

• Guezlane, M; Baaziz, H; El Haj Hassan, F; Charifi, Z; Djaballah, Y (2016). "Electronic, magnetic and thermal properties of Co2CrxFe1−xX (X=Al, Si) Heusler alloys: First-principles calculations". Journal of Magnetism and Magnetic Materials. 414: 219–26. Bibcode:2016JMMM..414..219G. doi:10.1016/j.jmmm.2016.04.056.
• Son, Young-Woo; Cohen, Marvin L; Louie, Steven G (2006). "Half-metallic graphene nanoribbons". Nature. 444 (7117): 347–9. arXiv:cond-mat/0611600. Bibcode:2006Natur.444..347S. doi:10.1038/nature05180. PMID 17108960. S2CID 52851642.
• http://www-users.york.ac.uk/~ah566/research/half_metals.html
• http://www.tcd.ie/Physics/People/Michael.Coey/oxsen/newsletter/january98/halfmeta.htm