Half-metal

Not to be confused with semi-metal.
The electronic structure of a half-metal. is the Fermi level, 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.[1] 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.[2]

Half-metals were first described in 1983, as an explanation for the electrical properties of manganese-based Heusler alloys.[3]

Some notable half-metals are chromium(IV) oxide, magnetite, and lanthanum strontium manganite (LSMO),[1] as well as chromium arsenide. Half-metals have attracted some interest for their potential use in spintronics.

In July 2025, researchers reported the first experimental realization of a two-dimensional (2D) half-metal: a bilayer FePd alloy grown on a Pd(001) substrate.[4] This system, composed of only two atomic layers, exhibits complete spin polarization at the Fermi level, as demonstrated by momentum and spin-resolved photoelectron spectroscopy. The half-metallicity is confined to the two-atomic-layer limit and modulated by the Fe-Pd content within the bilayer.[4] The FePd bilayer remains half-metallic at room temperature, is structurally robust, and exhibits tunable electronic properties through variation in Fe content. These features make it a promising platform for nanoscale spintronic applications such as spin filters and spin–orbit torque devices.

References

  1. ^ a b Coey, J.M.D.; Venkatesan, M. (2002). "Half-metallic ferromagnetism: Example of CrO2". Journal of Applied Physics. 91 (10): 8345–50. Bibcode:2002JAP....91.8345C. doi:10.1063/1.1447879.
  2. ^ Rostami, Mohammad; Afkani, Mohammad; Torkamani, Mohammad Reza; Kanjouri, Faramarz (2020-07-01). "Bulk and surface DFT investigations of the electronic and magnetic properties of CsXNO (X = Mg, Ca and Sr) quaternary Heusler alloys". Materials Chemistry and Physics. 248: 122923. doi:10.1016/j.matchemphys.2020.122923. ISSN 0254-0584.
  3. ^ de Groot, R. A.; Mueller, F. M.; Engen, P. G. van; Buschow, K. H. J. (20 June 1983). "New Class of Materials: Half-Metallic Ferromagnets" (PDF). Physical Review Letters. 50 (25): 2024–2027. Bibcode:1983PhRvL..50.2024D. doi:10.1103/PhysRevLett.50.2024. hdl:11370/e3946f6b-8acb-4e0a-80cf-735506203f25.
  4. ^ a b Tan, X. L. (2025-07-16). "Exchange Engineering of a Two‑Dimensional Half‑Metal". Physical Review Letters. 135 (3): 036703. doi:10.1103/mx46-85zf.

Further reading


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