A term in chemistry and spintronics: half-metal for a material with an energy gap depending on electron spin direction

Metals differ from other chemical elements of the periodic table by their electrical and magnetic properties. A typical metal is characterized by good or excellent electrical conductivity, while the spins of the delocalized electrons in the lattice structure of the metal atoms are oriented without preference for a certain, singular direction. In contrast, a half-metal is only conducting when the spins of all electrons are aligned in one direction. It is insulating when their alignment is in opposite orientation. A half-metal is characterized by the presence of an energy gap at the Fermi level for only one electron spin direction, while the energy band for the opposite spin direction is continuous [1]. 

Half-metallic behavior is found in alloys and metal compounds. Examples include Heusler alloys (ferromagnetic alloys with a Heusler phase),  Fe₃O₄ (magnetite) and CrO₂ [1-4].

Keywords: electronic materials, ferromagnetic materials, electrical conductivity, magnetoresistance

References and more to explore
[1] D. V. Talapin, J.-S. Lee, M. V. Kovalenko and E. V. Shevchenko: Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications. Chem. Rev. 2010, 110, 389-458. DOI: 10.1021/cr900137k; see page 410 for discussion of half-metals.
[2] I. Galanakis and Ph. Mavropoulos: Spin-polarization and electronic properties of half-metallic Heusler alloys calculated from first principle. J. Phys.: Condens. Matter 2007, 19, 315213 (16pp) [www2.fz-juelich.de/iff/datapool/iffnews/2008_03_12_TOP_PAPER_2.pdf].
[3] J. Pierre and L. Ranno: Half Metallic Ferromagnets. Laboratoire Louis Neel, CNRS, Grenoble [www.tcd.ie/Physics/People/Michael.Coey/oxsen/newsletter/january98/halfmeta.htm].
[4] I. I. Mazin, D. J. Singh and C. Ambrosch-Draxl: Transport, optical, and electronic properties of the half-metal CrO2. Phys. Rev. B. 1999, 59, 411-418 [prb.aps.org/abstract/PRB/v59/i1/p411_1].