Half-metal

The octet principle, primitive as it may appear, has not only been applied very successfully to the half-metallic Zintl phases, but it is also theoretically well founded (requiring a lot of computational expenditure). Evading the purely metallic state with delocalized electrons in favor of electrons more localized in the anionic partial structure can be understood as the Peierls distortion (cf. Section 10.5). 

In 1730 or before, Georg Brandt prepared a dark blue pigment from an ore found at the Skila copper works (Riddarhytta) in Westmanland (39). Specimens of this fargcobalt are still preserved in the Cederbaum collection at Oskarshamn. Since the first accurate description of metallic cobalt is to be found in Brandt s dissertation on the half-metals in the Acta Literaria et Scientiarum, Sveciae for 1735, it has frequently been stated that cobalt was discovered in that year. Nils Zenz6n has shown, however, that this issue of die Acta was not published until 1739 and that the portion of Brandt s Diarium Chymicum which records his researches fiom the latter part of 1737 to the end of 1738 is merely a Swedish edition of the Dissertatio de semi-metallis. ... 

According to Zenz6n, Brandt stated in his diary for 1741 (which was not edited until 1744)- As there are six kinds of metals, so I have also shown widi reliable experiments, in my dissertation on the half-metals which I presented to the Royal Academy of Sciences in Upsala in 1735, that diere are also six kinds of half-metals. The same dissertation shows that I, dirough my experiments, had the good fortune. . to be the first... 

The other half-metal referred to in the preceding letter was hydro-siderum, a false element which Apothecary Johann Karl Friedrich Meyer of Stettin, Scheele, and M. H. Klaproth later proved to be a phosphate of iron (73, 74, 41). In another of his letters to Hjelm Scheele said, As far as I can judge of your work, it does you all credit (9). Although this correspondence shows that Hjelm must have isolated molybdenum as early as the fall of 1781, his first paper on it was not published until much later. 

Georg Brandt s dissertation on the half metals. Actes Acad. d Upsal, 4, (1735). 

Bands with 0 < < 1/2 or 3/2 half-metallic ferromagnets with full magnetization M = Nn/j,b or N(2 — n)fxb per band orbital, where N is the number of transition-metal atoms per unit volume if narrow enough for total removal of the spin de-... 

According to our calculation, this substance is called a half-metal, and unusual electronic structures in which the spin-up electrons have an energy gap of 2.57 eV and the spin-down electrons show metallic property as described in Figure 18.12 [19]. 

Heusler alloys have a rich variety of apphcations, owing to some of their unique properties. Some of these phases are half-metallic ferromagnets, exhibiting semiconductor properties for the majority-spin electrons and normal metallic behavior for the minority-spin electrons. Therefore, the conduction electrons are completely polarized. The Ni2MnGa phase is used as a magnetic shape memory alloy and single crystals of Cu2MnAl are used to produce monochromatic beams of polarized neutrons. 

Magnetic B-site ordered perovskites are of interest in at least two contexts, half-metallic ferromagnets , which show a large MR due to intergrain effects, and geometric magnetic... 

Sr2FeMo06- While this material has been known since 1963, intense interest was sparked by the announcement of room temperature MR in 1998. The material is ferro or ferrimagnetic with Tc > 400 K and a metallic conductor, Figure 35. This unusual combination of properties can be explained in terms of the half-metallic ferromagnetic electronic structure model. Figure 36. Note that the Fermi... 

Figure 36 Band stmcture calculations for Sr2FeMo06 showing half-metallic ferromagnetic character. (Reprinted with permission from T. Saitoh, M. Nakatake, A. Kakizaki, H. Nakajima, O. Morimoto, Sh. Xu,Y. Moritomo, N. Hamada, Y. Aiura, Phys.Rev., 2002, B66, 035112. 2002 by the American Physical Society)...

In the last decade, study of double perovskites has accelerated with the discovery of tunneling magnetoresistive (TMR) effects in Sr2FeMo06.i56N. Both the magnetism and transport in these oxides is strongly influenced by the cationic nature and the order/disorder of the ions at the B-site. Ferromagnetism and half-metallic properties are often... 

---