Half-metallic magnetism

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-... 

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... 

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... 

First-principles calculations have been performed to study the electronic band structure and the magnetic properties for thiazole complex, Fe(thiazole)2Cl2. From the total and the partial density of states and the atomic spin magnetic moments, it was found that Fe(thiazole)2Cl2 is a metallic antiferromagnet and has a half-metallic (HM) ferromagnetic metastable state <2006PLE245>. 

Despite their long pedigree, however, the ewent interest in the Heusler and semi-Heusler alloys was only sparked in 1983 upon the publication of a theoretical paper by de Groot et al [125] in which the prototypical semi-Heusler alloy NiMnSb was predicted to display half-metallic properties. The concept of a half-metal needs to be carefully distinguished from the similar-sounding but entirely different conc ts of Ae semi-metal and the semiconductor. The property of half-metallicity is inextricably linked with the permanent magnetic polarisation of a material, and refers to the case when the electrons at the Fermi level display 100% spin-polarisation. In other words, while the electronic bands of one spin-species cross the Fermi level, those of the other spin-species do not. In the case of half-metallic semi-Heusler alloys, the majority-spin electrons behave as if the material were a good metal, while the minority-spin electrons behave as if the material were an insulator or semiconductor. 

The authors argue that UNiSn endures an order-disorder lattice transition on annealing, and that the ordered lattice is a half-metallic ferromagnet , whereas the disordered component is non-magnetic. 

In this chapter the focus is upon electronic conductivity in perovskites. The electrons in perovskites are believed to be strongly correlated that is, they do not behave as a classical electron gas, but are the subject to electron-electron interactions. This leads to considerable modification of the collective electron behaviour of the conduction electrons, resulting in metal-insulator transitions, high-temperature superconductivity, half-metals and colossal magnetoresistance (CMR). The effects of strong correlation are important for the 3d, 4d and4f elements. In many ways the topics described here are thus a continuation of the previous chapter on magnetic perovskites, and in truth the two subject areas cannot be separated in a hard and fast maimer. 

Mavropoulos Th, Galanakis 1 (2007) A review of the electronic and magnetic properties of tetrahedrally bonded half-metallic ferromagnets. J Phys Cond Matter 19 315221... 

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