Ferromagnetic metal/semiconductor

As a result, nearly perfect interfaces between the ferromagnetic material and the semiconductor are not a prerequisite for efficient spin injection. It is for example possible to insert a non-magnetic seed layer between the ferromagnetic base layer and the semiconductor collector. Since hot electrons retain their spin moment while traversing the thin non-magnetic layer this will not drastically reduce the spin polarization of the injected current. Finally, since electron injection is ballistic in SVT and MTT devices the spin injection efficiency is not fundamentally limited by a substantial conductivity mismatch between metals and semiconductors [161, 162], The latter is the case in diffusive ferromagnetic metal/semiconductor contacts [163],... 

Fert A, Jaffres H (2001) Conditions for efficient spin injection from a ferromagnetic metal into a semiconductor. Phys Rev B 64 184420... 

Oxide pyrochlores of the general formula A2B2O7 show interesting electronic properties (Subramanian et al, 1983). Ferromagnetic pyrochlores of rare earths have also been described (Subramanian et al., 1988). A composition-dependent metal-semiconductor transition has been found in A2(Ru2 (AJ07 j, where A = Bi or Pb (Beyerlein et al., 1988). 

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. 

The essential reason for the failure of spin injeetion from a ferromagnetic metal into a semieonduetor turned out to be the eonduetivity difference between these materials, whieh amounts to several orders of magnitude. It was shown that for the usual parameters of a ferromagnetie metal (i.e. (i) non-eomplete spin-polarisation at the Fermi-level, and (ii) spin-flip length 10 nm) the injeetion of spin-polarised electrons into a semiconductor is prohibited by fundamental laws of eleetrodynamics [6]. This impossibility of spin injection from a ferromagnetic metal into a semiconductor because of its conductance mismateh was derived eonsistently from models, based on electrochemical potential alignment or on a eireuit of parallel conductivity channels for spin-up and spin-down polarisation, respeetively [7]. 

Electrically, ferrites can be classified as somewhere between semiconductors and insulators. In many applications, this is their main advantage over ferromagnetic metals, because their high resistivity results in low energy losses. When an ac field is applied to a conductive material, the fraction of the field absorbed to excite the conduction electrons becomes increasingly important as the frequency increases, at the expense of the field fraction used to magnetise the sample effectively. An accurate calculation of eddy-current losses is extremely complex, because it depends on the detailed domain structure. However, an approximate comparison can be illustrative. Eddy-current losses can be expressed as ... 

Kumar R, Singh A P, Thakur P, Chae K H, Choi W K, Angadi B, Kaushik S D, Patnaik S, Ferromagnetism and metal-semiconductor transition in Fe doped ZnO thin films, J. Phys. D Appl. Phys., 41, 155002, 2008. 

Pet] Petrakovskiy, G.A., Loseva, G.V., Sokolovich, V.V., Ikonnikov, V.P., Baranov, A.V., Ovchinnikov, S.G., High-Temperature Ferromagnetism and die Metal-Semiconductor Transition in an Iron Chromium Thiospinel (in Russian), Zhum. Eksp. i Tear. Fiz., 79,2411-2421 (1980) (Experimental, Crys. Structure, Electr. Prop., Magn. Prop., 10)... 

Schmidt, G., Ferrand, D., Molenkamp, L.W., Filip, A.T. and van Wees, B.J. (2000) Fundamental obstacle for electrical spin inj ection from a ferromagnetic metal into a diffusive semiconductor. Physical Review B Coruiensed Matter, 62, R4790. 

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