Question of the Week, 7.2.2011
Magnetic semiconductors are semiconductor materials that exhibit both magnetism and semiconductor properties. Magnetic semiconductors, which can be formed by doping or alloying semiconductors with suitable transition metal ions (e.g. Mn), have potential applications in spin electronics, as they provide a simple way to combine spin dependent phenomena with conventional semiconductor operation. Therefore, the study and development of such materials and the origin of ferromagnetic order in systems with low carrier densities and low concentration of magnetic ions, found both in semiconducting and metallic systems, is presently investigated in many laboratories [1]. For those materials optically-induced magnetization and magnetically sensitive optical and electrical properties have been demonstrated at low temperatures but not yet in a range warm enough for real applications [2,3].
One of the way to increase working temperature of such material is to create nanopatricles out of magnetic semiconductor material. Despite some successes, many of these efforts have failed, for reasons that remain unclear. For example, Mn was incorporated into nanocrystals of CdS and ZnSe, but not into CdSe and CdTe -despite comparable bulk solubilities of near 50 per cent [4]. These difficulties, which have hindered development of new nanocrystalline materials, are often attributed to ‘self-purification’, an allegedly intrinsic mechanism whereby impurities are expelled. So if magnetic semiconductors that work at room temperature will be created is still open question.
References:
1. http://www.mpg.de/pdf/europeanWhiteBook/wb_materials.pdf
2. Appl. Phys. Lett. 83, 3575, (2003)
3. Appl. Phys. Lett. 84, 3337, (2004)
4. Erwin, S. C. et al. Nature 91, 436, 2005
Yuriy Khalavka