Magnetic semiconductor

A more recent review of the properties of this material has been given by von Molnar and Penney (1985 see also von Molnar et al 1983, 1985). Results discussed in this article, involving the effects of disorder and electron-electron interaction, are described in Chapters 5 and 9. Briefly, the semiconductor-to-metal transition in an increasing magnetic field leads to a conductivity, at 300 mK, that increases linearly with H (von Molnar et al 1983). This is shown in Fig. 3.7. Hopping conduction is observed with an index indicating the influence of a Coulomb gap (Washburn et al 1984), and near the transition a temperature dependence of a as a+mT, with m positive (von Molnar et al 1985). 

We shall consider in Chapter 9 the attractive interaction between two spin polarons, and the possible relationship to high-temperature superconductivity. 

Very direct evidence for the existence of bound spin polarons is provided by the work of Torrance et al (1972) on the metal-insulator transition in Eu-rich EuO At low temperatures, when the moments on the Eu ions are ferromagnetically aligned, the electrons in the oxygen vacancies cannot form spin polarons and are present in sufficient concentration to give metallic conduction. Above the Curie temperature the conductivity drops by a factor of order 10 , because the electrons now polarize the surrounding moments, forming spin polarons with higher effective mass. 

There is also evidence for the existence of spin polarons in dilute magnetic semiconductors such as Cdx xMnxTe with x in the range 0-0.8. This is described in the review by Furdyna and Kossut (1988). 

6 A degenerate electron gas in the presence of a magnetic impurity the RKKY 

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Eurdya, J. K. and Kossut, J. (1988) Diluted Magnetic Semiconductors, in Semiconductors and Semimetals, vol. 25, Academic, New York. 

Answer NMR characteristics observed in bulk semiconductors such as electron hyperfine effects in dilute magnetic semiconductors [322-324], Knight shifts [234], and chemical shift differences resulting from alloying [325-327] and possibly different polytypes [322, 328] have been observed at the nanoscale. 

Nanoparticles of dilute magnetic semiconductors have also been studied by NMR. Here one important question is whether the magnetic ion is incorporated into the NC or resides on the surface. The 113Cd MAS-NMR of NCs of Cd0.991Co0.009S with diameters from 3.5 to 29.5 nm showed peaks shifted by electron hyperfine interactions from next-nearest neighbor Co2+ ions, and by comparison with results from bulk samples that were discussed in Sect. 3.5 it was concluded that Co2+ ions occupied Cd2+ sites and were distributed homogeneously ... 

W. Giriat and J.K. Furdyna, Crystal Structure, Composition, and Materials Preparation of Diluted Magnetic Semiconductors... 

Saul Oseroff and Pieter H. Keesom, Magnetic Properties Macroscopic Studies T. Giebultowicz and T.M. Holden, Neutron Scattering Studies of the Magnetic Structure and Dynamics of Diluted Magnetic Semiconductors J. Kossul, Band Structure and Quantum Transport Phenomena in Narrow-Gap Diluted Magnetic Semiconductors... 

A.K. Ramdas and S. Rodriquez, Raman Scattering in Diluted Magnetic Semiconductors P.A. Wolff, Theory of Bound Magnetic Polarons in Semimagnetic Semiconductors... 

A magnetic semiconductor thin him is made by doping ZnO with the 3d3 7 ion Co2+. The crystal hied splitting of the d orbitals in a tetrahedral site is opposite to that in an octahedral site, with the lower pair of levels labeled e and three upper orbitals labeled t2- (a) What is the spin state of the Co2+ ion in ZnO (b) What is the expected magnetic moment on the Co2+ ions (c) The spectrum has an absorption peak at 660 nm. What is the crystal held splitting of the Co2+ ion in the tetrahedral crystal held of ZnO ... 

Dynamics of Diluted Magnetic Semiconductors J. Kossut, Band Structure and Quantum Transport Phenomena in Narrow-Gap Diluted Magnetic Semiconductors... 

Wang Y, Herron N, Moller K, Bein T (1991) 3-Dimensionally Confined Diluted Magnetic Semiconductor Clusters - Znl-Xmnxs. Solid State Commun 77 33-38... 

Levy L, Feltin N, Ingert D, Pileni MP (1997) Three dimensionally diluted magnetic semiconductor clusters Cdl-yMnyS with a range of sizes and compositions Dependence of spectroscopic properties on the synthesis mode. J Phys Chem B 101 9153-9160... 

Levy L, Hochepied JF, Pileni MP (1996) Control of the size and composition of three dimensionally diluted magnetic semiconductor clusters. J Phys Chem 100 18322-18326... 

Cd -vZnvS (48-50) or dilute magnetic semiconductors like Cdi vMn,.S (51,52). Recently, as described later, CdTe has been prepared via a soft chemistry, for the first time. 

Porous glass Porous silica glass formed by sol-gel method) CdS, CdS fe,- Zn jMn.S magnetic semiconductor clusters... 

Three-dimensionally confined Zn,, MnxS magnetic semiconductor clusters were prepared 110... 

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