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Theory of Ferromagnetic Semiconductors
|Hiroshi Katayama-Yoshida 1, Kazunori Sato 1, Tetsuya Fukushima 1, Masayuki Toyoda 1, Hidetoshi Kizaki 1, Peter H. Dederichs 2|
1. Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan
By using the KKR-CPA method within the local-density approximation, the electronic structure of II-VI and III-V-based DMS is calculated. It is found that the range of the exchange interaction in II-VI and III-N, being dominated by Zener's double exchange mechanism, is very short ranged due to the exponential decay of the impurity wave function in the gap. On the other hand, in (Ga,Mn)As and (Ga,Mn)Sb, where Zener's p-d exchange mechanism dominates, the interaction range is weaker but long ranged, because the extended valence hole states mediate the ferromagnetic interaction. Curie temperatures (Tc's) of DMSs are calculated by using the mean-field approximation (MFA), the random-phase approximation, and the, in principle exact, Monte Carlo method. It is found that the Tc values of (Ga, Mn)N and (Ga,Cr)N are very low since, due to the short-ranged interaction, percolation of the ferromagnetic coupling is difficult to achieve for small concentrations. It is found that the MFA strongly overestimates the Curie temperatures for low concentrations due to shortrangeness of interactions in (Zn,Cr)S, (Zn,Cr)Se and (Zn,Cr)Te. The Curie temperatures of (Zn,Cr)Te calculated by Monte Carlo simulation agree very well with recent experimental values. We show that 2-dimensional (2D) spinodal decomposition under layer-by-layer crystal growth condition leads to characteristic quasi-one-dimensional nano-structures (1D Konbu-Phase) in DMS. We design a new fabrication process in the bottom-up nanotechnology to realize the Tera-bit-density nano-magnets by controlling the self-organized two-dimensional spinodal decomposition. We show that the growth position, shape and density of quasi-one-dimensional nano-magnets in the DMS can be controlled by the nano-scale seeding and the vapor pressure of the doped magnetic-impurities under the thermal non-equilibrium crystal-growth condition in MBE, MOVPE or MOCVD.
Presentation: Invited oral at E-MRS Fall Meeting 2006, Symposium E, by Hiroshi Katayama-Yoshida
See On-line Journal of E-MRS Fall Meeting 2006
Submitted: 2006-05-13 16:10 Revised: 2009-06-07 00:44