Theory of Ferromagnetic Transition Temperature of DMS


T. Dietl, H. Ohno, F. Matsukura, J. Cibert, D. Ferrand, "Zener Model Description of Ferromagnetism in Zinc-Blende Magnetic Semiconductors", Science Vol.287, p1019-1022, 2000.

Ferromagnetism in manganese compound semiconductors not only opens prospects for tailoring magnetic and spin-related phenomena in semiconductors with a precision specific to III-V compounds but also addresses a question about the origin of the magnetic interactions that lead to a Curie temperature (T C ) as high as 110 K for a manganese concentration of just 5%. Zener's model of ferromagnetism, originally proposed for transition metals in 1950, can explain T C of Ga 1-x Mn x As and that of its II-VI counterpart Zn 1-x Mn x Te and is used to predict materials with T C exceeding room temperature, an important step toward semiconductor electronics that use both charge and spin.


Fig. 1. Normalized ferromagnetic temperature TFnor as a function of hole concentration. Inset shows an example of the cross-section of the Fermi volume of holes in a ferromagnetic zinc-blende semiconductor: non-zero magnetization leads to a splitting of the valence band into four subbands. This complex valence-band structure was used to determine the mean-field values of TFnor for p-Ga0.95Mn0.05As and p-Zn0.95Mn0.05Te (solid lines), and to establish chemical trends depicted in Fig. 3.



Fig. 2 Curie temperature TC in Zn1-xMnxTe:N for various Mn contents x and hole concentrations p deduced from the Hall resistance at 300 K. The plane with upper crosses corresponds to TC=0. Experimental values are marked by blue spheres (22) and theoretical predictions by the red mesh and attached yellow spheres. According to Eq. 2, TC is determined by a competition between the hole-induced ferromagnetic interactions (characterized by TF depicted in Fig. 1), and the antiferromagnetic interactions, described by -TAF shown by the plane with lower crosses.



Fig. 3 Computed values of the Curie temperature TC for various p-type semiconductors containing 5% of Mn and 3.5x1020 holes per cm3.