Frances HELLOGO.GIFellman Group

Amorphous and nanostructured Silicon
Fe/Cr Multilayers
Magnetic Oxides
Magnetic semiconductors
Magnetic Molecules
Magnetic Oxides

There has been great interest in the utilizing of physical properties of magneto-electronics which is a new developing field, where the two degrees of freedom, the charge and the spin of the carriers, are utilized simultaneously to create new functionalities.  Many promising applications of ferromagnetic semiconductors have been already demonstrated for (Ga,Mn)As, but the low Curie temperature (<110 K) prohibited the operation at room temperature. Recently oxide semiconductors doped with transition metal magnetic impurities, called diluted magnetic oxides such as TiO2, ZnO and SnO2, have attracted much attention due to their potential for high Curie temperatures.

Given that the carries in magnetic oxides reside in an insulating impurity band, there are essentially four kinds of carrier-mediated magnetic exchange interactions which could potentially lead intrinsic carrier-mediated ferromagnetism: double exchange in the impurity [1], bound magnetic polarons percolation [2], indirect exchange coupling mediated by free carriers [3], and hydrogen mediated spin-spin exchange [4]. However, there is currently no consensus on the origin of ferromagnetism in the oxide-dilute magnetic semiconductor.

We are studying on ZnO based diluted magnetic oxide semiconductor which is grown by e-beam evaporator and sputtering system.  Epitaxial film on crystal substrate is grown at high temperature and it is characterized by high-resolution x-ray diffraction.  The magnetism is controlled by carrier density though electron accumulation.

[1] C. Zener, Phys. Rev. 82, 402405 (1951).

[2] A. Kaminski and S. Das Sarma, Phys. Rev. Lett. 88, 247202 (2002).

[3] D. J. Priour, Jr., E. H. Hwang, and S. Das Sarma, Phys. Rev. Lett. 92, 117201 (2004).

[4] C. H. Park and D. J. Chadi, Phys. Rev. Lett. 94, 127204 (2005).