Ferromagnetism In Diluted Magnetic Semiconductors At Low Carrier Densities
IRG 1: M. Berciu, M. Kennett, X. Wan, R. N. Bhatt
Diluted Magnetic Semiconductors (DMS), such as (Ga,Mn)As and related compounds, are prime candidates for the newly emerging field of Spintronics [1], because of the observation of ferromagnetism at relatively high temperatures, including some reports exceeding room temperature. We have studied the phenomenon of ferromagnetism in DMS at low carrier densities, when the carriers are in an impurity band [2-3] for both III-V ( e.g. (Ga,Mn)As ) and II-VI ( e.g. (Cd,Mn)Te ) based semiconductors. We find that the ferromagnetism can be quite inhomogeneous both in the insulating phase and the weakly metallic phase. This leads to unusual thermodynamic and magnetic properties (such as low bulk magnetization, and large spin entropy down to fairly low temperatures). However, the prognosis for carrier transport appears to be very good because injected carriers appear to be transported along a well magnetized backbone of a percolating magnetic cluster. Related materials are currently under study[4].
References:
[1] S. Das Sarma, Spintronics, American Scientist 89, 516 (2001).
[2] M. Berciu and R. N. Bhatt, Effects of Disorder on Ferromagnetism in Diluted Magnetic Semiconductors, Phys. Rev. Lett. 87, 107203 (2001).
[3] R. N. Bhatt, M. Berciu, M. Kennett and X. Wan, Diluted Magnetic Semiconductors in the Low Carrier Density Regime, Journal of Superconductivity: Incorporating Novel Magnetism 15, 71 (2002); cond-mat/0111184
[4] Wei-Li Lee, T. Pray, K.A. Regan, R.J. Cava, R.N. Bhatt and N.P. Ong, Divergent anomalous Hall effect in the diluted magnetic system Cu(Ga,Mn)Te_2, APS Bulletin (http://www.aps.org/meet/MAR02/baps/abs/S7360004.html).