Ferromagnetism in a dilute magnetic semiconductor: Generalized RKKY interaction and spinwave excitations
Abstract
Carriermediated ferromagnetism in a dilute magnetic semiconductor has been studied using (i) a singleimpurity based generalized RudermanKittelKasuyaYosida (RKKY) approach which goes beyond linear response theory, and (ii) a meanfieldplusspinfluctuation approach within a (purely fermionic) Hubbardmodel representation of the magnetic impurities, which incorporates dynamical effects associated with finite frequency spin correlations in the ordered state. Due to a competition between the magnitude of the carrier spin polarization and its oscillation length scale, the ferromagnetic spin coupling is found to be optimized with respect to both hole doping concentration and impuritycarrier spin coupling energy J (or equivalently U). The ferromagnetic transition temperature T_{c}, deteremined within the spinfluctuation theory, corresponds closely with the observed T_{c} values. Positional disorder of magnetic impurities causes significant stiffening of the highenergy spinwave modes. We also explicitly study the stability/instability of the meanfield ferromagnetic state, which highlights the role of competing antiferromagnetic interactions causing spin twisting and noncollinear ferromagnetic ordering.
 Publication:

Physical Review B
 Pub Date:
 December 2003
 DOI:
 10.1103/PhysRevB.68.235208
 arXiv:
 arXiv:condmat/0304557
 Bibcode:
 2003PhRvB..68w5208S
 Keywords:

 75.50.Pp;
 75.30.Ds;
 75.30.Gw;
 Magnetic semiconductors;
 Spin waves;
 Magnetic anisotropy;
 Condensed Matter  Materials Science
 EPrint:
 10 pages, 12 figures