Study Of Photoinduced Ferromagnetism

Effects of photo-excitation and spin wave scattering on magnetism of the diluted magnetic semiconductor (DMS) (Ga,Mn)As is theoretically studied. The exchange coupling energy between Mn+2 spins local moments is computed starting with the zeeman energy. Its equivalence with the Rudermann-Kittel-Kasuya-Yosida (RKKY) exchange energy which is known to have an oscillatory characteristics and contributing to an indirect exchange, expressed based on the Zener model is described. This energy is shown to rise to maximum near/at resonance. Green function formalism is used to find expression for ferromagnetic transition temperature TC, magnetization and magnetic specific heat Cmag starting with a model Hamiltonian consisting of magnons, photons and an interaction of magnons with photons. TC is indicated for zero impurity concentration, x = 0. Unusual upturn in magnetization and negative magnon specific heat are observed at very low temperature values for larger magnon-photon coupling constant, in which an increase in this coupling is found to decrease Cmag, and enhance the magnetization and the ferromagnetic ordering.