Geffe, Chernet Amente (2010) Study of Photoinduced Ferromagnetism in Diluted Magnetic Semiconductor (Ga,Mn)As. PhD thesis, Addis Ababa University.
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Abstract
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 fi, in which an increase in this coupling is found to decrease C mag, and enhance the magnetization and the ferromagnetic ordering. There is no observed effect of spin wave scattering on Cmag at lower temperatures which, however, is found to rise faster exceeding scattering absence as temperature increases. Exchange coupling energy Jnm, magnetization M(T)=M(0), ferromagnetic transition temperature TC and magnon specific heat capacity Cmag are plotted and compared with available experimental observations.
| Item Type: | Thesis (PhD) |
|---|---|
| Subjects: | Q Science > Q Science (General) Q Science > QC Physics |
| Divisions: | Africana |
| Depositing User: | Selom Ghislain |
| Date Deposited: | 26 Sep 2018 10:35 |
| Last Modified: | 26 Sep 2018 10:35 |
| URI: | http://thesisbank.jhia.ac.ke/id/eprint/5607 |
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