Study of photoinduced Ferromagnetism in diluted Magnetic Semiconductor (Ga,Mn)As
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Date
2010-06
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Addis Ababa University
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 ®, in which an increase in this coupling is found
to decrease Cmag, 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, magnetizationM(T)=M(0), ferromagnetic
transition temperature TC and magnon specific heat capacity Cmag are plotted and
compared with available experimental observations
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Study of photoinduced Ferromagnetism