Zusammenfassung
We report on Monte Carlo studies of the kinetic exchange model for (III,Mn)V ferromagnetic semiconductors in which S=5/2 local moments, representing Mn2+ ions, are exchange coupled to band electrons. We treat the Mn2+ spin orientations as classical degrees of freedom and use the hybrid Monte Carlo algorithm to explore thermodynamically important Mn spin configurations. The critical temperature Tc ...
Zusammenfassung
We report on Monte Carlo studies of the kinetic exchange model for (III,Mn)V ferromagnetic semiconductors in which S=5/2 local moments, representing Mn2+ ions, are exchange coupled to band electrons. We treat the Mn2+ spin orientations as classical degrees of freedom and use the hybrid Monte Carlo algorithm to explore thermodynamically important Mn spin configurations. The critical temperature Tc of the model is unambiguously signalled in our finite-size simulations by pronounced peaks in fluctuations of both Mn and band carrier total spins. The Tc’s we obtain are, over much of the model’s parameter space, substantially smaller than those estimated using mean-field theory. When mean-field theory fails, short-range magnetic order and finite local carrier spin polarization are present for temperatures substantially larger than Tc. For the simplest version of the model, which has a single parabolic band with effective mass m*, the dependence of Tc on m* is sublinear at large masses, in disagreement with the mean-field theory result Tc∝m*.
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