Monte Carlo study of ferromagnetism in (III,Mn)V semiconductors -: art. no. 165201

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 T-c 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 T-c'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 T-c. For the simplest version of the model, which has a single parabolic band with effective mass m*, the dependence of T-c on m* is sublinear at large masses, in disagreement with the mean-field theory result T(c)proportional tom*.