  In order to single out dominant phenomena that account for carrier-controlled
magnetism in p-(Cd,Mn)Te quantum wells we have carried out magneto-optical
measurements and Monte Carlo simulations of time dependent magnetization. The
experimental results show that magnetization relaxation is faster than 20 ns in
the paramagnetic state. Decreasing temperature below the Curie temperature Tc
results in an increase of the relaxation time but to less than 10 micro
seconds. This fast relaxation may explain why the spontaneous spin splitting of
electronic states is not accompanied by the presence of non-zero macroscopic
magnetization below Tc. Our Monte Carlo results reproduce the relative change
of the relaxation time on decreasing temperature. At the same time, the
numerical calculations demonstrate that antiferromagnetic spin-spin
interactions, which compete with the hole-mediated long-range ferromagnetic
coupling, play an important role in magnetization relaxation of the system. We
find, in particular, that magnetization dynamics is largely accelerated by the
presence of antiferromagnetic couplings to the Mn spins located outside the
region, where the holes reside. This suggests that macroscopic spontaneous
magnetization should be observable if the thickness of the layer containing
localized spins will be smaller than the extension of the hole wave function.
Furthermore, we study how a spin-independent part of the Mn potential affects
Tc. Our findings show that the alloy disorder potential tends to reduce Tc, the
effect being particularly strong for the attractive potential that leads to
hole localization.
