We shortly summarize the main results obtained on the ferromagnetic transit
ion induced by a two-dimensional hole gas in II-VI semiconductor quantum we
lls. The growth of CdMnTe-CdMgTe quantum wells and their p-type modulation
doping using nitrogen is described. Magneto-optical spectra exhibit large Z
ecman splitting which allow us to measure the magnetization of the Mn spins
. A spontaneous magnetization is observed below a critical temperature T-c
approximate to 2 K. In the paramagnetic phase the susceptibility is enhance
d and diverges as the temperature is decreased to T-c. These experimental f
indings agree with a simplified treatment of the RKKY interaction, taking i
nto account the low carrier density achieved in semiconductors. In addition
, these systems allow to study the electronic properties of a 2D carrier ga
s with complete polarization at low applied magnetic field, at which the sp
litting into Landau levels can be neglected. (C) 1999 Elsevier Science B.V.
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