Quantum Hall ferromagnet in magnetically-doped quantum wells

The article reviews our recent studies on quantum Hall ferromagnetism (QHF) in diluted magnetic semiconductors. A giant and nonlinear Zeeman splitting in these materials offers a unique opportunity to examine QHF since crossing of Landau levels (LL) can be achieved in perpendicular magnetic fields. We carried out magnetoresistance studies on modulation-doped, gated heterostructures of Cd1-xMnxTe/Cd1-yMgyTe : I. We put into evidence the formation of Ising quantum Hall ferromagnet with Curie temperature T-C as high as 2 K. QHF in our device is manifested by anomalous magnetoresistance maxima, their hysteretic behavior, and time-dependent resistance, similar to earlier observations in III-V heterostructures. However, in our system these phenomena are much stronger, especially when either 2(-) or 1(-), and 0(+) LL are brought into coincidence. The magnitude of the QHF spikes depends dramatically on the history of the sample, shows hysteresis when either magnetic field or gate voltage are swept, stretched-exponential time evolution characteristic of glassy systems, and strong Barkhausen noise. Our study suggests that these metastabilities stem from the slow dynamics of ferromagnetic domains. (C) 2003 Elsevier B.V. All rights reserved.