Ferromagnetism in a quantum Hall system due to exchange enhancement in a GaInAs quantum well

We have investigated Ga0.47In0.53As/Al0.48In0.52As quantum well structures at magnetic fields close to the filling factor 1. At the critical current. a bistable and abrupt switching (transition width less than 4 ppm with respect to the filling factor) between quantum Hall conduction and dissipative conduction was observed at filling factors 1 < v < 1.5. As confirmed by Hartree-Fock calculations. we attribute this switching to a feedback effect between the current-dependent population of different spin levels and the exchange-enhanced spin gap, The effect is accompanied by a ferromagnetic memory of the spin polarization when changing the external magnetic field. (C) 2002 Elsevier Science B.V. All rights reserved.