Resistance spikes at transitions between quantum Hall ferromagnets

We report a manifestation of first-order magnetic transitions in two-dimens ional electron systems. This phenomenon occurs in aluminum arsenide quantum wells with sufficiently low carrier densities and appears as a set of hyst eretic spikes in the resistance of a sample placed in crossed parallel and perpendicular magnetic fields, each spike occurring at the transition betwe en states with different partial magnetizations. Our experiments thus indic ate that the presence of magnetic domains at the transition starkly increas es dissipation, an effect also suspected in other ferromagnetic materials. Analysis of the positions of the transition spikes allows us to deduce the change in exchange-correlation energy across the magnetic transition, which in turn will help improve our understanding of metallic ferromagnetism.