Hysteretic resistance spikes in magnetic 2DEGs

We use spin-density-functional theory to study recently reported hysteretic magnetoresistance $\rho_{xx}$ spikes in Mn-based 2D electron gases [Jaroszy\'{n}ski \textit{et al.} Phys. Rev. Lett. \textbf{89}, 266802 (2002)]. We find hysteresis loops in our calculated Landau fan diagrams and total energies signaling quantum-Hall-ferromagnet phase transitions. Spin-dependent exchange-correlation effects are crucial to stabilize the relevant magnetic phases arising from \emph{distinct }symmetry- broken excited- and ground-state solutions of the Kohn-Sham equations. Besides hysteretic spikes in $\rho _{xx}$, we predict \textit{hysteretic dips} in the Hall resistance $ \rho _{xy}$. Finally, we note that our theory \textit{does not} include domain walls. While not ruling out the importance of these, our quantitative agreement with the experiments does highlight the relevance of spin-dependent exchange-correlation effects in magnetic 2DEGs.