Berlin 2005 – scientific programme

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MA: Magnetismus

MA 23: Spinabh
ängiger Transport III

MA 23.4: Talk

Tuesday, March 8, 2005, 11:15–11:30, TU H1028

Disorder-induced resistive anomaly near ferromagnetic phase transitions — •Carsten Timm¹, M.E. Raikh², and Felix von Oppen¹ — ¹Institut für Theoretische Physik, Freie Universität Berlin — ²Department of Physics, University of Utah, Salt Lake City, U.S.A.

The resistive anomaly in disordered itinerant ferromagnets has a long history, dating back to the first observation by Gerlach in 1932. In 1968, Fisher and Langer proposed a theory for this anomaly based on anomalous scaling. We show that the resistivity ρ(T) can exhibit a stronger singularity than predicted in that work. Close to the Curie temperature T_c the correlation length becomes large compared to the mean free path. Then, the quenched disorder is probed by diffusive carriers, which requires one to go beyond the Boltzmann description used in all previous works. Our approach combines ideas from the theory of random media and from mesoscopic physics. Specifically, we find that dρ/dT scales as |T−T_c|^−1/2 assuming Gaussian magnetic fluctuations. Our results are relevant for ferromagnets with low T_c, such as SrRuO₃ or diluted magnetic semiconductors, whose mobility near T_c is limited by disorder.