Berlin 2012 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 38: Correlated Electrons: Spin Systems and Itinerant Magnets 1
TT 38.9: Vortrag
Donnerstag, 29. März 2012, 12:00–12:15, H 3010
Fluctuation-driven first order transition in the chiral magnets — •M. Garst1, M. Janoschek2,3,4, P. Krautscheid1, A. Bauer3, C. Pfleiderer3, P. Böni3, and R. Georgii3,5 — 1Institut für Theoretische Physik, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln — 2Department of Physics, University of California, San Diego, La Jolla, CA 92093-0354, USA — 3Physik Department E21, Technische Universität München, D-85748 Garching — 4Laboratory for Neutron Scattering, Paul-Scherrer Institut & ETH Zürich, CH-5232 Villigen, PSI, Switzerland — 5Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), Technische Universität München, D-85748 Garching
Chiral magnets such as MnSi, Fe1−xCoxSi, MnGe or FeGe possess a weak Dzyaloshinskii-Moriya spin-orbit interaction that leads to a twist of the magnetization on long length scales resulting in chiral magnetic textures. We discuss theoretically and experimentally how this chiral spin-orbit interaction is reflected in the spin dynamics close to the magnetic transition at Tc in MnSi and related compounds. As the transition is approached chiral fluctuations become soft resulting in neutron scattering intensity concentrated on a sphere in reciprocal space. At a characteristic Ginzburg temperature T*> Tc these fluctuations start to interact strongly resulting in pronounced renormalization effects, causing a turning point in the susceptibility ∂T2 χ(T) = 0 and an invariant point in the specific heat ∂H C(H) = 0, also known as Vollhardt invariance. Perhaps even more importantly, these chiral critical fluctuations drive the magnetic transition at Tc first order consistent with a Brazovskii theory for chiral magnetic fluctuations.