Regensburg 2010 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 22: CE: Spin Systems and Itinerant Magnets
TT 22.7: Vortrag
Mittwoch, 24. März 2010, 11:15–11:30, H21
Dynamic topological spin clusters in the paramagnetic phase of MnSi. — •A. Hamann1, D. Lamago1,2, T. Wolf1, H. v. Löhneysen1, and D. Reznik1 — 1Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany — 2Laboratoire Léon Brillouin, CEA Saclay, France
At ambient pressure and below TC spins in MnSi order in a helical ground state with the helix axis pinned by the crystal potential. At high pressure an exotic spin state forms referred to as partial order [1]. It is characterized by translational helical spin order but orientational disorder and the non-Fermi-liquid resistivity appears nearby in the phase diagram.
Our numerical calculations show that in the absence of the pinning potential isotropic near-neighbor chiral spin interactions of MnSi favor a glassy collection of topological spin clusters. These have the spectral signature of partial order. Their stability relative to the helical order increases with increasing temperature, and a competition with these clusters, not conventional fluctuations, melts the helical phase. Our detailed neutron scattering measurements fully confirm this prediction by identifying partial order at ambient pressure. We show that this partial order may explain most of the puzzling properties of MnSi including the two-component phase transition that was revealed by specific heat [2].
[1] C. Pfleiderer, D. Reznik et al., Nature 427, 227 (2004)
[2] S. M. Stishov et al., Phys. Rev. B 76, 052405 (2007)