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SUMMARY:Fluctuation-driven first order transition in the chiral magnet MnS
 i - Markus Garst\, University of Cologne
DTSTART:20111117T141500Z
DTEND:20111117T151500Z
UID:TALK32773@talks.cam.ac.uk
CONTACT:Dr G Moller
DESCRIPTION:The chiral magnetic metal MnSi possesses various peculiar phas
 es as a function of pressure and magnetic field. At high pressures\, there
  is an extended phase that defies Fermi-liquid theory\, and at a finite ma
 gnetic field a Skyrmion crystal phase -- a regular arrangement of topologi
 cally protected magnetic whirls -- was recently identified. In this talk\,
  we concentrate on the temperature range close to the magnetic transition 
 temperature Tc at ambient pressure\, and we demonstrate that a series of u
 nusual features can be explained in terms of strongly interacting chiral f
 luctuations. We discuss theoretically and experimentally that interactions
  lead to strong renormalization effects resulting in a characteristic cros
 sover temperature T* > Tc where the susceptibility shows a turning point a
 nd the specific heat a crossing point\, also known as Vollhardt invariance
 . More importantly\, the singular interactions drive the chiral transition
  first-order in agreement with Brazovski-theory. Experimentally this is re
 flected in a sharp peak in the specific heat and small discontinuous jump 
 in the temperature dependence of the helimagnetic Bragg peak as measured i
 n small angle neutron scattering. Our theoretical considerations are based
  on basic symmetry principles\, and we expect them to be applicable to a w
 ider range of chiral magnets including Fe{1-x}Co{x}Si\, MnGe or FeGe.
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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