Regensburg 2007 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 13: Spinstructures and magnetic Phase Transitions
MA 13.4: Vortrag
Dienstag, 27. März 2007, 11:00–11:15, H5
Theory of the helical spin crystal. A candidate for the partially ordered state of MnSi — •Benedikt Binz1,2 and Ashvin Vishwanath2 — 1Institut fuer theoretische Physik, Universitaet zu Koeln — 2Departement of Physics, University of California, Berkeley
Recent experiments in the "partial order" regime at high pressure in MnSi quite intriguingly suggest diffuse spin correlations and slow dynamics in a pure crystalline metal. As a starting point for a theoretical description of this phase, we are investigating the nature of its dominant spin correlations. Particularly, the observed location of maximal neutron scattering intensity around <110> is difficult to explain in terms of fluctuating helical spin-density waves alone. We therefore investigate helical spin crystals. These are magnetic structures obtained by superimposing distinct spin spirals, via a process reminiscent of crystallization. Based on a phenomenological Landau description, we identify which spin crystal structures may be energetically stabilized and study their properties. One of these states, a bcc spin crystal, is compatible with existing data on MnSi from neutron scattering and magnetic field studies. It also shows new and interesting phenomena, such as symmetry stabilized topological textures, missing higher order Bragg reflections and an octupolar order parameter. Possible routes towards "partial order", which requires the destruction of long-range order by some mechanism, will be briefly discussed.