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MA: Fachverband Magnetismus

MA 9: Magnetic Materials I

MA 9.7: Vortrag

Montag, 14. März 2011, 16:15–16:30, HSZ 401

Precursor Phenomena at the Magnetic Ordering of the cubic Helimagnet FeGe — •Michael Baenitz¹, Heribert Wilhelm², Marcus Schmidt¹, Ulrich K. Rößler³, Alexei N. Bogdanov³, and Andrey A. Leonov³ — ¹MPI CPfS, Noethnitzer Str. 40, 01187 Dresden — ²Diamond Light Source Ltd., Chilton, Didcot, OX11 0DE, United Kingdom — ³IFW Dresden, Postfach 270116, 01171 Dresden

We report on detailed magnetic measurements on the cubic helimagnet FeGe in external magnetic fields parallel to the [100] direction and temperatures in the vicinity of the onset of long-range magnetic order at T_c≈ 278 K. Depending on the temperature and field, a helical state (H<H_c1), a conical phase (H_c1<H<H_c2), or the so-called A-phase were observed below H_c2 at which the field-polarized state occurs. Precursor phenomena found above T_c display a complex succession of temperature-driven cross-overs and phase transitions. The A-phase pocket is split in at least two distinct areas, A₁ and A₂. The area A₁ at lower fields shows clear lines of transitions into the conical phase at lower temperature and into the A₂ area at higher fields. The area A₂ appears to transform continuously into the conical phase. Relying on a modified phenomenology for chiral magnets, the A₁ phase could indicate existence of a +π Skyrmion lattice, however, the A₂ phase seems related to helicoids propagating in directions perpendicular to the applied field. We suggest that the observation of this A₂-phase can be explained by hexagonal arrays of spiral domains consisting essentially of helicoids.