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Dresden 2011 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 35: Spin Structures/ Skyrmions (jointly with TT) - Invited Talks

MA 35.4: Hauptvortrag

Mittwoch, 16. März 2011, 15:30–16:00, HSZ 04

Complex Magnetic Phase Diagram of the cubic Helimagnet FeGe — •Heribert Wilhelm — Diamond Light Source Ltd., Chilton, Didcot, OX11 0DE, United Kingdom

Cubic FeGe (B20 structure type) shows helical order below Tc=278.3 K. Depending on temperature and magnetic field a complex sequence of cross-overs and phase transitions in the vicinity of Tc has been observed in magnetization and ac-susceptibility measurements in fields parallel to the [100] direction. In a narrow temperature range below Tc several magnetic phases have been found before the field-polarized state occurs. Of particular interest is the so-called A-phase. It splits in at least two distinct areas, A1 and A2. This has been confirmed by small-angle neutron scattering data. These data also yield a hexagonal scattering pattern, the fingerprint of a Skyrmion lattice, within the A1 and A2 regions. Precursor phenomena found above Tc display a complex succession of temperature-driven cross-overs and phase transitions before the paramagnetic phase is reached at T0. The low-field state for Tc<T<T0 is probably characterized by some kind of magnetic correlations concluded from nuclear forward scattering data. They revealed that this phase exists up to about 27 GPa, although the helical order is already suppressed at 19 GPa. No signatures of magnetic order have been observed above 30 GPa. Within a phenomenological model for chiral ferromagnets, which includes magnetic anisotropy, Skyrmionic phases and ’confined’ chiral modulations were obtained. The observed precursor phenomena are then a general effect related to the confinement of localized Skyrmionic excitations.

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