# SKM 2023 – wissenschaftliches Programm

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# MA: Fachverband Magnetismus

## MA 44: Frustrated Magnets II

### MA 44.7: Vortrag

### Donnerstag, 30. März 2023, 16:45–17:00, HSZ 403

Reentrant topological magnetic order and a spin-cholesteric phase in the Sr_{3}Fe_{2}O_{7} perovskite — •Nikita Andriushin^{1}, Nikolai Pavlovskii^{1}, Yuliia Tymoshenko^{1}, Darren C. Peets^{1}, Alexandre Ivanov^{2}, Jacques Ollivier^{2}, Bernhard Keimer^{3}, Oksana Zaharko^{4}, and Dmytro Inosov^{1} — ^{1}TU Dresden, Germany — ^{2}ILL, Grenoble, France — ^{3}MPI for Solid State Research, Stuttgart, Germany — ^{4}PSI, Villigen, Switzerland

Topologically nontrivial magnetic structures, e.g., skyrmion lattices and magnetic vortex crystals, are well known in noncentrosymmetric materials, so that antisymmetric exchange interactions are allowed. Only recently, topological multi-q magnetic textures that spontaneously break the chiral symmetry, for example three-dimensional hedgehog lattices, were discovered in centrosymmetric compounds, where they are instead driven by frustrated interactions. Here we show that the bilayer perovskite Sr_{3}Fe_{2}O_{7}, previously believed to adopt a simple single-q spin-spiral order, hosts two distinct types of multi-q topological spin textures. Its ground state represents an unusual multi-q spin texture with unequally intense helical spin modulations at the two ordering vectors. It is followed in temperature by a new "spin cholesteric" phase, in which the chiral symmetry is spontaneously broken along one of the crystal directions, but the weaker modulation along the orthogonal direction melts, giving rise to intense short-range dynamical fluctuations. Shortly before the transition to the paramagnetic state, a more conventional skyrmion-lattice order spanned by two equivalent q vectors emerges.