Regensburg 2022 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 21: Correlated Electrons: Poster Session

TT 21.12: Poster

Wednesday, September 7, 2022, 15:00–18:00, P1

Field dependence of the low-energy magnon modes and a spin-cholesteric phase in Sr₃Fe₂O₇ — •Nikolai Pavlovskii¹, Yuliia Tymoshenko¹, Darren C. Peets¹, Alexandre Ivanov², Jacques Ollivier², Bernhard Keimer³, and Dmytro Inosov¹ — ¹TU Dresden, Germany — ²ILL, Grenoble, France — ³MPI for Solid State Research, Stuttgart, Germany

We systematically studied low-energy magnon excitations in the helimagnetically ordered bilayer perovskite Sr₃Fe₂O₇. The magnetic ground state was previously believed to be characterized with a single-q magnetic order parameter that results from a frustration of exchange interactions, resulting in two types of equivalent helimagnetic domains. Our present results suggest that it could be instead a double-q state. Our elastic neutron-scattering measurements in a magnetic field applied along one of the (110) crystal directions further reveal an additional phase transition within the magnetic phase, associated with the destruction of long-range order along the direction orthogonal to the field, leading to an unusual spin-cholesteric magnetic phase that breaks both chiral symmetry and translational symmetry along only one of the crystal directions. In the orthogonal direction, we observe only short-range quasielastic spin dynamics. Across the transition from the magnetically ordered to the spin-cholesteric phase, these slow spin fluctuations fill in the spin gap in the spin-wave spectrum, as we can see in the high-resolution inelastic neutron-scattering spectra, and ultimately dominate the low-energy magnetic excitation spectrum after the long-range magnetic order is destroyed.