Abstract
We report a comprehensive study of the low-level substitution of by effect on the static and dynamic magnetoelectric coupling in (, 0.02, and 0.04). The cationic substitution has a large impact on the balance between competitive magnetic interactions and, as a result, on the stabilization of the magnetic structures and ferroelectric phase at low temperatures. Low-lying electromagnon excitation is activated in the cycloidal modulated antiferromagnetic and ferroelectric phase in , while it is observed up to in the Fe-substituted compounds, pointing at different mechanisms for static and dynamic magnetoelectric coupling. A second electrically active excitation near 40 is explained by means of crystal-field effects. This excitation is observed up to room temperature, and exhibits a remarkable downshift on cooling in Fe-substituted compounds. Both electromagnon and crystal-field excitations are found to be coupled to the polar phonons with frequencies up to 250 . Raman spectroscopy reveals a spin-phonon coupling below in pure , but the temperature where the coupling starts to be relevant increases with Fe concentration and reaches 100 K in . The anomalies in the dependence of magnetic susceptibility above are well accounted for by spin-phonon coupling and crystal-field excitation, coupled to oxygen motions.
2 More- Received 31 December 2022
- Accepted 21 February 2023
DOI:https://doi.org/10.1103/PhysRevB.107.104410
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