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arXiv · 2511.10294

Long-range propagating paramagnon-polaritons in organic free radicals

Sebastian Knauer·Roman Verba·Rostyslav O. Serha·Denys Slobodianiuk·David Schmoll·Andreas Ney·Sergej Demokritov·Andrii Chumak
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Abstract

Materials are commonly distinguished by their magnetic response into diamagnetic, paramagnetic, and magnetically ordered (ferro-, ferri-, and antiferromagnetic) phases. Diamagnets and paramagnets lack spontaneous long-range order, whereas ordered magnets develop such order below their Curie or N\'eel temperature and support single spin-wave excitations (magnons). Magnons have found applications in radio-frequency technologies and computation, magneto-optics, and foundational quantum experiments. Above the Curie/N\'eel temperature, long-range order is lost and the material transitions to a paramagnetic phase, with localised spin alignment in small patches, producing paramagnons with only short-range propagation. Here we show that long-range coherence is preserved in the organic free radical 2,2,6,6-tetramethylpiperidin-1-oxyl above the N\'eel temperature using all-electrical propagating spin-wave spectroscopy in external magnetic fields. We observe coherently excited low-energy paramagnon-polaritons up to $\mathbf{23\,\mathrm{GHz}}$ , propagating over $\mathbf{8\,\mathrm{mm}}$ at supersonic group velocities exceeding $\mathbf{100\,\mathrm{km\,s^{-1}}}$. Using free radicals as magnon carriers integrates organic materials with spintronics and opens the way to organic electronics, dense information storage, and quantum technologies.

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Sebastian Knauer, Roman Verba, Rostyslav O. Serha, Denys Slobodianiuk, David Schmoll, Andreas Ney, Sergej Demokritov, Andrii Chumak. 2025-11-13. Long-range propagating paramagnon-polaritons in organic free radicals. https://arxiv.org/abs/2511.10294

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