Spurious spin nutation modes arising from truncated memory effects
Abstract
Spin dynamics is conventionally treated as inertia-free. The inertial Landau-Lifshitz-Gilbert equation (iLLG) extends this with a second-order time derivative, predicting a high-frequency nutational mode that recent experiments have claimed to observe and interpreted as direct evidence for spin inertia. We show that when spin inertia is generated by eliminating additional dynamical degrees of freedom, the resulting exact spin-only description is generally non-Markovian. The iLLG is recovered as the low-frequency, second-order truncation of the underlying memory kernel. Using a minimal spin--cavity model, we show that the exact eigenfrequencies and those obtained via the iLLG differ and that the spin nutation mode predicted by the latter is a truncation-induced high-frequency artifact. This raises a broader question of the applicability of the iLLG obtained from analogous low-frequency truncations, which may likewise generate spurious high-frequency roots. Consequently, agreement of a high-frequency spectral feature with the iLLG nutation frequency does not, by itself, establish a physical nutation mode.
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BibTeX
@misc{weißenhofer2026spurious,
title = {{Spurious spin nutation modes arising from truncated memory effects}},
author = {Markus Weißenhofer and Ritwik Mondal and M. S. Mrudul and Peter M. Oppeneer},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.27487},
eprint = {2609.27487},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.27487},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Spurious spin nutation modes arising from truncated memory effects
AU - Markus Weißenhofer
AU - Ritwik Mondal
AU - M. S. Mrudul
AU - Peter M. Oppeneer
PY - 2026
DA - 2026/09/23
PB - arXiv
DO - 10.48550/arxiv.2609.27487
UR - https://arxiv.org/abs/2609.27487
AB - Spin dynamics is conventionally treated as inertia-free. The inertial Landau-Lifshitz-Gilbert equation (iLLG) extends this with a second-order time derivative, predicting a high-frequency nutational mode that recent experiments have claimed to observe and interpreted as direct evidence for spin inertia. We show that when spin inertia is generated by eliminating additional dynamical degrees of freedom, the resulting exact spin-only description is generally non-Markovian. The iLLG is recovered as the low-frequency, second-order truncation of the underlying memory kernel. Using a minimal spin--cavity model, we show that the exact eigenfrequencies and those obtained via the iLLG differ and that the spin nutation mode predicted by the latter is a truncation-induced high-frequency artifact. This raises a broader question of the applicability of the iLLG obtained from analogous low-frequency truncations, which may likewise generate spurious high-frequency roots. Consequently, agreement of a high-frequency spectral feature with the iLLG nutation frequency does not, by itself, establish a physical nutation mode.
ER -