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arXiv · 2608.01892

Microscopic magnetic phase evolution in the Weyl semimetal Mn$_3$Sn revealed by $\mu^+$SR

U. Miniotaite·O. K. Forslund·H. Luetkens·V. Rai·J. Persson·G. D. Morris·D. Zuhair·D. W. Tam·S. Nandi·Y. Sassa·M. Månsson
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Abstract

We report a comprehensive muon spin relaxation ($\mu^+$SR) and bulk magnetization study of the antiferromagnetic (AFM) Weyl semimetal Mn$_3$Sn (composition Mn${2.99}$Sn). Mn$3$Sn is reported to exhibit a commensurate inverse triangular (IT) AFM phase, an incommensurate (IC) helical AFM phase, and a proposed low-temperature spin-glass-like state. In our sample, we identify the characteristic temperatures associated with these regimes as N'eel temperature ($T\mathrm{N} = 418$ K), a macroscopic bulk transition temperature between IT-AFM to IC helical phase ($T\mathrm{t} \approx 275$ K), and low-temperature transition $T_\mathrm{f} = 21$ K. Investigating the low-temperature regime below $T_\mathrm{f}$, we find no evidence of a static spin-glass state. Instead, the sample exhibits an increasing ferromagnetic (FM) component accompanied by a localized slowing of spin fluctuations, indicating that these phenomena may be decoupled. In the IC helical AFM phase, the zero-field (ZF) spectra are best described by damped oscillations with an empirical phase offset, consistent with anharmonic and amplitude-modulated order reported by scattering studies. Upon warming above 150 K, a continuous redistribution of muon spectral weight reveals a broad, homogeneous magnetic crossover between the IC helical and IT-AFM phases. In the commensurate IT-AFM phase above $T_\mathrm{t}$, a persistent missing fraction in the initial asymmetry indicates that a subset of implanted muons, corresponding to roughly 20% of the sample-related asymmetry, undergoes unresolved ultrafast depolarization. Finally, we observe temperature-driven shifts in muon site populations above 325 K. Ultimately, our results show a highly dynamic magnetic landscape in Mn$_3$Sn, demonstrating how its complex magnetic orders often coexist and evolve continuously with temperature.

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U. Miniotaite, O. K. Forslund, H. Luetkens, V. Rai, J. Persson, G. D. Morris, D. Zuhair, D. W. Tam, S. Nandi, Y. Sassa, M. Månsson. 2026-08-03. Microscopic magnetic phase evolution in the Weyl semimetal Mn$_3$Sn revealed by $\mu^+$SR. https://doi.org/10.1103/t9y2-h8th

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