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arXiv · 2406.16425

Spin order and dynamics in the topological rare-earth germanide semimetals

Yuhao Wang·Zhixuan Zhen·Jing Meng·Igor Plokhikh·Delong Wu·Dariusz J. Gawryluk·Yang Xu·Qingfeng Zhan·Ming Shi·Ekaterina Pomjakushina·Toni Shiroka·Tian Shang
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Abstract

The $RE$Al(Si,Ge) ($RE$ = rare earth) family, known to break both the inversion- and time-reversal symmetries, represents one of the most suitable platforms for investigating the interplay between correlated-electron phenomena and topologically nontrivial bands. Here, we report on systematic magnetic, transport, and muon-spin rotation and relaxation ($\mu$SR) measurements on (Nd,Sm)AlGe single crystals, which exhibit antiferromagnetic (AFM) transitions at $T_\mathrm{N} = 6.1$ and 5.9 K, respectively. In addition, NdAlGe undergoes also an incommensurate-to-commensurate ferrimagnetic transition at 4.5 K. Weak transverse-field $\mu$SR measurements confirm the AFM transitions, featuring a $\sim$90 % magnetic volume fraction. In both cases, zero-field (ZF) $\mu$SR measurements reveal a more disordered internal field distribution in NdAlGe than in SmAlGe, reflected in a larger transverse muon-spin relaxation rate $\lambda^\mathrm{T}$ at $T \ll T_\mathrm{N}$. This may be due to the complex magnetic structure of NdAlGe, which undergoes a series of metamagnetic transitions in an external magnetic field, while SmAlGe shows only a robust AFM order. In NdAlGe, the topological Hall effect (THE) appears between the first and the second metamagnetic transitions for $H \parallel c$, while it is absent in SmAlGe. Such THE in NdAlGe is most likely attributed to the field-induced topological spin textures. The longitudinal muon-spin relaxation rate $\lambda^\mathrm{L}(T)$, diverges near the AFM order, followed by a clear drop at $T < T_\mathrm{N}$. In the magnetically ordered state, spin fluctuations are significantly stronger in NdAlGe than in SmAlGe. In general, our longitudinal-field $\mu$SR data indicate vigorous spin fluctuations in NdAlGe, thus providing valuable insights into the origin of THE and of the possible topological spin textures in $RE$Al(Si,Ge) Weyl semimetals.

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Yuhao Wang, Zhixuan Zhen, Jing Meng, Igor Plokhikh, Delong Wu, Dariusz J. Gawryluk, Yang Xu, Qingfeng Zhan, Ming Shi, Ekaterina Pomjakushina, Toni Shiroka, Tian Shang. 2024-06-24. Spin order and dynamics in the topological rare-earth germanide semimetals. https://doi.org/10.1007/s11433-024-2438-9

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