Speaker
Description
The $\mu$SR method has been widely used in recent years to study ion diffusion in battery materials. In data analysis, a dynamic Kubo-Toyabe function is often used in which the internal magnetic field distribution $n(B)$ fluctuates with frequency $\nu$. The model also presumes that $n(B)$ at the muon site remains constant and uncorrelated between fluctuations [1]. However, it has been pointed out that such assumption does not hold in battery materials [2]. While ions with nuclear magnetic moments $I$, such as, Li$^+$ and Na$^+$, jump around the muon, the other elements forming a framework of the material, such as, Co and Mn ( $I>0$), keep their positions. As a result, finite correlation remains in $n(B)$, which contradicts the above assumption. Furthermore, it has been pointed out that muons themselves also start to diffuse above a certain temperature.
To address this issue, a modified model has recently been proposed in which the autocorrelation function is decomposed into a dynamic and a static part [2,3].
Therefore, we have reanalyzed the past $\mu$SR spectra for Li$_x$CoO$_2$ and Na$_x$CoO$_2$ [4,5] using this extend model.
References
[1] R. S. Hayano et al, Phys. Rev. B 20, 850 (1979)
[2] T. U. Ito, and R. Kadono, J. Phys. Soc. Jpn. 93, 044602 (2024)
[3] Musrfit user-function is available: https://github.com/tuito0/musrfit-dynGssEALF
[4] J. Sugiyama et al, Phys. Rev. Lett. 103, 147602 (2009)
[5] M. Månsson and J. Sugiyama, Phys. Scr. 88, 068509 (2013)
| hiramasa@post.kek.jp | |
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