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The iron-chalcogenide FeSe exhibits various electronic states such as superconductivity, the so-called electronic nematicity, as well as a magnetic order under hydrostatic pressure. Therefore, this system attracts considerable research attention in an effort to understand the interplay between the different electronic states. In S-substituted thin films of FeSe$_{1-x}$S$_x$ in which positive chemical pressure is induced by the smaller S substitution for larger Se, we formerly found a kink in the temperature dependence of the electrical resistivity at highly S-substituted thin films of $x \ge 0.18$ without the nematic state [1]. The kink has been observed around the magnetic transition temperature $T_N$ in bulk FeSe under pressure [2]. To investigate the possible magnetism in FeSe$_{1-x}$S$_x$ and compare with Te-substituted FeSe$_{1-y}$Te$_y$ in which negative chemical pressure is induced, we performed muon-spin-relaxation ($\mu$SR) measurements [3].
Zero-field $\mu$SR time spectra of FeSe$_{1-x}$S$_x$ with $x=0.3$ and $0.4$ revealed the formation of a short-range magnetic order at low temperatures. The value of $T_N$ is higher in $x=0.4$ than in $x=0.3$, suggesting a S-induced magnetic order in the FeSe$_{1-x}$S$_x$ thin films. For slightly S-substituted $x=0.1$ with the nematic state, on the other hand, it was found that a long-range magnetic order was formed at low temperatures. As the value of $T_N$ at $x=0.1$ is higher than that of $x=0.4$, distinct magnetic states would be formed in the slightly (with nematic) and highly (without nematic) S-substituted FeSe$_{1-x}$S$_x$.
[1] F. Nabeshima et al., J. Phys. Soc. Jpn. 87, 073704 (2018).
[2] T. Terashima et al., J. Phys. Soc. Jpn. 84, 063701 (2015).
[3] F. Nabeshima et al., Phys. Rev. B 103, 184504 (2021).
