  Muon spin rotation/relaxation measurements were performed to investigate
magnetic properties of FeSe$_{1-x}$S$_x$ thin films on LaAlO$_3$. A drastic
decrease of the initial asymmetry was observed together with the peak structure
in the temperature dependence of the relaxation rate of muon spins almost at
the same temperature where kink anomalies were observed in the temperature
dependent resistivity. With increasing S content, the anomaly temperature
increased and the magnetic fluctuations at the lowest temperature were
suppressed. These results show that the S substitution induces magnetism at low
temperatures in FeSe$_{1-x}$S$_x$ thin films. Although the behaviors of the
magnetic and nematic phases in FeSe films towards chemical pressure by S
substitution are similar to those for bulk FeSe towards hydrostatic pressure,
the behavior of $T_{\mathrm c}$ is significantly different between these
systems. Our results demonstrate that the detailed comparative investigation
among physical and chemical pressure effects is essentially important to
understand the interplay of the magnetism, the nematicity and the
superconductivity in iron chalcogenides.
