Sulfur-induced magnetism in iron-chalcogenide thin films

Magnetic properties of Fe(Se,S) thin films on LaAlO₃ were investigated via muon spin rotation/relaxation. 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 increases and the magnetic fluctuations at the lowest temperature was suppressed. These results show that the S substitution induces magnetism at low temperatures in Fe(Se,S) 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_c is significantly different between these systems. Our results suggest essential importance of the detailed comparative investigation among physical and chemical pressure effects for bulk and film samples to understand the interplay of the magnetism and the superconductivity in iron chalcogenides.