Strong enhancement of magnetic critical temperature followed by loss of magnetism in EuPd₃S₄ under high pressure

This work presents a comprehensive high-pressure study of the mixed-valent compound EuPd₃S₄ by electrical transport measurement, ¹⁵¹Eu synchrotron Mössbauer spectroscopy, X-ray absorption spectroscopy, and high-resolution X-ray diffraction. We find that the antiferromagnetic ordering temperature is strongly enhanced from 3 K to 25 K as the pressure is increased to 28 GPa. Above 28 GPa, a clear 1^st order Eu²⁺ to Eu³⁺ valence transition is observed alongside 1) the vanishing of the magnetic order and 2) a cubic to tetragonal structural phase transition. These rich results suggest that the magnetic ordering temperature is enhanced as 4f hybridization with the conduction band is increased up to a critical value beyond which a sudden valence/ structural transition takes place. As such EuPd₃S₄ appears to be an excellent system for the detailed study of how magnetism, valence and structure are intertwined and should serve as a benchmark for theoretical efforts to model and understand mixed valence behavior.