Abstract
In targeting reduced valent lanthanide chalcogenides, we report the first nanoparticle synthesis of the mixed-valent ferromagnets Eu(3) S(4) and EuSm(2) S(4) . Using divalent lanthanide halides with bis(trimethylsilyl)sulfide and oleylamine, we prepared nanoparticles of EuS, Eu(3) S(4) , EuSm(2) S(4) , SmS(1.9) , and Sm(3) S(4) . All nanoparticle phases were identified using powder X-ray diffraction, transmission electron microscopy was used to confirm morphology and nanoparticle size, and magnetic susceptibility measurements for determining the ordering temperatures and valence. The UV/Vis, Raman and X-ray photoelectron spectroscopies for each phase were compared. Surprisingly, the phase is influenced by the halide and the reaction temperature, where EuCl(2) formed EuS while EuI(2) formed Eu(3) S(4) , highlighting the role of kinetics in phase stabilization. Interestingly, at lower temperatures EuI(2) initially forms EuS, and converts over time to Eu(3) S(4) .