Size-dependent d0 room temperature ferromagnetism in undoped In2S3 nanoparticles

Abstract

Indium sulfide (In₂S₃) is a promising candidate material for spintronic applications. In this article, undoped In₂S₃ nanoparticles with varying sizes were fabricated via a gas–liquid phase chemical method and annealing process. The In₂S₃ nanoparticles with small particle sizes are subjected to annealing treatment in a nitrogen atmosphere for the purpose of adjusting the surface-to-volume ratio of the nanoparticles and avoiding magnetic doping. Magnetic measurements indicate that these nanoparticles clearly exhibit a room temperature ferromagnetic behavior, which decreases with increasing size due to annealing. Intrinsic defects are believed to be responsible for the observed ferromagnetism, which is fully elucidated in terms of the bound magnetic polarons (BMPs) mechanism. Notably, the defect-related d⁰ ferromagnetism of the samples can be conveniently modulated by controlling the particle size. First principles calculations reveal that the p–d exchange interaction between unpaired S 3p electrons induced by the In vacancies and In 4d electrons is the primary origin of ferromagnetism in In₂S₃. The size-dependent magnetic properties of pure In₂S₃ nanoparticles not only suggest potential applications in future spintronics and magneto-optics, but also propose a novel strategy for the exploration of pure diluted magnetic semiconductors (DMSs).