Cobalt-induced Multifunctionality: Ferromagnetism and tunable optoelectronic properties in hydrothermally synthesized SnS2 nanoparticles

Abstract

Research into Diluted Magnetic Semiconductors (DMS) has experienced significant advancement over the past decade. This progress is largely attributable to the development of sophisticated synthesis techniques, which have enabled the fabrication of high-quality samples with well-characterized properties for experimental study. Consequently, DMS are widely regarded as a leading material platform for the development of spintronic devices. This study comprehensively investigates the first-principles study of SnS₂ and structural, morphological, chemical, optical, and magnetic properties of hydrothermally prepared pure and Cobalt-doped SnS₂ (1 %, 3 %, 5 %, 7 %) nanoparticles. X-ray diffraction analysis confirms the preservation of the hexagonal crystal phase post-doping. In contrast, Williamson-Hall (W-H) plot analysis indicates an increase in crystallite size from 32.9 nm to 66.8 nm with Co concentration. FESEM reveals a nanoflower-like morphology. X-ray photoelectron spectroscopy verifies the presence of Sn⁴⁺ and S²⁻ states and confirms the successful incorporation of Co dopants, which exhibit mixed Co²⁺/Co³⁺ oxidation states. Optical characterization demonstrates a reduction in reflectance and a narrowing of the optical band gap from 2.26 eV to 1.56 eV with doping. Density functional theory shows that the band gap of pure SnS₂ is direct. The Urbach energy, initially increasing up to 3 % Co doping, suggests a rise in structural disorder, followed by a subsequent decrease. A reduction in the refractive index from 4.62 to 3.10 indicates enhanced optical transmission, while a increase in optical and decrease in electrical conductivity is observed. The tunability of the emission wavelength across the visible spectrum, as observed in the photoluminescence (PL) spectra, is directly enabled by Co-doping. This controllability underscores the material's strong potential for application in advanced optoelectronic devices. Furthermore, the observed hysteresis loop confirms the emergence of ferromagnetic ordering upon cobalt doping. These findings collectively demonstrate that Cobalt-doped SnS₂ is a promising diluted magnetic semiconductor (DMS) material, whose tunable properties make it a strong candidate for application in spintronics and multifunctional optoelectronic devices.