Super Exchange-Induced Canted Ferromagnetism in Transition Metal-Doped ZnS Quantum Dots

ZnS quantum dots doped with magnetic transition metal (Zn1-x TM (x) S; where x = 0.04, 0.08 and transition metal = Ni, Mn, Fe, Co and Cr) were synthesized using a chemical co-precipitation method. To prevent agglomeration, samples were capped with polyvinylpyrrolidone. X-ray diffraction peaks confirmed pure cubic phases of all samples. The crystallite dimensions of the samples are within the scale of 2.0-2.6 nm, which was calculated using Scherrer formula. A band gap varying from 4.1 eV to 4.24 eV was estimated from their ultraviolet-visible absorption spectroscopy. The synthesized samples show a strong blue shift in their emission spectroscopy along with emissions from inherent Zn and S point defects (interstitial and vacancy). Superconducting quantum interference device studies at 300 K reveal that all samples show room temperature canted ferromagnetism at low magnetic fields which does not saturate even up to a fields of 5 T. We study the defects as seen through emission spectroscopy and correlate with the magnetic properties of the doped semiconducting quantum dots.