The interplay between magnetism and structure in Co/Fe-CdSe diluted magnetic quantum dots†

Magnetic dopants are commonly employed to modify the characteristics of dilute magnetic quantum dots (DMQDs), resulting in a significant alteration in their magnetic ground state. A thorough investigation of the structural changes induced by the dopants during DMQD growth is pivotal to comprehending the magnetic state of the system. In this regard, we employed the well-established organometallic route to manufacture CdSe QDs with trace amounts of Co and Fe, and we halted their growth process at two different stages. Subsequently, we utilized high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence, and vibrating sample magnetometry to examine the interplay between each structure and its magnetic properties. Our analyses reveal that Co ions form a β-Co(OH)₂ shell on the surface of the CdSe QD, changing the diamagnetism of the pure CdSe matrix into soft-ferromagnetism of the DMQD at a low magnetic field, accompanied by a substantial enhancement in photoluminescence, amounting to approximately 250% in comparison to the pure CdSe QDs. In contrast, Fe ions form a FeSe structure in the core of the CdSe QD, leading to a room-temperature ferromagnetic DMQD. Both DMQDs are potential candidates for quantum information storage and processing, enabling the development of advanced quantum technologies.