Comparative Study of Room-Temperature Ferromagnetism in Undoped and Mn-Doped CdSe Quantum Dots

We report a comparative study of room-temperature ferromagnetism (RTFM) in undoped and Mn-doped CdSe quantum dots (QDs) synthesized by a pyrolysis method. Both undoped and Mn-doped CdSe QDs exhibited the RTFM with a coercive field of ~160 Oe. The magnetic moment of the QDs showed a strong dependence on the QD size, indicating that the RTFM of the QDs was due to an intrinsic effect. The saturation magnetization value of QDs increased with a decreasing of the QD size. Compared with the undoped QDs, the Mn-doped CdSe QDs exhibited the enhancement of saturation magnetization value with a slight doping concentration. By further increasing the Mn doping concentration to 4 at.%, the increase of the saturation magnetization value of the doped-QDs was not observed, which could be attributed to the enhancement of antiferromagnetic coupling between Mn²⁺ ions.