Structural, optical and ferromagnetic properties of cobalt doped CdTe quantum dots

Cobalt doped cadmium telluride (CdTe) quantum dots (QDs) were synthesized with different Co concentrations by using non-aqueous method. Co_xCd_1−xTe QDs were characterized using optical absorption and photoluminescence spectroscopy, X-ray diffraction and high resolution transmission electron microscopy (HRTEM). It was noted that Co²⁺ was incorporated CdTe QDs without any shift in the diffraction peaks. HRTEM images revealed that the CdTe QDs were regular spherical particles with an average diameter of ~3 nm for undoped CdTe QDs and the average size of 2, 5 and 15 % Co²⁺ doped CdTe QDs were 4, 6.5 and 2.8 nm, respectively. Magnetization recognized for 0, 2, 5 and 15 % cobalt doped CdTe QDs revealed a ferromagnetic signal and ferromagnetic hysteresis loop. For pristine CdTe QDs a weak ferromagnetism was attributed to the charge transfer between capping agent and host CdTe QDs. Co²⁺ doped CdTe QDs exhibit stronger ferromagnetism and magnetic parameters such as saturation magnetization, M_S, remanence, M_R, and coercivity, H_C, of Co_xCd_1−xTe QDs were obtained from the hysteresis loops. It was found that with increasing the doping concentration of Co²⁺ in CdTe QDs up to 5 %, Ms increased.