Tuning Paramagnetic effect of Co-Doped CdS diluted magnetic semiconductor quantum dots

Abstract

Diluted magnetic semiconductor quantum dots (DMS-QDs) are known for their outstanding optical and magnetic properties. II–VI DMS-QDs, in particular, are interesting for spintronics, nonvolatile memory, and magneto-optical devices. Therefore, studying the optical and magnetic properties of different II-VI semiconductors doped with transition metal atoms is of great importance. Tuning II-VI QDs optical properties can be mastered by changing the QDs particle size and/or structure. However tuning the magnetic properties of DMS-QDs is still within trial and error verification, although it is crucial in targeting different applications in spintronics. We hereby demonstrate, the ability to tune the paramagnetic effect of homogeneous Co-doped CdS QDs following a co-precipitation synthesis route with different Co2+ concentrations. The structural, optical and magnetic properties have been comprehensively studied. The dopant cobalt atoms concentration and chemical-configuration were precisely tracked by x-ray photoemission spectroscopy. Excitingly, the different Co-concentrations of 2, 5 and 10% significantly improve the magnetic properties of the CdS QDs, which exhibit a paramagnetic concentration-dependent effect. With 10% of Co atoms, we were able to achieve ~ 200 x 10(-6) molar susceptibility, that is, the same value to that of pure CoS. Thus we could obtain the highest possible paramagnetic effect in the CdS semiconducting matrix exhibiting 2.76 eV band gap, i.e. in the visible range. This efficacious result encourages the use of the present method in preparing DMS-QDs materials targeting various spintronics applications.