Synthesis, Formation Mechanism, and Magnetic Properties of Monodisperse Semiconducting Spinel CdCr₂S₄ Nanocrystals via a Facile "seed-Mediated" Growth Method

The chalcogenide spinel CdCr₂S₄ is a well-established ferromagnetic semiconductor that exhibits unique properties and is a promising candidate for spintronic applications. With band gap in the visible wavelength region, CdCr₂S₄ nanocrystals offer the exciting possibility of tailoring both the optical and magnetic properties with precise morphology control. However, the synthesis of monodisperse CdCr₂S₄ nanocrystals is challenging and has not been reported. A unique "seed-mediated" growth process has been developed for the synthesis that involves using cubic-phase CdS, which has a face-centered cubic crystal structure similar to that of CdCr₂S₄, as a "seed" to react with CrCl₃·6H₂O in a solution mixture of 1-dodecanethiol and 1-octadecene. Remarkably, hexagonal-phase CdS is ineffective as a "seed" for formation of the desired product. A mechanism for formation of monodisperse CdCr₂S₄ nanocrystals by the selective growth process is proposed, and the structural and magnetic properties of the synthesized nanocrystals are presented. The novel synthetic strategy can be exploited for the controlled formation of other complex magnetic chalcogenides.