Preparation and magnetic properties of chromium doped zinc sulfide and cadmium sulfide nanostructures by solvothermal method

Abstract

With the continuous development of nanotechnology, people have higher and higher requirements for the performances of nanomaterials. In the past few decades, researchers have used various methods to prepare nanomaterials with different dopants, and studied their optical and electrical properties. Nanomaterials with ferromagnetic properties have a wide range of applications, and there have been many reports about the ferromagnetic properties of doped magnetic elements. However, there have been few reports about Cr-doped ZnS and CdS. In order to obtain Cr-doped ZnS and CdS nanosheets with room temperature ferromagnetism, in this paper, using ethanolamine (EA) and ethylenediamine (EN) as mixed solvents, ZnS and CdS semiconductor nanostructures doped with different amounts of chromium are successfully prepared in S, ZnO and CdO sources by simple solvent thermal method. The X-ray diffraction (XRD) measurements show that the ZnS and CdS nanostructure have a wurtzite structure. Scanning electron microscopy (SEM) images show the morphologies of ZnS and CdS with different chromium content. When the content of Cr is 4.31 at% or 7.25 at%, the thickness of Cr-doped ZnS nanosheets is about 210–290 nm, and the morphology of undoped ZnS is composed of sub-morphologies of relatively thick nanosheets. The morphologies of CdS doped with different amounts of Cr are composed of sub-morphologies of snowflake like nanosheets with thickness of about 120–190 nm. Energy dispersive spectrometer (EDS) is used to observe the product composed of Cr, Zn, Cd, and S. The EDS measurement and calculation of the Cr content in Cr-doped ZnS nanosheets are 4.31 at% and 7.25 at% respectively, and those of the Cr content in Cr-doped CdS nanosheets are 1.84 at% and 2.12 at%. The vibration sample magnetometer(VSM) measurements show that ZnS doped with chromium exhibits ferromagnetism at room temperature, while the undoped ZnS exhibits diamagnetism at room temperature. The values of saturation magnetization <i>M</i>_s<italic/> of Cr-doped ZnS nanosheets with Cr = 4.31 at% and 7.25 at% are 2.314 and 5.683 (10^–3 emu/g), and the coercivity values of <i>H</i>_c<italic/> are 54.721 and 88.441 Oe, respectively. The ferromagnetism of pure CdS is weak, while that of Cr-doped CdS is enhanced at room temperature. The saturation magnetization <i>M</i>_s<italic/> values of Cr-doped CdS nanosheets with Cr = 0, 1.84 at% and 2.12 at% are 0.854, 2.351 and 7.525(10^–3 emu/g), respectively, and the coercivity values of <i>H</i>_c<italic/> are 74.631, 114.372 and 64.349 Oe, respectively. The values of saturation magnetization of ZnS and CdS increases with the Cr doping increasing. The ferromagnetism of Cr-doped ZnS at room temperature is confirmed by the experimental result, which is consistent with the ferromagnetism of Cr-doped ZnS calculated by the first principle. The origin of ferromagnetism of Cr-doped CdS is related to the doping of Cr in CdS lattice.