Controllable Preparation And Magnetic Study Of Two-dimensional Magnetic Material CrTe

It is well known that ferromagnetic materials are one of the more important classes of magnetic materials with spontaneous magnetization and well-defined hysteresis behavior,and their physical properties can be manipulated using multiple degrees of freedom such as spin,orbit,charge and magnetic ordering,and have been widely used in various electronic devices.With the advancement of technology,Moore’s law requires devices to be miniaturized,and people have started to reduce the size of materials and thus the size of electronic devices.In recent years,various two-dimensional magnetic materials have been discovered.Two-dimensional magnetic materials with extremely thin thickness and unique electromagnetic properties are expected to be used in a new generation of spintronics devices.Currently,most of the 2D magnetic materials are prepared by mechanical stripping method,which cannot be processed into room temperature ferromagnetic devices because their thickness and size cannot be effectively controlled and the Curie temperature is far below room temperature.Therefore,the search for an efficient preparation method to synthesize 2D magnetic materials with relatively high Curie temperature has become the focus of research in this field.In this paper,we will use Chemical Vapor Deposition(CVD)to synthesize Chromium Telluride(CrTe),a non-layer transition metal-sulfur compound with high Curie temperature,and we will investigate the growth conditions,characterization of morphology and structure,and measurement of magnetic properties of CrTe nanosheets synthesized by CVD.The main works are as follows:(1)Synthesis of CrTe nanosheets.In combination with the growth conditions of chemical vapor deposition method,the size,growth rate,and growth quality of CrTe nanosheets were regulated by the controlled variable method by sequentially changing the pressure,substrate,temperature,and the mass of molten salt of the auxiliary agent.Finally,large size as well as high quality samples were obtained at low pressure(200 Pa),Si/SiO2 substrate,temperature of 750℃,and mass of NaCl of 3 mg.(2)Characterization of CrTe nanosheets.To obtain information on the surface morphology and thickness of the samples,we characterized the samples by optical microscopy,atomic force microscopy,and scanning electron microscopy,respectively.After that,we performed structural characterization of the samples.The single-crystal diffraction peaks and elemental valence states of CrTe nanosheets were characterized by X-ray energy dispersive spectroscopy,and finally the characteristic Raman peaks of CrTe nanosheets were identified by Raman spectroscopy.(3)Magnetic measurements of CrTe nanosheets.The M-T curves and hysteresis lines of CrTe nanosheets on Si/SiO2 substrates were measured by a superconducting quantum interferometer,and the average Curie temperature of CrTe nanosheets was obtained as 220 K.The variation of the coercivity field and saturation magnetization intensity with temperature was analyzed.Subsequently,the anomalous Hall effect was measured on CrTe nanosheets with a thickness of 85 nm by laser direct lithography,and the shape of the echelle was found to flip when the temperature was around 60 K.This phenomenon was analyzed.Finally,the magneto-optical Kerr effect was measured using the magneto-optical Kerr system for CrTe nanosheets with thicknesses of 23 nm and 156 nm,and the effect of thickness on the magnetic properties of CrTe nanosheets was analyzed.