Microstructure And Magnetic Properties Of SiC-based Diluted Magnetic Semiconductor Nanomaterials

Diluted magnetic semiconductors (DMSs) usually produced by doping semiconductors with transitionmetals have attracted considerable interest for spintronic devices where both spin and charge of electronsare utilized. As one of the most important DMSs, Silicon carbide (SiC) is a promising semiconductingmaterial because of its excellent physical properties, such as wide band gap, high electrical breakdown field,high thermal conductivity, which make SiC based DMSs a potential candidate in the area of high-power,high-frequency and high-temperature electronic devices. Diverse methods hve been reported for preparingDMSs and ferromagnetic ordering (FM) has been established at a wide temperature range, however, theorigin of the FM is still unclear.Recently, intensive research has been directed toward one-dimensional nanostructures and relateddevices. Preparation of spintronic devices from the bottom up might be feasible by adopting DMSsnanowires or nanotubes. Nanowires or nanotubes can avoid the effects of dislocations and the latticemismatch, offering thermodynamically stable features and typically single crystalline. Moreover,one-dimensional ferromagnetism nanowires can limit all spin rotations to a single axis, making thempotential candidates for spin transistors. So, nanowires or nanotubes have mang advantages over thin filmswith respect to studying magnetism in DMSs. To date, a great number of work about SiC based DMSs arefocused on the bulk materials or thin films. However, little work has been carried out to studymicrostructure and magnetic properties of transition metals doped SiC nanowires. In this work, transitionmetals doped SiC nanowires were prepared by controlling type and concentration of doped elementary.Microstructure and room temperature ferromagnetic ordering (RTFM) of SiC based DMSs wereinvestigated. The main content of this work is as follows:(1) Undoped and Mn doped3C-SiC nanoparticles were prepared by a sol-gel and carbothermalreduction method. The morphology of the nanoparticles was observed by scanning electron microscopy.The results demonstrated that the average particle size of the undoped and Mn doped SiC nanoparticles areabout60nm and200nm, respectively. Magnetic properties measurement showed that the Mn doped3C-SiC nanoparticles exhibited RTFM behavior and spin glass effect. (2) A simple method was used to synthesize undoped and Mn-doped3C-SiC nanowires underappropriate pressure, gas flowing and temperature. High purity Si, high purity SiO2, high purity manganesepowders and high purity graphite powders were used as starting materials. The phase and crystallinestructure analysis of the nanowires were examined by powder X-ray diffraction and Raman spectroscopy atroom temperature. Morphology and chemical composition were observed by scanning electron microscopyand energy dispersive spectroscopy attached to the scanning electron microscopy. Morphology andmicrostructure were observed by high resolution transmission electron microscopy. The magneticproperties were measured with a commercial superconducting quantum interference device magnetometer.The results demonstrated that the nanowires had single-crystalline Mn-doped cubic silicon carbide (3C-SiC)structure. The diameter of the nanowires ranged from30to200nm, with a length up to tens of micrometers.The high resolution transmission electron microscopy and selected area electron diffraction indicated thatthe nanowire grew along the [111] direction with the lattice spacing of0.254nm. The magnetic propertiesmeasurement showed that the nanowires exhibited RTFM behavior. We proposed that Mn doping alongwith the defects have great influence on local moment formation and collective magnetization. In addition,the FM may also originate from the existence of uncompensated spins and surface anisotropy since thenanowires have a very high surface-to-volume ratio.(3) Co-doped3C-SiC nanowires have been successfully synthesized. High purity SiO, high puritycarbon nanotubes, high purity cobalt powders and high purity graphite powders were used as startingmaterials. The phase structure, morphology, chemical composition and microstructure analysis of thenanowires were examined. The results demonstrated that the nanowires had single-crystalline Co-dopedcubic silicon carbide (3C-SiC) structure. The diameter of the nanowires ranged from20to150nm, with alength up to tens of micrometers. The high resolution transmission electron microscopy and selected areaelectron diffraction indicated that the nanowire grew along the [111] direction with the lattice spacing of0.253nm. The magnetic properties measurement showed that the nanowires exhibited ferromagnetic,paramagnetic and diamagnetic behaviors, dependent on the concentration of Co doping. The correlation ofCo content with magnetic properties is still need to be further investigated.