Microstructures And Magnetic Studies Of Co Doped Mg_xZn_1-xO Single Crystal Thin Films

For now, with the rapid development of technology, the information technology (IT) has been embodied in every aspect of people’s daily life. For the information technology, materials and devices are the key factors ensuring the development in the future. We all know that the microelectronic technology promoted the birth of the integrated circuit technology, and the integrated circuit technology is one of the basic conditions for the IT’s developing. Along with the progress of the integrated circuit technology, the size of the components was reduced, the integrated density increased rapidly, and the IT developed rapidly. But the size of the components could not be infinitely reduced, especially now when the size of the component was already close to the limit of the quantum coherence effect. Under this background, it is very important to find new materials, new devices and new technology. Electron has two degrees, charge and spin. The traditional microelectronic technology was based on the degree of charge, and people controlled the traditional electronic devices by the electric field to realize the data’s transmission, processing and storage. In this way, only the charge properties of the electron was used. So, if we can use the two properties of charge and spin, it will certainly improve the function of the devices and the development of information technology.Spintronics is a new discipline. The spintronics research the development of the spin electronic devices, which has important application value for the future development of science and technology. Later, the application of spin electronics to semiconductors has been studied. The spin polarized current was injected into the semiconductor, and new functions could be realized by the interaction between charge and spin. In this kind of devices, we can contron the spin of electrons or spin and charge at the same time in a semiconductor to realize data’s processing, transmission and storage. Compared to the traditional devices, the spin electronic devices have many of the advantages of:high speed; low power consumption -- energy consumption of spin interaction effect is far less than that of charge interaction; nonvolatile; compared with the full metal devices, spintronic devices, based on magnetic semiconductor, can realize the function of amplifying the signal, and can form a variety of equipment.We usually need four steps to realize the function of the spin electronic devices: spin injection, spin transport, spin detection and spin control. The first problem is spin injection. To realize the spin injection, people use the structure of ferromagnetic metal/ semiconductor, to inject the spin polarized current into the semiconductor from the ferromagnetic metal. But the large difference of the conductivity between ferromagnetic metal materials and semiconductor materials leads to the low efficiency of injection. Another way is to replace the ferromagnetic metal with magnetic semiconductors as spin injection source. Using magnetic semiconductors as an alternative material has many advantages. Firstly, the magnetic semiconductors have good electrical conductivity with the traditional semiconductor materials, which is good for improving the efficiency of spin injection. Secondly, magnetic semiconductors are close to the traditional microelectronic technology, which is good for the application of new materials. Suitable magnetic semiconductors need to meet some conditions:high Curie temperature (higher than room temperature), high saturation magnetization and so on. In order to achieve these conditions, people have made a lot of efforts to achieve room temperature ferromagnetic oxide magnetic semiconductors, which also stirred up people for the study of oxide magnetic semiconductors.The oxide ferromagnetic semiconductor has important research significance for the spintronic devices. There are still some difficulties for the people to overcome before the real application, such as the need for high saturation magnetization, and so on. MgxZn1-xO material system is a kind of very useful photoelectric functional materials. In addition, it also has other characteristics, such as large adjustable band gap range (3.4eV—7.8eV), the same combining power in this material for Mg and Zn and the carrier concentration significantly decreases with the increasing of Mg content. This makes that using Co doped MgxZn1-xO material system can help people to further study the mechanism of oxide magnetic semiconductor.In this paper, using the molecular beam epitaxy technology, we successfully prepared Co doped MgxZn1-xO single crystal thin film. We used the RHEED、XRD、 TEM to observe the structure and the morphology of this sample. And we used the AGM、SQUID and other technology to study the magnetism of this sample.The main content is below:(1) We prepared the Zn0.8S-xMgxCo0.15O (0≤x≤0.3) single crystal thin film, and analyzed its structure and morphology by using XRD and TEM, and verified the single crystal thin film in good condition. And according to the XRD data, we finally used the Bragg’s Law to introduce that Zn0.85-xMgxCo0.15O thin film share almost the same dependence between band gap and Mg content with the MgxZn1-xO thin film.(2) We prepared the fcc-Co0.5 (Mg0.55Zn0.45) 0.5O1-v single crystal thin film with high Co concentration. This thin film had high saturation magnetization strength, strong ferromagnetism at room temperature. By using structure characterization analysis and magnetic analysis, we put forward and finally verified the coexistence of ferromagnetic region, super-paramagnetic clusters and non-magnetic boundaries.(3) Through the experiments, we found a new efficient method for TEM sample preparation. Using this method, we can improving the success rate and efficiency, while keeping the condition of low pollution and low damage.