| The electron has two degrees of freedom of charge and spin, which have been playing important roles in separated fields for a long time. The traditional microelectronics, which mainly studies and utilizes the transport properties of electron as a charge carrier, has become the cornerstone of modern information technology, while the traditional magnetics, which focuses on the electron spin property, occupy a central place in microwave communication and information storage. The newly-developed spintronics, however, studies the interaction between charge and spin of electrons in solids, and novel spintronic devices, which take advantage of both charge and spin, are expected as new generation devices by many scientists. The development of spintronics has its profound historical background. It is well known that the chip integration is becoming more and more dense while the size of the semiconductor devices shrink fast, which can be described by the Moore’s law. However, this high-speed development will soon meet the insuperable obstacle because the device size will enter nanoscale, in which the energy consumption per unit area will rise rapidly and result in serious heat damage problems and the quantum confinement effect rather than electron band theory will play a leading role. This challenging situation prompts the growing researches on revolutionized devices that are operated with totally different principle comparing with traditional microelectronic devices, with the anticipation of creating devices with faster arithmetic speed, smaller size and lower energy consumption. Along with the proposal of many prototype devices based on electron spin property, spintronics has become one of the hottest research area. To realize the goals of spintronics, the foremost mission is to develop a new material or structure, in which the charged electron motion is strongly coupled to the electron spin moment. The diluted magnetic semiconductor that possesses both room temperature ferromagnetism and spin-polarized carriers is the very material that meets all the requirements.The preparation method of a typical diluted ferromagnetic semiconductor was to dope transition element into the current used semiconductor system. It is expected that the transition elements may enter the crystal lattice by substituting some cation’s positions, and through ferromagnetic coupling between localized transition metal ions and itinerant carriers, ferromagnetism and spin-polarized carrier may appear in semiconductors. Mn doped GaAs prepared by low temperature molecular beam epitaxy method is one of the most matured diluted ferromagnetic semiconductor systems. This GaAs based diluted ferromagnetic semiconductor has provided the playground to demonstrate the feasibility of spintronic prototype devices proposed by scientists from all around the world. However, the Curie temperature, can only reach as high as200K, which does not meet the requirements of room temperature application. In order to obtain material that has room temperature ferromagnetism, researchers turn to study other semiconductor based diluted ferromagnetic semiconductor, which includes oxides, nitrides and IV group semiconductors, such as ZnO, TiO2, GaN, Si, Ge and so on. However, results reported by different groups are different or even contradictory. This implies a gloomy future for those diluted magnetic semiconductors to be used in spintronic devices. Over the last several decades, researchers have been attempted to increase the doping level of transition elements in traditional semiconductors by different unequilibrium growth method in order to increase the Curie temperature and saturated magnetization of the material, however, the low solubility of transition metal elements in semiconductor lattice, has limited the further increases of the institutional doping level.Given this research background, our group attempted to break the limitation of semiconductor lattice and turned to the exploration of disordered condensed magnetic semiconductors by using the creative thin film growth method that alternatively deposit an atomic-thin layer of semiconductor and an atomic-thin layer of transition metal elements. Our previous research results suggested that, this condensed magnetic semiconductors prepared by the nonequilibrium growth method has room temperature ferromagnetism and has promising future in room temperature spintronic devices. However, as our knowledge of disorder condensed magnetic semiconductors increases, some important questions emerges. For example, we did not observe anomalous Hall effects in previous room temperature magnetic oxides. Secondly, although the disordered condensed magnetic semiconductor has huge difference with ferromagnetic metal and semiconductor granular films, which implied the ferromagnetic origination is unlikely to come from the ferromagnetic metal clusters, however, we have not yet give the direct experimental prove to the ferromagnetic origination of the material. Those are also the questions that we attempted to solve in this work.(1) In this work, we improved the material growth method and introduce oxygen into the sample preparation chamber to control the properties of the condensed magnetic oxides. We finally chose In2O3as the material and prepared a series of In1-xCoxO magnetic semiconductor with same In and Co composition but different carrier densities.(2) All the samples have room temperature ferromagnetism while their saturated ferromagnetization decreased as the oxygen pressure increased, and at the same time, their resistivity increases.(3) The graze incident X-ray diffraction results indicated that, the sample with strongest ferromagnetism and most carrier concentration is amorphous, while oxygen induced a crystal phase in the sample that has no ferromagnetization. The high resolution transmission electron microscopy also confirmed the influence of the oxygen to the sample structure as mentioned above and indicated the cobalt and indium elements distribute homogeneously in the sample. The X-ray diffraction data has built direct connection between the ferromagnetism and the amorphous phase in the sample.(4) Furthermore, soft X-ray absorption spectra show that the introduction of oxygen also give rise to a new cobalt L-edge absorption feature, which shows no ferromagnetism as confirmed by soft X-ray magnetic dichroism spectra. Moreover, the soft X-ray magnetic dichroism results also show the magnetic properties of the sample is different from cobalt metal.(1) The series of disordered condensed magnetic semiconductors experience metal-insulator transition and the samples that is far way from the transition point show variable range hopping conduction at low temperature. This offers a good playground for many important physical research, such as anomalous Hall effect in variable range hoping.(2) We reported firstly the experimental observation of sign change of anomalous Hall resistivity in variable range hopping. We also observed that the scaling relationship between the anomalous Hall resistiviy and the longitudinal resistiviy disagrees with the existed theoretical prediction. According to our experimental results, we pointed out that the spin-orbital coupling of electrons in the variable range hopping region changes as temperature varies, which however has been considered as a constant in previous theory. As a result, our experiment is of significant importance for a better understanding of anomalous Hall effects in the variable range hopping.At last, we also studied the radiation damage effects and size-dependent core exition of two diamondoid isomers,[121] and [123] tetramantane molecules. The soft X-ray absorption results show the binding energy of the surface exciton that observed in tetramantane diamondoid is almost one order larger than that in the bulk diamond. We also found this core exciton state is very sensitive to the soft X-ray irradiation and [121] and [123] tetramantane showed different radiation damage effects. A two step model was introduced to explain those radiation related photochemical reactions. |
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