The Anomalous Hall Effect In Co And Co_xN Films

Anomalous Hall effect(AHE) as a basic tool to probe and characterization the transport properties of cruise electron in ferromagnetic materials, plays a very important role for the transport properties of spin electron in all the dilute magnetic semiconductors. In recent years, with the AHE Berry phase put forward, which make AHE become a hot topic once again in the study of condensed matter physics.The discovery of anomalous hall effect has been more than one hundred years. But its origin mechanism is still controversial. The focus of the controversy is whether the origin of AHE is band effect or scattering effect. In 1954, Karplus and Luttinger first proposed a theory for AHE and insisted that the origin of AHE was determined only by the energy band structure and spin-orbit interaction of material, but had nothing to do with defects and impurities. The extrinsic mechanism of Skew scattering and Side jump, which depended on the potential and the form of scattering, were later proposed by Smit(in 1955) and Berger(in 1971) respectively. As the development of Quantum Hall effect, the notion of Berry phase was introduced to account for AHE by researchers.Combine with the berry phase theory and first principles calculation, which make it possible to achieve quantitative study of AHE. Considering the band of material depends on the crystal structure and based on modifying phase structure of samples, we prepared Co thin films and Co-N thin films to discussing the AHE. Because of the rich phases of cobalt and nitrogen compounds, we analysed and distinguished their intrinsic and extrinsic of AHE. The method of combining phase structure and AHE provided us novel ideas. The main work is as follows:1.Using dc magnetron sputtering, we grew cobalt thin films on glass substrates. XRD result show that the phase structure of Co thin film strongly depends on the temperature of substrates. By changing the temperature of substrates, we prepared series cobalt thin films. The XRD shows that the samples including two phases, ε-Co and α-Co. The value of saturation magnetization increase with the improve of temperature, and longitudinal resistivity reduce from 351.4μΩ cm to 4.3 μΩ cm. For the sample of ε-Co, we found the AHE mainly from skew scattering mechanism.2. Co-N thin films were grown on glass substrates by DC magnetron sputtering. The substrate temperature was 270℃. The XRD showed that the samples of 0-4% N partial pressure were cubic structure, and the samples of 6-16% N partial pressure were hexagonal structure. The value of saturation magnetization rapidly reduced with the increase of nitrogen partial pressure, and longitudinal resistivity increased from 65.1 μΩ cm to 471.2μΩ cm. By contrasting the measuring results, we found that for the AHE of Co-N thin films, skew scattering mechanism plays a major role. And there are relatively weak intrinsic mechanism and side jump mechanism coexistence.