Study On Spin Transport In Monocrystalline Cobalt Film And Polycrystalline Bismuth Thin Film

With the continuous upgrading of the electronic device, the size of device is reduced close to quantum scale where the quantum effect like electron tunneling can not be neglected. Due to the leak current of tunneling and the increasing heating effect in highly integrated electric circuit, the electron based device faces fundamental obstacles nowadays. To overcome these hindering, the spin of elec-tron, which has been long neglected in previous device development, has been considered to be a suitable candidate to replace electron in next generation elec-tronic device. The pure spin current costs only few percent of energy required by charge current to spread in conductor. A new research field in condensed matter physics has been developed and known as spintronics which aims at control and manipulation of spin. Realization of the inter-conversion of charge current and spin current is one of the central topic in the research of spintronics, because the spin current must be electrically detectable to be compatible with present integrated circuit device. The spin current can be converted into charge current in metal and semiconductor due to the existence of spin-orbit interaction by the band-relevant intrinsic mechanism or the scattering-relevant extrinsic mechanism. This conversion manifests in ferromagnetic material as anomalous Hall effect and in nonmagnetic material it appears as spin Hall effect. In my PHD thesis the anomalous Hall effect and spin Hall effect are studied in epitaxial cobalt film and polycrystal bismuth film respectively. The detailed content is as follows:1. fecc Co(001) thin film is grown by molecular beam epitaxial (MBE) method on. MgO(001) substrate. The residual resistivity is modulated by the film thickness and the scaling between anomalous Hall resistivity and longitu-dinal resistivity is studied. The anomalous Hall effect behavior in Co(001) film is similar to the case in Fe(001) studied previously and the intrinsic anomalous Hall conductivity is determined for the first time experimentally.2. The fcc Co(111) thin film is grown by MBE on MgO(111) substrate and transport measurement is carried out for samples with different thickness. The proper scaling discovered in Fe film and confirmed in Co(001) film is found to be valid only in the temperature range [5K,60K], while in higher temperature regime systematic deviation is detected. This deviation is more pronounced in the thinner film and increases with temperature. We suggests it may be due to the extrinsic mechanism driven by high-temperature excitation.3. The inverse spin Hall effect is studied in Bi/permalloy bilayer by spin pump-ing. The inverse spin Hall current in Bi is measured with various Bi thickness and a deceasing trend is found with increasing thickness which is not con-sistent with present theoretical model. We add an interface layer between the Bi and permalloy and work out the analytical expression of inverse spin Hall current in three-layer model and explain the experimental data quan-titatively. The spin Hall angle of the interface layer is-0.07and of opposite sign to the value in Bi volume.4. In the construction of experimental facilities, an ultra-high vacuum chamber with nine evaporation ports and two optical ports is designed and assembled. A matlab program is written to control the transport measurement in Oxford low temperature magnet system automatically.