Spin transfer torque effects and spin relaxation in magnetic nanostructures

Spintronics is an emerging field that the spin degree freedom of an electron is exploited as well as the electrical charge. The advanced lithography techniques enable the fabrication of the devices in the nanometer scale. The properties of spin transport in the magnetic nanostructures are interesting and attract more research attention recently.;The discovered spin transfer torque effects open the potential application of spin transfer torque magnetic random access memory. The Co/Cu/Co spin valves were fabricated, where the top Co layer is thinner than 0.5nm and only nanopartices are formed. The specialized point contact technique was utilized to conduct the experiments. Different contact resistances represent different contact diameter. The magnetization reversal of Co nanoparticles induced by spin transfer was inferred from the dV/dI-I measurements. The current density required for the switching is between 5x108 and 1x10 9 A/cm2 during the experiments.;Nonlocal spin valves (NLSVs) provide the ideal system to address the fundamental issues in the lateral transport. The NLSV structure generates a pure spin current and allows for the construction of multi-terminal devices. The success of spin injection is characterized by a substantial spin accumulation in the non-magnetic central entity. The figures of merit for achieving this goal are the spin polarization of the injected current ( P) and the spin diffusion length (lambdasf) in the non-magnetic entity. The ohmic-junction-based NLSV devices have been fabricated first during the course of this work. Then a thin layer of Al 2O3 is inserted between the magnetic electrode and the non-magnetic entity. The magnitude of the spin signals in the tunneling-junction-based NLSVs is much larger than the one in the ohmic-junctioned-based NLSVs. The values of P and lambdasf can be determined by a batch of devices with different separations. For the goal of spin transfer in the NLSVs, the d.c. bias is required. In our experiments, the high spin polarized at an elevated bias is demonstrated and no decreasing of spin signal is observed in the tunnel-junction-based NLSVs. The bias-dependence performance of the spin signals is attributed to the current redistribution effect. The temporal evolution of spin accumulation in NLSVs is also displayed and the increasing of the spin polarization and the spin diffusion length of the devices are discussed.