Control of spin injection by direct current in lateral spin valves

The spin injection and accumulation in metallic lateral spin valves with transparent interfaces is studied using d.c. injection current. Unlike a.c.-based techniques, this allows investigating the effects of the direction and magnitude of the injected current. We find that the spin accumulation is reversed by changing the direction of the injected current, whereas its magnitude does not change. The injection mechanism for both current directions is thus perfectly symmetric, leading to the same spin injection efficiency for both spin types. This result is accounted for by a spin-dependent diffusion model. Joule heating increases considerably the local temperature in the spin valves when high current densities are injected ($\sim$80--105 K for 1--2$\times10^{7}$A cm$^{-2}$), strongly affecting the spin accumulation.Comment: 6 pages, 5 figure

Spin transport in lateral spin valves and across a metal-insulator transition in V₂O₃

Spin valves is a class of spintronic devices that use spin degree of freedom. They have been used to study various condensed matter phenomena. Applications of the spin valves proved to be very useful in every-day electronics. Modern nano-fabrication techniques allowed further development of lateral spin valves. It was shown before that they separate spin and charge currents. These devices can provide a better insight into the spin transport and serve as a basis for the next generation of applications. In this thesis spin injection and detection in metallic lateral spin valves with transparent interfaces were studied using dc current. This allowed observation of two types of backgrounds present in the non-local spin valve signal. One of them originates from the inhomogeneous current distribution in the device. The other arises from the Joule heating. This heating was found to increase average temperature of the device by ̃100 K for the 10¹² A /m² current density. The magnitude of the non-local spin valve signal is symmetric with the current direction for current densities up to approximately 4x10¹¹ A/m². This indicates that the type of spin accumulation in the non- magnetic metal can be effectively controlled by the current direction. For higher current densities the signal becomes smaller when the current is injected from ferromagnetic electrode into the non-magnetic metal. This is explained by the spin-dependent Seebeck effect - an additional spin current is induced by a temperature gradient inside the ferromagnetic electrode. Non-local signal in copper/permalloy lateral spin-valves was measured as a function of distance between ferromagnetic electrodes, and Cu thickness. Extracted Cu spin diffusion length and permalloy spin-polarization decrease for smaller Cu thickness. This is explained by an additional spin-flip scattering at surfaces and interfaces of devices. Finally, Ni/V₂O₃/permalloy current-perpendicular- to-plane spin-valve devices were measured as a function of temperature. Unique geometry of the device allows observation of the metal-insulator transition in V₂O₃ at ̃160 K. Spin-valve effect was found in the device below the transition temperature. However the effect disappears at higher temperatures. Only anisotropic magnetoresistance of Ni was measured above ̃160 K. The observed magnitude of the spin valve effect, and its disappearance above the transition temperature, cannot be explained by simple 2- channel model for a device with transparent interfac

Spin transport in lateral spin valves and across a metal-insulator transition in V₂O₃

Spin valves is a class of spintronic devices that use spin degree of freedom. They have been used to study various condensed matter phenomena. Applications of the spin valves proved to be very useful in every-day electronics. Modern nano-fabrication techniques allowed further development of lateral spin valves. It was shown before that they separate spin and charge currents. These devices can provide a better insight into the spin transport and serve as a basis for the next generation of applications. In this thesis spin injection and detection in metallic lateral spin valves with transparent interfaces were studied using dc current. This allowed observation of two types of backgrounds present in the non-local spin valve signal. One of them originates from the inhomogeneous current distribution in the device. The other arises from the Joule heating. This heating was found to increase average temperature of the device by ̃100 K for the 10¹² A /m² current density. The magnitude of the non-local spin valve signal is symmetric with the current direction for current densities up to approximately 4x10¹¹ A/m². This indicates that the type of spin accumulation in the non- magnetic metal can be effectively controlled by the current direction. For higher current densities the signal becomes smaller when the current is injected from ferromagnetic electrode into the non-magnetic metal. This is explained by the spin-dependent Seebeck effect - an additional spin current is induced by a temperature gradient inside the ferromagnetic electrode. Non-local signal in copper/permalloy lateral spin-valves was measured as a function of distance between ferromagnetic electrodes, and Cu thickness. Extracted Cu spin diffusion length and permalloy spin-polarization decrease for smaller Cu thickness. This is explained by an additional spin-flip scattering at surfaces and interfaces of devices. Finally, Ni/V₂O₃/permalloy current-perpendicular- to-plane spin-valve devices were measured as a function of temperature. Unique geometry of the device allows observation of the metal-insulator transition in V₂O₃ at ̃160 K. Spin-valve effect was found in the device below the transition temperature. However the effect disappears at higher temperatures. Only anisotropic magnetoresistance of Ni was measured above ̃160 K. The observed magnitude of the spin valve effect, and its disappearance above the transition temperature, cannot be explained by simple 2- channel model for a device with transparent interfac