Abstract
This research work includes fabrication of high-quality free-layer magnetic materials with perpendicular magnetic anisotropy and generation of pure spin current in the magnetic multilayer structures for high-performance magnetic memory devices. In this dissertation, we study three different topics focusing on improving the material properties and developing new ways for device operation. The first topic focuses on improving the magnetic properties of ferromagnetic CoFeB. We studied its magnetic properties and modified the fabrication process to make it more suitable for device application. The way to manage the thermal budget of perpendicular-anisotropy CoFeB were also investigated. We found out that by adding an additional high-reactivity Al capping layer in Pd/CoFeB/MgO structure accompanying with rapid thermal annealing, we could fine-tune the interfacial Fe-O orbital hybridization as well as the amount of boron in bulk CoFeB, and optimize the magnetic properties of this structure. Eventually we developed one modified fabrication process that make CoFeB to possess low Gilbert damping constant and high thermal stability simultaneously. In the second topic, we tried to inject a pure spin current via microwave-induced spin-pumping in the Pd/CoFeB/MgO trilayer structure. Typically it is not allowed to have spin current injection in such perpendicular-anisotropy system via spin-pumping since the direction of angular momentum change during magnetization precession is parallel to the non-magnet/ferromagnet interface. However, by varying the orientation of applied field to break the symmetry of magnetization precession, we successfully injected a pure spin current into the non-magnetic Pd layer by spin-pumping, and we studied the relationship between the injected spin current and field orientation by using inverse spin Hall effect. We further investigated the roles of magnetic anisotropy and saturation moment on affecting spin-pumping. Finally we revealed the possibility to apply spin-pumping for spin current injection in such perpendicular-anisotropy devices operation. In the third topic, we passed a charge current through the high-spin-orbit-coupling Pd layer in the above mentioned trilayer structure and convert the charge current into pure spin current via spin-orbit interaction, and we found out that the pure spin current can also be injected into the nearby ferromagnet CoFeB layer and apply spin-transfer-torques to the magnetic moments of CoFeB. We analyzed the current induced effect field at two directions, in-plane parallel or perpendicular to the current, by lock-in vector measurement, and figured out the origins of spin-orbit coupling effects in this system. Finally, we demagnetized the out-of-plane magnetic moments by applying an in-plane current. This result proves that the pure spin current generated by high-spin-orbit-coupling materials has great potential on real device application, and the new operation mode can have huge opportunity to further improve the device performance in the near future.