Abstract
There has been a great interest recently in novel magnetic devices such as magnetic patterned media, magnetic random access memory, and magnetic domain wall devices. However, with the scaling-down of the magnetic devices for the higher storage density, the degradation of thermal stability of the ferromagnetic layers with cell size becomes a severe issue for long-term storage and preservation. Therefore, the ferromagnetic materials with perpendicular magnetic anisotropy (PMA), which provides the better thermal stability due to the higher effective anisotropy, have been introduced to those novel magnetic devices for solving the thermal stability issue. Besides, PMA materials may also reduce the energy barrier for the spin-transfer-torque switching of the magnetic moments, leading to a more efficient reversal. Consequently, to integrate the PMA materials with those magnetic devices is a very important issue for pursuing better performance and smaller devices. The Co/Pt multilayers (MLs) is a kind of PMA materials, where its PMA is originated from the interfacial anisotropy of Co/Pt interfaces. Because the Co/Pt multilayers can be easily fabricated with tunable PMA, it has been widely applied to demonstrate the magnetic devices with PMA. Nevertheless, the magnetic properties of the Co/Pt multilayers are sensitive to the thermal process, which is hard to precise control the magnetic properties. Besides, due to the severe spin depolarization of Pt and the high damping constant, the Co/Pt multilayers is hardly reversed by spin-transfer torque, which limited the adoptability of Co/Pt MLs in real applications. In this work, we try to solve the problems of Co/Pt MLs in real applications. Two main directions have been focused: (1) precise control of the magnetic properties with the thermal process and (2) manipulation of the magnetization switching by electrical means. We first investigated the magnetic properties modification with rapid thermal annealing. We found the evolution of magnetic properties with thermal process is strongly correlated with the stress relaxation process. By controlling the stress relaxation in local regions, we can locally control the magnetic properties to achieve the so-called magnetic patterning. On the other hand, to find an electrical means for switching the Co/Pt multilayers, we evaluate the spin-orbit-torque efficiency of the Co/Pt multilayers. We found the spin-orbit-torque efficiency of the Co/Pt multilayers is strongly affected by the interface conditions and scaling with the repeating numbers of the multilayers. We also demonstrate the spin-orbit-torque switching on Co/Pt multilayers, where the multi-domain formation is a problem to obstruct the bipolar magnetization switching when repeating layer number is large. By engineering the interfaces, the multi-domain formation can be suppressed to achieve a completely switching with higher repeating layer numbers. As a result, our findings may improve the adoptability of Co/Pt multilayers in real applications.