| dc.description.abstract | In the magnetoresistive random-access memory (MRAM) industry, spin-transfer torque (STT) based STT-MRAM has been proposed as a next-generation memory device because of its high-speed writing and reading processes and low energy consumption. However, the direct tunneling current passing through the device can reduce its lifetime due to Joule heating. On the other hand, the newly proposed spin-orbit torque (SOT) based SOT-MRAM may overcome this issue. Instead of a tunneling current, an in-plane writing current flowing through a heavy metal generates a SOT effect at the interface, rotating the magnetization direction of the magnetic free layer.
From a theoretical perspective, we aim to understand the mechanism of spin torques, considering material properties, magnetism, spin-orbit coupling (SOC), and electrical control. For this purpose, we developed the ＂JunPy＂ package to calculate STT and SOT using first-principles calculated self-consistent Hamiltonians with the nonequilibrium Green′s function (NEGF) method. This allows us to study both equilibrium and current-induced STT and SOT.
In this dissertation, we examine four systems to demonstrate spin torque calculations: (1) single-molecule magnetic junctions (SMMJs), (2) a conventional Fe/MgO/Fe magnetic tunnel junction (MTJ), (3) iron thin films, and (4) a novel van der Waals two-dimensional ferromagnetic (2DFM) heterojunction, Cr3Te4/PtTe2. Studying the equilibrium and current-induced STT in SMMJs and MTJs allows us to investigate the exchange bias effect and current-driven magnetization switching. The equilibrium SOT helps us exploring in-plane or perpendicular magnetic anisotropy beyond the energy method. Finally, we investigate the current-induced SOT and interfacial Rashba effect in Cr3Te4/PtTe2, demonstrating the potential for designing a room-temperature SOT-MRAM using 2DFM materials. These studies provide valuable insights into the mechanisms and control of spin torques, advancing the development of next-generation MRAM technology. Furthermore, our works highlight the potential of 2DFM materials in achieving efficient and reliable MRAM technology. | en_US |