SPIN ORBIT TORQUE DRIVEN MAGNETIC SWITCHING IN THREE TERMINAL MAGNETIC TUNNEL JUNCTIONS
As the world has growing needs for storage of information, searching for the new generation memory technology that is non-volatile, energy efficient, and can be compatible with silicon technology is one of the popular topics of academic as well as industrial research. In this dissertation I present experimental work on various spin-orbit-torque driven switching behaviors and possible application of these phenomena. I show that with novel methods of material optimization and structural modification, three terminal magnetic tunnel junctions with in-plane anisotropy can rise up to the front of this search and can possibly change the memory writing scheme in the future. From the beginning of this century, spintronics has gained much attention due to its rich and intriguing physics. The possibility of manipulating magnetization locally through angular momentum exchange by the spin orbit coupling also advances the magnetic storage technology from field-driven to current-driven switching, which significantly enhances the compatibility and scalability of these elements. After the introduction in Chapter 1, I show some switching experiments on micron-sized Hall bar structures with perpendicular magnetic anisotropy (PMA) in Chapter 2. I discuss the significance of various works on PMA structures and the popularity of future direction of the research. In Chapter 3 and 4 I describe the nano-fabrication procedures and novel measurement techniques that I built and used to obtain the switching results that will be introduced in the subsequent chapters. In Chapter 5 I show an effective way of reducing write current in three terminal magnetic tunnel junctions (MTJs) using sub-atomic Hf dusting layers and explore the various properties of this technique. In Chapter 6 and 7 I mainly focus on fast, nanosecond pulse switching of MTJ devices based on the Pt85Hf15 alloy spin Hall channel. I present some novel ways of manipulating spin torque switching dynamics and how we can obtain enhanced switching behavior with the modification of device geometries. Finally in Chapter 8 I briefly touch on the set-up of a high frequency low temperature cryostat and some interesting and yet-to-be-understood phenomena of spin-torque switching in the low temperature regime where the amplitude of thermal fluctuations is low.
Applied physics; Spintronics; Physics; MRAM; magnetic tunnel junction; Nanotechnology
Buhrman, Robert A.
Kim, Eun-Ah; Fuchs, Gregory David
Doctor of Philosophy
dissertation or thesis