Data storage technologies that utilize magnetic materials for storage are key for both increasing areal density of storage in traditional hard disk media and providing low energy alternatives to traditional CMOS technology through spintronic memory and logic devices. Spintronic memory relies on the spin of an electron rather than charge and is a promising candidate for achieving non-volatility which can provide dramatic energy savings. A key challenge for magnetic based storage is achieving 10 nm or smaller feature sizes while retaining thermal stability. This requires development of magnetic thin films with large magnetocrystalline anisotropy. Switching the magnetization of high anisotropy magnetic materials requires large Oersted field or spin current. One way to decrease the switching energy is to lower the anisotropy during the switching process with an applied strain or heat. This scheme retains thermal stability during storage and makes write energies feasible from a technological aspect. Development of suitable high anisotropy materials at sub 10 nm scale has proved difficult due to limitations on traditional thin film growth methods, nanoscale effects, and additional requirements on materials for memory applications. The effect of a static strain on the magnetic anisotropy is well understood, but less so for application in devices which require fast switching and high cycling. The other approach to lowering switching energies is to use magnetic materials with small magnetization, such as Mn-based compounds. I will discuss my experiments to advance understanding of: development of FePt for HAMR media, effect of strain assisted switching on the spin state of FePt, and development of novel high anisotropy Mn-based materials with low magnetization. Finally, I will present my experimental realization of Ru as the 4th room temperature ferromagnetic element. Ru has been predicted to become ferromagnetic when placed into a metastable tetragonal or cubic phase. This new phase of Ru also has potential to achieve the requirements for a viable spintronic device. I will show my work on the realization of the tetragonal phase Ru using seed layer engineering in thin films, and its associated ferromagnetic properties.
University of Minnesota Ph.D. dissertation. January 2018. Major: Electrical/Computer Engineering. Advisor: Jian-Ping Wang. 1 computer file (PDF); x, 122 pages.
High Anisotropy Magnetic Materials for Data Storage and Spintronic Memory.
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