Public defence in Engineering Physics, M.Sc. (Tech) Maria Ameziane

Opponent: Professor Jordi Sort, Universitat Autònoma de Barcelona (UAB), Spain
Custos: Professor Sebastiaan van Dijken, Aalto University School of Science, Department of Applied Physics

The doctoral thesis is publicly displayed 10 days before the defence in the publication archive Aaltodoc of Aalto University

Electronic thesis

Public defence announcement:

Magnetic storage media continue to be widely used thanks to their high bit densities and long-term data storage capacity. To keep up with the increased demand for higher areal bit densities and fast device operation, electronic components have had to shrink in size. As the miniaturization trend continues, heat dissipation generated by electrons moving through circuits becomes significant. In addition to the penalty on power efficiency, smaller magnetic bits are also more susceptible to thermal fluctuations, which can jeopardize the integrity of the stored information. 

Addressing these roadblocks requires a paradigm shift in the design of hardware. Novel emerging forms of information processing, such as brain-inspired computing, additionally require functionalities not inherent to CMOS-based memory and logic. Much like the brain, they are designed to mimic the function of neural networks by combining the ability to efficiently process and solve complex tasks in parallel with low energy consumption. The nascent field of magnetoionics provides a promising alternative for the realization of next-generation low power magnetic memory technologies. Here, the state of magnetic “bits” is controlled through the voltage-induced motion of ions instead of lossy electronic currents. 

In this thesis, the voltage control of technologically relevant magnetic phenomena - more specifically perpendicular magnetic anisotropy, magnetic skyrmions and Ruderman-Kittel-Kasuya-Yosida interlayer coupling - was realized in miniature ionic devices inspired by solid-state lithium-ion batteries and supercapacitors. Lithium ions were used to control the properties of few-nanometer-thick magnetic multilayered thin films. The fabricated structures demonstrated deterministic and reversible modulation of the magnetic state with low voltages and good endurance under extensive operation. These devices also display functionalities suitable for nonconventional computing, including short-term plasticity and non-linearity of the magnetic response. These research outcomes represent a significant step towards the development of voltage-controlled magnetoionic elements that could act as building blocks for future brain-inspired applications for memory and logic.

Contact details of the doctoral student: [email protected]