Doctoral Defense in Physics - Mohammad H. Badarneh

Doctoral candidate:
Mohammad H. Badarneh

Title of thesis:
Energy-efficient control of magnetic states

Opponents:
Dr. Vitaliy Lomakin, Professor in the Department of Electrical and Computer Engineering, University of California, dr. Elton Santos, Professor at the Institute for Condensed Matter and Complex Systems, University of Edinburgh..

Advisor:
Dr. Pavel F. Bessarab, Associate Professor at Faculty of Natural Sciences, University of Iceland.

Also in the doctoral committee:
Dr. Hannes Jónsson, Professor at the Faculty of Physical Sciences, University of Iceland,dr. Cecilia Holmqvist, Associate professor at the department of Physics and Electrical Engineering, Linnaeus University, Unnar Bjarni Arnalds, Professor at the Faculty of Physical Sciences, University of Iceland.

Chair of Ceremony:
Dr. Birgir Hrafnkelsson, Professor at the Faculty of Physical Sciences, University of Iceland

Abstract:
Encoding data with magnetic states is currently used in various devices for data transmission, storage, and processing. The operating principle in these devices is often based on controlled switching, e.g., using a pulse of an external magnetic field, between stable magnetic states characterized by a certain direction of magnetization. However, for each act of magnetization change, a certain amount of energy is used. The challenge is to ensure that this operation is energy-efficient. In this thesis, we present the development and implementation of a theoretical framework for energy-efficient control of magnetization using an external magnetic field. The theory makes it possible to identify optimal control paths (OCPs) -- dynamical transition trajectories in the configuration space connecting the target states in the magnetic system and minimizing the energy cost -- from which all properties of optimal control pulses, including spatial and temporal distribution are systematically obtained without the need for an exhaustive scan over a range of amplitudes, frequencies or shapes. Therefore, the theory provides fundamental knowledge about the optimal manipulation of magnetization and solutions for low-power digital technologies based on magnetic materials. The theory is applied to the problem of energy-efficient control of magnetization switching in uniaxial and biaxial nanoparticles, as well as nanowires. For these systems, we show that following an OCP involves the rotation of magnetic moments in a manner that minimizes the impact of external stimuli while effectively harnessing the system's internal dynamics to facilitate the desired change in magnetization. Additionally, we show that the derived optimal switching protocols are robust with respect to thermal fluctuations in the technologically relevant regime and when the perturbation in the material parameters is not too large. Finally, we develop a method for enhancing the thermal stability of energy-efficient magnetization switching by applying an additional longitudinal magnetic field. The time-dependence of the stabilizing field can be obtained in a definite way by demanding bound dynamics of local perturbations induced by the thermal bath. The work presented in this thesis facilitates the development of energy-efficient information technology based on magnetic materials.

About the candidate:
Mohammad Badarneh, born in Jordan in 1992, holds both a bachelor's and master's degree in physics from Jordan University of Science and Technology, earned in 2015 and 2017, respectively. His doctoral research focused on developing and implementing a new theoretical framework for the energy-efficient control of magnetization transition using an external magnetic field. Beyond his scientific pursuits, he finds joy in various outdoor activities, including biking along the seashore, hiking in the mountains, bouldering, or engaging in a game of chess. After completing his Ph.D. degree, Mohammad will start his postdoctoral research at the University of Edinburgh.