Research in the field of spintronics by Dr Aniekan Ukpong, Senior Lecturer in the School of Chemistry and Physics, is featured in the American Physical Society’s prestigious Physical Review B journal.
The article, titled Axial Field Induced Spin Response in Fe/hBN-Based Tunnel Junctions’, emanates from work done in the Theoretical and Computational Condensed Matter and Materials Physics (TCCMMP) research group established by Ukpong during the three years he has been at UKZN. It has to do with spintronics, the type of electronics that is based on the transport of electronic spin instead of charge.
‘We investigated using the spin of an electron and its magnetic moment as a means of performing computational activity, such as reading, writing and storing information,’ explained Ukpong.
Quantum electronic devices are used in the memory elements of drones, computers, cell phones, robots, aircrafts, satellites and more. Designing these devices to be energy-efficient, with larger storage capacity than is currently possible, and the ability to swiftly transfer data depends on the selection and combination of suitable metals. These metals are separated by an insulating barrier layer to ensure that electrons can only travel between the metal components by tunnelling through the potential barrier between the two electrically isolated metals. During the tunnelling event, electrons have their spins inverted and filtered so that only those spinning either up or down can get through, resulting in energy-efficient and fast-operating quantum devices.
The TCCMMP demonstrated how the external electric and magnetic fields generated when charge current flows into the scatter region of the tunnel junction can be used to tune or control the ability to store information in memory elements.
‘In tunnel junctions that contain iron as the pinned layer and monolayer hexagonal boron nitride (hBN) as the tunnel barrier, the use of cobalt, vanadium or nickel as the free layer allows for precise, atomic-level control of the information storing capacity,’ said Ukpong.
The research also revealed that at moderate to high electric fields, magnetisation, which determines the intrinsic ability of the device to store spin-based data, is reversed completely due to the emergence of an exotic electronic phase in the device.
Ukpong said that this work is important in the field of spintronics, particularly the sub-field of two-dimensional (2D) spintronics, because it demonstrates the distinct physical phenomena of the 2D elements used.
‘We showed that the monolayer hBN is versatile as the tunnel barrier layer in spintronic devices, and gained unique insights into what actually goes on at the electronic level, right inside spin-based memory elements, especially when they are subjected to varying amounts of charge current,’ said Ukpong.
He added that insights into the field-dependence of spintronic properties like the electric-field controlled perpendicular magnetic anisotropy of 2D magnetic tunnel junctions, which is key for preservation of data stored in the magnetic state of the information vector, are valuable for realising 2D spintronics. They are also useful in photovoltaic conversion device designs that are based on the tunnel junction architecture.
Ukpong, an NRF C3-rated researcher with more than 20 years’ experience in condensed matter and materials physics research, runs the research activities of the TCCMMP group under the Centre for High Performance Computing Research Programme, and is keen to explore the challenges of the computational implementation of the elements of modern physics students are learning. He is interested in seeing how research insights spur the development of new technologies in quantum devices, and how his group can utilise high-performance computations, operating with limited resources, to generate data to support international-quality scientific research that generates new knowledge in Condensed Matter and Materials Physics.
Postgraduate students linked to the TCCMMP are conducting research at UKZN, the University of Cape Town and the University of Johannesburg; the group is recruiting students with a passion for high-performance computing deployment in physics.
Words and photograph: Christine Cuénod