‘Multiferroic materials have potential to revolutionise data storage capacity’

3 Feb 2021

Dr Lynette Keeney, senior researcher at Tyndall National Institute. Image: Clare Keogh

Dr Lynette Keeney at Tyndall National Institute is leading research into groundbreaking materials that are bringing us closer to next-generation data storage.

In 2015 and again in 2020, Dr Lynette Keeney was awarded prestigious University Research Fellowship Awards from the Royal Society and Science Foundation Ireland (SFI) for her research project, ‘Memories are made of this’.

Memory, in Keeney’s research, is made of multiferroics. These are materials that exhibit multiple primary ferroic properties in the same phase. These properties include ferromagnetism (magnetisation that is switchable by an applied magnetic field), ferroelectricity (electric polarisation that is switchable by an applied electric field) and ferroelasticity (a deformation that is switchable by an applied stress).

For Keeney, the focus is on the combined properties of magnetism and electric polarisation, because of the possible applications in data storage. These materials are rare, but in 2013, Keeney made a research breakthrough by developing a multiferroic material that operates at room temperature.

Her materials science career began at Tyndall National Institute in University College Cork, where she made this breakthrough. She then began developing her own independent research programme and team, which she is now expanding thanks to the renewal of her fellowship and an SFI Frontiers for the Future research grant of more than €400,000 awarded late last year.

‘The remarkable growth of the internet means that data storage based on either electric or magnetic information storage is already struggling to match the ever-increasing demand for data’

What inspired you to become a researcher?

I am told that as a child, I was always asking questions. Why? What? Where? How? This was encouraged by my parents and I loved activities where I could learn what things are made up of, how things work or why things work as they do.

A few years ago, in my parent’s attic, I found a copybook project that my mum and I did together when I was very small. Within the copybook, we inserted flowers that we had picked from the garden, labelled the parts and described how flowers make seeds.

I recall that as a child I was curious to learn about static electricity, being confused at first and feeling the need to understand. As children, my sister and I got a microscope as a present and we loved looking at insect wings, cheek cells, strands of hair etc up close.

As a researcher now, I love to apply the understandings of what I have learned to drive new discoveries.

What research are you currently working on?

Using my chemistry background, I design, characterise and optimise the physical properties of new materials at nanoscale with the target of implementing these new materials in future data storage devices.

While current computer memories use either electric or magnetic polarisation to store information separately in single-bit devices, I develop new multiferroic materials which can simultaneously combine ferroelectric and ferromagnetic storage for multi-bit devices. Data storage technologies based on multiferroic materials are expected to permit a fourfold or higher increase in the amount of information that can be stored.

In an exciting new SFI Frontiers for the Future project with co-principal investigator Dr Michael Nolan, we are fostering a new collaboration between theory and experiment to enhance the functional properties of this revolutionary multiferroic material. Here we are exploring how even subtle differences between the ways that atoms arrange within the structure can have a marked influence on the material’s fascinating physical properties.

In your opinion, why is your research important?

We need research to collect facts, reach conclusions, enable creativity, lead to new discoveries and ultimately progress our lives. Without research there would be no advances – and no much-needed vaccines, as a topical example!

What commercial applications do you foresee for your research?

The remarkable growth of the internet means that data storage based on either electric or magnetic information storage is already struggling to match the ever-increasing demand for data. Multiferroic materials simultaneously combine electric and magnetic information states, with the unique commercial potential to enable a fourfold or even eightfold increase in the amount of data that we can store. Furthermore, coupling between the ferroelectric and ferromagnetic information states permits energy-efficient electrical switching of magnetic memory states.

Developing materials for neuromorphic, or brain-inspired, computing applications is another particularly exciting direction, and we are targeting this within Tyndall’s CMOS++ strategic research cluster.

What are some of the biggest challenges you face as a researcher in your field?

Multiferroic materials have potential to revolutionise data storage capacity, but there are as yet no such devices that can realise this promise. This is because multiferroics which work at room temperatures are not only extremely rare, but also remain to be proven to work at the sub-10nm thicknesses required for nano-electronics. This is about 8,000 times thinner than a human hair, to put it into perspective.

Although this is recognised by the multiferroics community as a challenging task, our recently published paper describes how switchable ferroelectric polarisation persists in 7nm thick samples at room temperature and demonstrates the recent progress we have made in the optimisation of our multiferroic material towards accomplishing this goal.

Are there any common misconceptions about this area of research?

While there are several reports of samples that exhibit ferroelectric and ferromagnetic responses at room temperature, over the course of my research I have learned that it is important to carry out rigorous analysis of sample purity before one can be confident that a material is truly a single-phase multiferroic. My publications stress that secondary phase magnetic impurities, even when present at minute volumes undetectable by conventional techniques such as x-ray diffraction, can in fact be responsible for observed ferromagnetic signals, rather than the main sample itself.

Based on the need to scrutinise phase purity, at Tyndall we developed an approach to investigate candidate multiferroic samples using nanoscale chemical mapping and electron microscopy combined with rigorous statistical analysis. This allowed us to establish genuine multiferroicity with a confidence level of more than or equal to 99.5pc. This type of detailed analysis has since informed subsequent studies on necessary analysis measures to take.

What are some of the areas of research you’d like to see tackled in the years ahead?

Specifically in my research field, I find the role that defects have on influencing physical properties to be fascinating and I think that this will be probed further as advancements in microscopy allow.

Interestingly, in my material, defects can increase the probability of magnetic atom alignment, thereby increasing magnetic response. We have also learned recently that accumulation of charged defects supports domain wall conduction, which is of complete contrast to the insulating ferroelectric bulk material. Since charged domain walls can be created, destroyed or moved at will by applying simple voltage pulses, they are an emerging research focus in nano-electronics and domain wall devices.

Defects also facilitate the formation of exotic polar vortices, exhibiting a continuous rotation of the local polarisation vector. Not only are these vortices visually spectacular, polar vortices are associated with exotic properties such as negative capacitance, which can reduce the voltage requirements of a transistor, thereby enabling more energy-efficient electronic devices.

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