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The discovery that a metal most commonly found in meteorites possesses a link between its crystalline structure and its magnetic properties could be a boon for spintronic technology.
Researchers have discovered that instabilities in a material’s crystalline structure that switch it from an insulator to a conductor can be controlled by magnetizing it. In a paper, published in the journal Nature Physics, a team of material scientists from Duke University describes how the exploration of the physical properties of rare metal, hexagonal iron sulfide or troilite, could be key to unlocking the potential of spintronics. Itself a major step towards the implementation of quantum computing.
Troilite — a material that is scarce on Earth, but is common in meteorites and asteroids — exhibits a coexistence of metal-insulator with structural and magnetic transactions arising from the interplay of its quantum qualities such as its ‘spin’ — which is not related to angular momentum, but better described as a magnetic phenomenon.
Recent developments in the study of this ‘space metal’ suggest that there are extraordinary physics at play when troilite is heated to between 143 ⁰C and 317 ⁰C. In this temperature range, troilite ceases to be magnetic and becomes an isolator.
The team’s research suggests that the material’s properties are caused by a shift in the atoms within its crystalline structure. The vital part of this complex interaction, observed for the first time by material scientists, is the interaction between the material’s magnetic and electrical properties and its atomic dynamics — a new realm of study that could be of vital importance in the future of computing.
Tuning in to Troilite
The idea of ‘tuning’ a material’s magnetic state via the application of electric current could be of significant use in the realization of spintronic computing. Spintronics involves the use of an electron’s spin and magnetic moment to store data.
And make no mistake, spintronics is big business.
According to a Research and Markets report in late 2018, the global spintronics market is expected to reach a value of over 17.6 billion USD by the year 2023. In another example of how important spintronics is in the development of future computers, in January this year, Dr. Wei Zhang, an assistant professor of physics at Oakland University. was granted half a million USD to conduct a five-year research program
The importance of spintronics is reflected by the number of companies currently heavily involved in this relatively new field of research. Arguably, foremost amongst these is IBM, which formed in 1903 and has gone on to become a household name in computing. IBM researches spintronics in conjunction with Stanford University and through the co-founded SpinAps — IBM-Stanford Spintronic Science and Applications Center.
The SpinAps research center is manned by a dozen Stanford professors and IBM scientists assisted by ten or so graduate students who, like scientists working at other spintronic based-facilities, are probably very interested in researching troilite, which could potentially become quantum computing’s equivalent to silicon.
Instabilities, Magnetism, and Conductivity
The Duke University team took samples of troilite crystals grown by the University of Tennessee to Oak Ridge National Laboratory so that they could be bombarded with neutrons and to Argonne National Labs where they could be exposed to X-ray photons. The interaction with these different particles allowed the researchers to investigate distinct but related properties of troilite.
When neutrons collide with the atoms in the material’s crystalline structure their refraction allows the researchers to measure the direction of each atom’s magnetic spin. As neutrons interact weakly with these atoms, the X-rays allow the physicists to resolve troilite’s atomic structure and the atomic vibrations in the crystalline structure that comprises it.
The team then brought these separate results together for comparison and analysis with quantum mechanical models by the supercomputer based at Lawrence Berkeley National Laboratory. Their analysis of the changes occurring during the material’s phase transition revealed mechanisms at work that were, as of yet, undiscovered.
When troilite reaches high temperatures the magnetic spins of its atoms cease to be well-ordered and arrange so that their magnetic moments are pointing in random directions. The significance of this change is that it means that the material is no-longer magnetic. This change is reversible, as the temperature drops again the atoms realign and the material once again becomes magnetic.
These magnetic shifts have a wider significance, as the alignment of the material’s magnetic spin alters its vibrational dynamics. This shift causes the crystalline structure to deform and this, in turn, creates a bandgap that hinders the flow of electrons. In short, the material loses the ability to conduct electricity.
This represents the first time that researchers have conclusively witnessed the control of instabilities of a material’s crystalline structure via the manipulation of its magnetic spin. In turn, it reveals that certain materials’ instabilities connect their magnetic and conductive potential.
The manipulation of these qualities currently requires the use of temperature change, which is perhaps not viable as a control mechanism because quantum computers require cool-conditions and strict environmental isolation to prevent the disturbance of entangled states and in-turn, information loss.
The team behind this paper is therefore keen to find another ‘handle’ by which these qualities can be adjusted. This could involve the application of external magnetic fields and the observation of how these affect troilite’s atomic and crystalline dynamics.
In addition to this, the fact that troilite, though rare, has been studied very thoroughly without a hint at these mechanisms implies that there may be other well-known materials that hide properties such as this. Perhaps some of these materials could even be more common and widely available than troilite.
References and Further Reading
Bansal. D, Niedziela. J. L, Calder. S, et al., (2020) Magnetically-Driven Phonon Instability Enables the Metal-Insulator Transition in h-FeS. Nature Physics, [DOI: 10.1038/s41567–020–0857–1]
‘Global $17+ Billion Spintronics Market by Type of Device, Application and Region — Forecast to 2023,’ Research and Markets (2018).