Tyler O'Neal, Staff Editor STORAGE

UK physicists unravel ‘Hall effect’ mystery in search for next gen storage

An advance in the use of antiferromagnetic materials in memory storage devices has been made by an international team of physicists.

Antiferromagnets are materials that have an internal magnetism caused by the spin of electrons, but almost no external magnetic field. They are of interest because of their potential for data storage since the absence of this external (or ‘long range’) magnetic field means the data units – bits – can be packed in more densely within the material.

This is in contrast to ferromagnets, used in standard magnetic memory devices. The bits in these devices do generate long-range magnetic fields, which prevent them from being packed too closely because otherwise, they would interact.

The property that is measured to read out an antiferromagnetic bit is called the Hall effect, which is a voltage that appears perpendicular to the applied current direction. If the spins in the antiferromagnet are all flipped, the Hall voltage changes sign. So one sign of the Hall voltage corresponds to a ‘1’, and the other sign to a ‘0’ – the basis of binary code used in all computing systems.

Although scientists have known about the Hall effect in ferromagnetic materials for a long time, the effect in antiferromagnets has only been recognized in the past decade or so and is still poorly understood.

A team of researchers at the University of Tokyo, in Japan, Cornell and Johns Hopkins Universities in the USA, and the University of Birmingham in the UK have suggested an explanation for the ‘Hall effect’ in a Weyl antiferromagnet (Mn3Sn), a material which has a particularly strong spontaneous Hall effect.

Their results have implications for both ferromagnets and antiferromagnets – and therefore for next-generation memory storage devices overall.

The researchers were interested in Mn3Sn because it is not a perfect antiferromagnet, but does have a weak external magnetic field. The team wanted to find out if this weak magnetic field was responsible for the Hall effect.

In their experiment, the team used a device invented by Doctor Clifford Hicks, at the University of Birmingham, who is also a co-author of the paper. The device can be used to apply tunable stress to the material being tested. By applying this stress to this Weyl antiferromagnet, the researchers observed that the residual external magnetic field increased.

If the magnetic field were driving the Hall effect, there would be a corresponding effect on the voltage across the material. The researchers showed that the voltage does not change substantially, proving that the magnetic field is not important. Instead, they concluded, that the arrangement of spinning electrons within the material is responsible for the Hall effect.

Clifford Hicks, a co-writer of the paper at the University of Birmingham, said: “These experiments prove that the Hall effect is caused by the quantum interactions between conduction electrons and their spins. The findings are important for understanding – and improving – magnetic memory technology.”

Illinois researchers propose the future of data storage is double-helical

Tyler O'Neal, Staff Editor STORAGE

Imagine Bach’s “Cello Suite No. 1” played on a strand of DNA. (From left) University of Illinois Urbana-Champaign researchers Charles Schroeder, Kasra Tabatabaei, and Chao Pan collaborated with researchers from UIUC, the University of Massachusetts at Amherst, and Stanford University to transform DNA into a robust, sustainable data storage platform fit for the Information Age and built to last well beyond the 21st century.

This scenario is not as impossible as it seems. Too small to withstand a rhythmic strum or sliding bowstring, DNA is a powerhouse for storing audio files and all kinds of other media.

“DNA is nature’s original data storage system. We can use it to store any kind of data: images, video, music — anything,” said Kasra Tabatabaei, a researcher at the Beckman Institute for Advanced Science and Technology and a co-author on this study.

Expanding DNA’s molecular makeup and developing a precise new sequencing method enabled a multi-institutional team to transform the double helix into a robust, sustainable data storage platform.

The team's paper appeared in Nano Letters in February 2022.

In the age of digital information, anyone brave enough to navigate the daily news feels the global archive growing heavier by the day. Increasingly, paper files are being digitized to save space and protect information from natural disasters.

From scientists to social media influencers, anyone with information to store stands to benefit from a secure, sustainable data lockbox — and the double helix fits the bill.

“DNA is one of the best options, if not the best option, to store archival data especially,” said Chao Pan, a graduate student at the University of Illinois Urbana-Champaign and a co-author on this study.

Its longevity rivaled only by durability, DNA is designed to weather Earth’s harshest conditions — sometimes for tens of thousands of years — and remain a viable data source. Scientists can sequence fossilized strands to uncover genetic histories and breathe life into long-lost landscapes.

Despite its diminutive stature, DNA is a bit like Dr. Who’s infamous police box: bigger on the inside than it appears.

“Every day, several petabytes of data are generated on the internet. Only one gram of DNA would be sufficient to store that data. That’s how dense DNA is as a storage medium,” said Tabatabaei, who is also a fifth-year Ph.D. student.

Another important aspect of DNA is its natural abundance and near-infinite renewability, a trait not shared by the most advanced data storage system on the market today: silicon microchips, which often circulate for just decades before an unceremonious burial in a heap of landfilled e-waste.

“At a time when we are facing unprecedented climate challenges, the importance of sustainable storage technologies cannot be overestimated. New, green technologies for DNA recording are emerging that will make molecular storage even more important in the future,” said Olgica Milenkovic, the Franklin W. Woeltge Professor of Electrical and Computer Engineering and a co-PI on the study.

Envisioning the future of data storage, the interdisciplinary team examined DNA’s millennia-old MO. Then, the researchers added their 21st-century twist.

In nature, every strand of DNA contains four chemicals — adenine, guanine, cytosine, and thymine — often referred to by the initials A, G, C, and T. They arrange and rearrange themselves along the double helix into combinations that scientists can decode, or sequence, to make meaning.

The researchers expanded DNA’s already broad capacity for information storage by adding seven synthetic nucleobases to the existing four-letter lineup.

“Imagine the English alphabet. If you only had four letters to use, you could only create so many words. If you had the full alphabet, you could produce limitless word combinations. That’s the same with DNA. Instead of converting zeroes and ones to A, G, C, and T, we can convert zeroes and ones to A, G, C, T, and the seven new letters in the storage alphabet,” Tabatabaei said.

Because this team is the first to use chemically modified nucleotides for information storage in DNA, members innovated around a unique challenge: not all current technology is capable of interpreting chemically modified DNA strands. To solve this problem, they combined machine learning and artificial intelligence to develop a first-of-its-kind DNA sequence readout processing method.

Their solution can discern modified chemicals from natural ones, and differentiate each of the seven new molecules from one another.

“We tried 77 different combinations of the 11 nucleotides, and our method was able to differentiate each of them perfectly,” Pan said. “The deep learning framework as part of our method to identify different nucleotides is universal, which enables the generalizability of our approach to many other applications.”

This letter-perfect translation comes courtesy of nanopores: proteins with an opening in the middle through which a DNA strand can easily pass. Remarkably, the team found that nanopores can detect and distinguish each monomer unit along the DNA strand — whether the units have natural or chemical origins.

“This work provides an exciting proof-of-principle demonstration of extending macromolecular data storage to non-natural chemistries, which hold the potential to drastically increase storage density in non-traditional storage media,” said Charles Schroeder, the James Economy Professor of Materials Science and Engineering and a co-PI on this study.

DNA made history by storing genetic information. By the looks of this study, the future of data storage is just as double-helical.

Terahertz light-driven spin-lattice control can open up a new path to faster storage

Tyler O'Neal, Staff Editor STORAGE

An international team of researchers from the University of Cologne (Germany), Radboud University Nijmegen (The Netherlands), the Ioffe Institute, and the Prokhorov General Physics Institute (Russia) has discovered a new mechanism to control spin-lattice interaction using ultrashort terahertz (THz) pulses (terahertz means 1012 hertz). This mechanism can open up new and elegant ways to control the propagation of spin waves and thus make an important step to conceptually new technologies of data processing in the future. The results have been published in a recent Science publication entitled ‘Terahertz light-driven coupling of antiferromagnetic spins to lattice’.

Currently, magnetic data recording is dominating data storage technology. It is estimated that soon, more than 7% of the world’s energy production will be spent on data storage centers. Hence there is an urgent demand to develop new technologies to process and store data using ultrafast processes in an energy-efficient manner. 

Spin-lattice interaction plays a decisive role in magnetic recording processes, where a spin is the elementary magnetic moment of an electron, whose orientation control (up and down) is the base of modern binary computer systems.  The scientists used special antiferromagnets in their study – materials in which the ordered spins of electrons align in a regular pattern with neighboring spins pointing in opposite directions. The collective motion of spins in these materials, so-called spin waves, are typically 10 times faster than their counterparts in traditional ferromagnetic materials. In contrast to electrons, such spin waves practically do not interact with the crystal lattice and thus can propagate over macroscopic distances without losses. In the future, spintronics could replace traditional electronics and function as a carrier of information in a magnetic material. This brings the potential for much faster and efficient data processing. At the same time, the weak interaction makes control over the propagation of the spin waves challenging. The scientists then ‘drive’ the spin-lattice coupling by applying an ultrashort terahertz pulse.

Dr. Evgeny Mashkovich, Senior Researcher at the Optical Condensed Matter Science group at the University of Cologne’s Institute for Experimental Physics said: "We showed that we can now control the interaction between lattice and spin waves and make it a strong interaction. I believe that this discovery is an important step towards conceptually new technologies for ultra-fast data processing and efficient data storage in the future."