Tyler O'Neal, Staff Editor HEALTH

Tokyo University of Science advances spintronics by controlling the magnetization direction of magnetite at room temperature

Over the last few decades, conventional electronics has been rapidly reaching its technical limits in computing and information technology, calling for innovative devices that go beyond the mere manipulation of electron current. In this regard, spintronics, the study of devices that exploit the "spin" of electrons to perform functions, is one of the hottest areas in applied physics. But, measuring, altering, and, in general, working with this fundamental quantum property is no mean feat. CAPTION Creating high-density spintronic memory devices with large capacity and even neuromorphic devices that mimic biological neural systems.

Current spintronic devices--for example, magnetic tunnel junctions--suffer from limitations such as high-power consumption, low operating temperatures, and severe constraints in material selection. To this end, a team of scientists at Tokyo University of Science and the National Institute for Materials Science (NIMS), Japan, has recently published a study in ACS Nano, in which they present a surprisingly simple yet efficient strategy to manipulate the magnetization angle in magnetite (Fe3O4), a typical ferromagnetic material. The team fabricated an all-solid reduction-oxidation ("redox") transistor containing a thin film of Fe3O4 on magnesium oxide and a lithium silicate electrolyte doped with zirconium (Fig. 1). The insertion of lithium ions in the solid electrolyte made it possible to achieve rotation of the magnetization angle at room temperature and significantly change the electron carrier density. Associate Professor Tohru Higuchi from Tokyo University of Science, one of the authors of this published paper, says "By applying a voltage to insert lithium ions in a solid electrolyte into a ferromagnet, we have developed a spintronic device that can rotate the magnetization with lower power consumption than that in magnetization rotation by spin current injection. This magnetization rotation is caused by the change of spin-orbit coupling due to electron injection into a ferromagnet." CAPTION Figure 1. After applying an external voltage, lithium ions flow through the reduction-oxidation transistor and reach the bottom magnetite film, altering its charge carrier concentration and modifying the orientation of Fe spins. CREDIT Tohru Higuchi, Tokyo University of Science{module INSIDE STORY}

Unlike previous attempts that relied on using strong external magnetic fields or injecting spin-tailored currents, the new approach leverages a reversible electrochemical reaction. After applying an external voltage, lithium ions migrate from the top lithium cobalt oxide electrode and through the electrolyte before reaching the magnetic Fe3O4 layer. These ions then insert themselves into the magnetite structure, forming LixFe3O4 and causing a measurable rotation in its magnetization angle owing to an alteration in charge carriers.

This effect allowed scientists to reversibly change the magnetization angle by approximately 10°. Although a much greater rotation of 56° was achieved by upping the external voltage further, they found that the magnetization angle could not be switched back entirely (Fig. 2). "We determined that this irreversible magnetization angle rotation was caused by a change in the crystalline structure of magnetite due to an excess of lithium ions," explains Higuchi, "If we could suppress such irreversible structural changes, we could achieve a considerably larger magnetization rotation." CAPTION Figure 2. The change in magnetization angle become noticeable under external voltages higher than 0.7 V, yielding a reversible change of about 10°. At voltages higher than 1.2 V, the rotation is more pronounced but becomes irreversible due to permanent structural changes in the magnetite phase. CREDIT Tohru Higuchi, Tokyo University of Science {module INSIDE STORY}

The novel device developed by scientists represents a big step in the control of magnetization for the development of spintronic devices. Moreover, the structure of the device is relatively simple and easy to fabricate. Dr. Takashi Tsuchiya, Principal Researcher at NIMS, the corresponding author of the study says, "By controlling the magnetization direction at room temperature due to the insertion of lithium ions into Fe3O4, we have made it possible to operate with much lower power consumption than the magnetization rotation by spin current injection. The developed element operates with a simple structure."

Although more work remains to be done to take full advantage of this new device, the imminent rise of spintronics will certainly unlock many novel and powerful applications. "In the future, we will try to achieve a rotation of 180° in the magnetization angle," says Dr Kazuya Terabe, Principal Investigator at the International Center for Materials Nanoarchitectonics at NIMS and a co-author of the study, "This would let us create high-density spintronic memory devices with large capacity and even neuromorphic devices that mimic biological neural systems." Some other applications of spintronics are in the highly coveted field of quantum supercomputing.

Only time will tell what this frontier technology has in line for us!

Missouri S&T researchers use federated learning to improve data security in smart devices

Tyler O'Neal, Staff Editor HEALTH

Companies that make internet-connected household devices need user data to improve their products. But customers want assurances that their private information is secure. So how can companies secure private data and improve future products? The answer is machine learning, according to researchers at Missouri University of Science and Technology. 

Missouri S&T researchers want to ensure that the Internet of Things (IoT)-collected data is accurate and usable, while still protecting the items from malicious attacks or invasions of privacy. IoT is physical objects with sensors and software that are connected to the internet. Researchers say that improving a machine-learning technique called federated learning could allow companies to develop new ways to collect anonymous, but accurate, data from users. 

Federated learning trains algorithms with access to multiple individual devices that hold local data. Federated learning doesn't exchange data with the items, which means there is no central dataset or server where all the information is stored. With the lack of shared data in federated learning, concerns such as privacy, security, and access rights could become a non-issue. 

“Federated learning is a game-changer for IoT because it enables machine learning without needing the learner to directly access customer data,” says Dr. Sajal Das, the Daniel C. St. Clair Chair of computer science at S&T. “IoT provides a fertile ground for applying federated learning to private devices that are rich in data.”   {module INSIDE STORY} Image caption: A smart phone is used to operate the lighting and windows within a Missouri S&T Solar Village home. Photo by Sam O’Keefe, Missouri S&T.

Das warns that IoT devices are vulnerable to dynamic environments and attacks from outside sources with erroneous data. Therefore, he says collecting data in a federated manner is crucial.

Das and his co-investigator Dr. Tony Luo, an associate professor of computer science at S&T, are designing new federated learning algorithms with funding from the National Science Foundation and are putting data safety and accuracy above all else in their work. 

“By collecting data from numerous IoT devices without compromising privacy or network capabilities, our methods will allow for growth in the way these devices work and measure data,” says Das. “Our new algorithms will combat erroneous data by designing novel incentive mechanisms to motivate and encourage users who contribute accurate data.” 

Das and Luo hope that users will be willing to contribute data to machine learning while having confidence that the data is not identifiable. That way, the data can be used to push the boundaries of complexity and performance for IoT items. 

Das says that the research has the potential to produce tremendous benefits to personalized industries such as health care. 

“In smart health care, wearable IoT devices can help measure an individual’s health conditions such as vital records, physical activities and food intake,” says Das. “For example, without directly accessing a patient’s sensitive and private information, our novel federated learning approach can investigate how diseases like diabetes are influenced by lifestyle and demography and whether there is a correlation with other health conditions like hypertension.”

Das says that with enough advances in the secure and accurate collection of IoT data, new devices could serve more and better purposes while easing the minds of those who are reluctant to accept smart technology into their homes. 

Swiss researcher builds new system for drying fruit by means of ionic wind

Tyler O'Neal, Staff Editor HEALTH

After the summer harvest, fruits are sold as dried products suitable for the current season. However, if fruit or vegetables are dried with heat, nutrients can be destroyed and flavors can be reduced. This is why non-thermal drying of food – i.e. without heating – is preferred by the industry. Among other things, fans are used for this purpose. A new drying process developed at Empa using ionic wind promises to make the non-thermal drying of food much more energy-efficient, faster, and even gentler.

When the blades of a fan rotate, the steady wind is blowing as a result. This phenomenon is well known from everyday life, and so we use the fan on hot summer days to cool us down. An unwanted side effect is the unpleasant feeling in the eyes, which becomes drier and drier due to the artificial wind. The food industry has been taking advantage of this effect for a long time: Fruit and veggies are preferably dried without heat because heat deteriorates nutrients and flavor.

The so-called non-thermal convective drying of food with the help of large fans has a drawback, however: The drying process is time-consuming and requires a lot of energy. This is why the industry has been looking to find a more energy-efficient method for a long time. One alternative technology is based on the so-called ionic wind. Although this already works on a small scale, attempts to upscale the concept for the industry have failed so far. Empa researchers have now developed a more energy-efficient drying system based on ionic wind, which is perfectly suitable for industrial applications.

Wind, without any moving components

The ionic wind is not generated by the rotating blades of a fan; it is created by connecting, for instance, a metal wire to a high-voltage source with a positive voltage of 10,000 to 30,000 volts. This charges the wire positively and ionizes the surrounding air. Air consists of various gases such as oxygen (O2), nitrogen (N2), or carbon dioxide (CO2). Each of these molecules consists of atoms, which in turn consist of positively charged elementary particles – the protons – and negatively charged particles – the electrons. The electrons are attracted by the positively charged wire, while the much heavier protons are repelled by the wire. These electrostatic forces ultimately cause electrons to "split off" from the (electrically neutral) gas molecules, the remaining molecules are now positively charged – or "ionized". The positive ions collide with other air molecules on their way away from the wire towards the grounded collector located below the wire and set them in motion. This impulse, or rather the particle movement triggered by it, then creates the ionic wind, which is also known as electrohydrodynamic airflow.

Small but powerful!

Researchers tried to make use of ionic wind with different approaches for the industrial drying of food – but so far without remarkable success because an upscaling was not possible. Empa researcher Thijs Defraeye from the "Biomimetic Membranes and Textiles" lab and his team pursued the idea further and varied various process parameters. First, the researchers did not place the food to be dried on a tray as it was done previously but used a mesh instead. "Now this isn't exactly rocket science, but so far no one has considered this adaptation for the drying with the ionic wind," says the Empa researcher.

What sounds like a small change makes a huge difference, though: The water can now evaporate from all sides of the fruits or vegetables. As a result, the ionic wind dries the food twice as fast as on an impermeable tray, which was used by researchers over the world so far. But above all, the ionic wind dries fruit and vegetables more uniformly on the mesh. In contrast to the previous approaches of electrohydrodynamic drying, the new design is also easier to scale up – and thus extremely interesting for industry. Drying with ionic wind: If the fruit slices are placed on a mesh, they are dried faster and more evenly. Image: Empa{module INSIDE STORY}

A new system – from supercomputer modeling

In refining their new concept further, Empa researchers relied on complex supercomputer simulations. This allows various dryer device adjustments and their influence on the drying process to be simulated virtually. Hence, the system can be optimized "in silico" without having to physically build new drying equipment each time.

But can the results of the supercomputer calculation be successfully transferred into the real world? Is it really possible to optimize the process in this way? In cooperation with researchers from Dalhousie University in Canada, a first prototype of the new drying system was built in their lab. Initial tests did indeed show considerable improvements: Drying by means of ionic wind is much faster and consumes less than half the energy required by conventional processes. In addition, the food is dried more evenly and the nutrients are preserved much better. Last but not least, the process can be scaled up to an industrial-scale rather easily. Defraeye and his team are currently working with a Swiss retailer to develop the concept further.