Aurelia Butler

A research effort led by scientists at the U.S. Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL) has made advances that could enable a broader range of currently unimagined optoelectronic devices.
The researchers, whose previous innovation included incorporating a perovskite layer that allowed the creation of a new type of polarized light-emitting diode (LED) that emits spin-controlled photons at room temperature without the use of magnetic fields or ferromagnetic contacts, now have gone a step further by integrating a III-V semiconductor optoelectronic structure with a chiral halide perovskite semiconductor. That is, they transformed an existing commercialized LED into one that also controls the spin of electrons. The results provide a pathway toward transforming modern optoelectronics, a field that relies on the control of light and encompasses LEDs, solar cells, and telecommunications lasers, among other devices.
“It’s up to one’s imagination where this might go or where this might end up,” said Matthew Beard, a senior research fellow at NREL and coauthor of the newly published Nature article, “Room temperature spin injection across a chiral-perovskite/III-V interface.”
Beard also serves as director of the Center for Hybrid Organic Inorganic Semiconductors for Energy (CHOISE), an Energy Frontier Research Center funded by the Office of Science Basic Energy Sciences within DOE. The reported research was funded by CHOISE and relied on a broad range of scientific expertise drawn from NREL, the Colorado School of Mines, University of Utah, University of Colorado Boulder, and the Universite de Lorraine in France.
The goal of CHOISE is to understand control over the interconversion of charge, spin, and light using carefully designed chemical systems. In particular, the work focuses on control over the electron spin that can be either “up” or “down.” Most current-day optoelectronic devices rely on the interconversion between charge and light. However, spin is another property of electrons, and control over the spin could enable a wide plethora of new effects and functionality. The researchers published a paper in 2021 in which they reported how by using two different perovskite layers they were able to control the spin by creating a filter that blocks electrons “spinning” in the wrong direction.
They hypothesized at the time that advancements could be made in optoelectronics if they could successfully incorporate the two semiconductors, and then went on to do just that. The breakthroughs made, which include eliminating the need for subzero Celsius temperatures, can be used to increase data processing speeds and decrease the amount of power needed.
“Most current-day technologies are all based on controlling charge,” Beard said. “Most people just forget about the electron spin, but spin is very important, and it’s also another parameter that one can control and utilize.”
Manipulating the spin of electrons in a semiconductor has previously required the use of ferromagnetic contacts under an applied magnetic field. Using chiral perovskites, the researchers were able to transform an LED to one that emits polarized light at room temperature and without a magnetic field. Chirality refers to the material’s structure that cannot be superimposed on its mirror image, such as a hand. For example, a “left-handed” oriented chiral system may allow transport of electrons with “up” spins but block electrons with “down” spins, and vice versa. The spin of the electron is then converted to the “spin,” or polarization, of the emitted light. The degree of polarization, which measures the intensity of light that is polarized in one direction, reached about 2.6% in the previous research. The addition of the III-V semiconductor — which is made of materials in the third and fifth columns of the periodic table — boosted the polarization to about 15%. The degree of polarization serves as a direct measure of spin accumulation in the LED.
“This work is particularly exciting to me, as it combines spin functionality with a traditional LED platform,” said the first author of the work, Matthew Hautzinger. “You can buy an LED analogous to what we used for 14 cents, but with the chiral perovskite incorporated, we’ve transformed an already robust (and well understood) technology into a futuristic spin-control device.” More

Extreme weather events such as hurricanes and storms have increased in both frequency and severity in recent years.
With that has come heightened public interest, resulting in often dramatic footage being live-streamed on platforms such as YouTube, TikTok and Discord.
Now, a new study conducted at the University of Plymouth has for the first time analysed what might be motivating people to watch these streams — in some instances for up to 12 hours at a time.
The research centred around the live-streaming of three events — Hurricane Irma in 2017, Hurricane Ian in 2022, and Storms Dudley, Eunice and Franklin in 2022.
Through a detailed analysis of viewers’ comments, it was found that people in affected areas were using streams to discuss official government risk advice they had received — for example, about whether to evacuate.
Others were drawn to the streams because they had a previous connection to the affected region. For these people, watching live footage — which included taking time to share messages of ‘hope’ for the hurricane or storm to pass without destruction — was a way of showing support to places and people impacted by the event.
The research was published in the journal Environmental Hazards and conducted by Dr Simon Dickinson, Lecturer in Geohazards and Risk in the University’s School of Geography, Earth and Environmental Sciences.

He said: “When dramatic things happen — whether that relates to extreme weather or events like tornados or volcanoes erupting — people flock to watch. You might assume that this is just a form of online ‘rubber-necking, and that people are naturally drawn to spectacular sights. However, this study has shown that the drivers to watch extreme weather footage are more complex. Live-streams provide the opportunity for people in, close to, and far away from the event to interact in real time. The footage becomes a marker that people use to sense-check their understandings of how significant the event is, how hazards work, and as an online gathering point to share experiences of similar events. It is a fascinating insight into human behaviour that has previously been unexplored.”
The research focused on nine live-streams of the 2017 and 2022 hurricanes and storms, which broadcast a total of 65 hours of video footage watched by more than 1.8 million people.
During that time, over 14,300 comments were left by 5,000 unique accounts, a reflection of the fact that footage focused on unfolding events of national or global importance generate higher-than-normal audience engagement.
Many of the streams were already existing webcam channels that were repurposed during the hurricane or storm, such as webcams that streamed beach or port conditions. In some instances, affected people streamed live-footage from their own house security or doorbell cameras.
The study demonstrates that people are keen to learn more about the science behind what is happening, highlighting the need for further work that examines how people are using new technologies to make sense of hazard risk.
Dr Dickinson added: “Although scientists are getting better at communicating risk, people are far more likely to discuss hazards in informal and relatively unmoderated settings. Moments of extreme weather are important because they focus people’s attention and generate discussion about hazards, how they work, and how they will increasingly affect us in future. New digital practices — such as live-streaming — are thus important for us to understand because they’re not just spaces of disaster voyeurism. Rather, they’re spaces of learning, community and emotional support in a world that can feel increasingly volatile.” More

The open-access Journal of the American Chemical Society (JACS Au) has just published an invited perspective by Dr Saer Samanipour and his team on the daunting challenge of mapping all the chemicals around us. Samanipour, an Assistant Professor at the Van ‘t Hoff Institute for Molecular Sciences of the University of Amsterdam (UvA) takes inventory of the available science and concludes that currently a real pro-active chemical management is not feasible. To really get a grip on the vast and expanding chemical universe, Samanipour advocates the use of machine learning and AI, complementing existing strategies for detecting and identifying all molecules we are exposed to.
In science lingo the aggregate of all the molecules we are exposed to is called the ‘exposome chemical space’ and it is central to Samanipour’s scientific endeavours. It is his mission to explore this vast molecular space and map it to the most ‘remote’ corners. He is driven by curiosity, but even more so by necessity. Direct and indirect exposure to a myriad of chemicals, mostly unknown, poses a significant threat to the human health. For instance, estimates are that 16% of global premature deaths are linked to pollution. The environment suffers as well, which can be seen, for example, in the loss of biodiversity. The case can be made, according to Samanipour, that humankind has surpassed the safe operating space for introducing human-made chemicals into the system of planet Earth.
Current approach is inherently passive
“It is rather unsatisfactory that we know so little about this,” he says. “We know little about the chemicals already in use, let alone that we can keep up with new chemicals that are currently being manufactured at an unprecedented rate.” In a previous study, he estimated that less than 2% of all chemicals that we are exposed to have been identified.
“The way society approaches this issue is inherently passive and at best reactive. Only after we observe some sort of effects of exposure to chemicals do we feel the urge to analyse them. We attempt to determine their presence, their effect on the environment and human health, and we try to determine the mechanisms by which they cause any harm. This has led to many problems, the latest being the crisis with PFAS chemicals. But we have also seen major issues with flame retardants, PCBs, CFCs and so on.”
Moreover, regulatory measures are predominantly aimed at chemicals with a very specific molecular structure that are produced in large quantities. “There are countless numbers of other chemicals out there where we don’t know much about. And these are not only man-made; nature also produces chemicals that can harm us. Through purely natural synthetic routes, or through the transformation of human-made chemicals.” In particular the latter category has been systematically overlooked according to Samanipour. “Conventional methods have catalogued only a fraction of the exposome, overlooking transformation products and often yielding uncertain results.”
We need a data-driven approach
The paper in JACS Au thoroughly reviews the latest efforts in mapping the exposome chemical space and discusses their results. A main bottleneck is that conventional chemical analysis is biased towards known or proposed structures, since this is key to interpreting data obtained with analytical methods such as chromatography and mass spectrometry (GC/LC-HRMS). Thus the more ‘unexpected’ chemicals are overlooked. This bias is avoided in so-called non-targeted analysis (NTA), but even then results are limited. Over the past 5 years, 1600 chemicals have been identified while every year around 700 new chemicals are introduced into the US market alone. Samanipour: “When you take the potential transformation products of these novel chemicals into account, you have to conclude that the speed of NTA studies is far too slow to be able to catch up. At this rate, our chemical exposome will continue to remain unknown.”

The paper lists these and many more bottlenecks in current analytical science and suggest ways to improve results. In particular the use of machine learning and artificial intelligence will really push the field ahead, Samanipour argues. “We need a data-driven approach along several lines. Firstly, we should intensify the datamining efforts to distil information from existing chemical databases. Already recorded relations between structure, exposure and effect of identified chemicals will lead us to new insights. They could for instance help predict the health effects of related chemicals that are yet unidentified. Secondly, we have to perform retrospective analysis on already available analytical data obtained with established methods, expanding the identified chemical space. We will for sure find molecules there that have been overlooked until now. And thirdly, we can use AI to work on understanding the structure and scope of the exposome chemical space.”
Work hard to tackle this
Of course all this is a very complex, daunting matter, Samanipour realises. But as a sort of astronaut in molecular space — just like the explorers of the factual universe — he won’t let that complexity put him off. “We have to work hard to tackle this. I have no illusion that during my scientific career we will be able to fully chart the exposome chemical space. But it is imperative that we face its complexity, discuss it and take the first steps towards getting to grips with it.”
Samanipour cooperated with colleagues at the UvA’s Institute for Biodiversity and Ecosystem Dynamics, the School of Public Health at Imperial College London (United Kingdom) and the Queensland Alliance for Environmental Health Sciences at the University of Queensland (Australia). The work was supported by the TKI ChemistryNL and the UvA Data Science Center, with additional local funding for the partners in the UK and Australia. More

A study by Stefano Battiston of the Department of Finance at the University of Zurich and his co-authors has identified critical shortcomings in the way climate-related risks to corporate assets are currently assessed. Many current estimates of climate physical climate risk rely on simplified and proxy data that do not accurately represent a company’s true risk exposure. This can lead to significant underestimates of climate-related losses, with serious implications for business investment planning, asset valuation and climate adaptation efforts.
Potential losses up to 70% higher than previously estimated
The research team developed a new methodology that uses detailed information about the location and characteristics of a company’s physical assets, such as factories, equipment and natural resources. This approach provides a more accurate picture of climate risks than methods that use proxy data, which often assume that all of a company’s assets are located at its headquarters. “When we compared our results with those using proxy data, we found that the potential losses from climate risks could be up to 70% higher than previously thought,” says Stefano Battiston. “This underscores the critical need for more granular data in risk assessments.”
Preparing for the worst: The role of extreme events
The authors also point to the importance of considering “tail risk” in climate assessments. Tail risk refers to the possibility of extreme events that, while rare, can have catastrophic impacts. “Many assessments focus on average impacts. Our research shows that the potential losses from extreme events can be up to 98% higher than these averages suggest,” says Stefano Battiston. “Failure to account for these possibilities can leave businesses and investors dangerously unprepared.”
More funding for climate adaptation
The study’s findings have significant implications for climate policy, business strategy, and investment decisions. The researchers emphasize that more accurate risk assessments are crucial for developing effective climate adaptation strategies and determining appropriate levels of climate-related insurance and funding. “Our work shows that we may be seriously underestimating the financial resources needed for climate adaptation,” concludes Stefano Battiston. More

Physicists from Swansea University and Åbo Akademi University have made a significant breakthrough in solar cell technology by developing a new analytical model that improves the understanding and efficiency of thin-film photovoltaic (PV) devices.
For nearly eight decades, the so-called Shockley diode equation has explained how current flows through solar cells; the electrical current that powers up your home or charges the battery bank. However, the new study challenges this traditional understanding for a specific class of next-generation solar cells, namely: thin-film solar cells.
These thin-film solar cells, made of flexible, low-cost materials have had limited efficiency due to factors that the existing analytical models couldn’t fully explain.
The new study sheds light on how these solar cells achieve optimal efficiency. It reveals a critical balance between collecting the electricity generated by light and minimising losses due to recombination, where electrical charges cancel each other out.
“Our findings provide key insights into the mechanisms driving and limiting charge collection, and ultimately the power-conversion efficiency, in low-mobility PV devices,” said the lead author, Dr Oskar Sandberg of Åbo Akademi University, Finland.
New Model Captures the Missing Piece
Previous analytical models for these solar cells had a blind spot: “injected carriers” — charges entering the device from the contacts. These carriers significantly impact recombination and limited efficiency.

“The traditional models just weren’t capturing the whole picture, especially for these thin-film cells with low-mobility semiconductors,” explained the principal investigator, Associate Professor Ardalan Armin of Swansea University. “Our new study addresses this gap by introducing a new diode equation specifically tailored to account for these crucial injected carriers and their recombination with those photogenerated.”
“The recombination between injected charges and photogenerated ones is not a huge problem in traditional solar cells such as silicon PV which is hundreds of times thicker than next generation thin film PV such as organic solar cells,” Dr Sandberg added.
Associate Professor Armin said: “One of the brightest theoretical physicists of all times, Wolfgang Pauli once said ‘God made the bulk; the surface was the work of the devil’. As thin film solar cells have much bigger interfacial regions per bulk than traditional silicon; no wonder why they get affected more drastically by “the work of the devil” — that is recombination of precious photogenerated charges with injected ones near the interface!”
Impact on Future Solar Cell Development
This new model offers a new framework for designing more efficient thin solar cells and photodetectors, optimising existing devices, and analysing material properties. It can also aid in training machines used for device optimisation marking a significant step forward in the development of next-generation thin-film solar cells. More

State-of-the-art prosthetic limbs can help people with amputations achieve a natural walking gait, but they don’t give the user full neural control over the limb. Instead, they rely on robotic sensors and controllers that move the limb using predefined gait algorithms.
Using a new type of surgical intervention and neuroprosthetic interface, MIT researchers, in collaboration with colleagues from Brigham and Women’s Hospital, have shown that a natural walking gait is achievable using a prosthetic leg fully driven by the body’s own nervous system. The surgical amputation procedure reconnects muscles in the residual limb, which allows patients to receive “proprioceptive” feedback about where their prosthetic limb is in space.
In a study of seven patients who had this surgery, the MIT team found that they were able to walk faster, avoid obstacles, and climb stairs much more naturally than people with a traditional amputation.
“This is the first prosthetic study in history that shows a leg prosthesis under full neural modulation, where a biomimetic gait emerges. No one has been able to show this level of brain control that produces a natural gait, where the human’s nervous system is controlling the movement, not a robotic control algorithm,” says Hugh Herr, a professor of media arts and sciences, co-director of the K. Lisa Yang Center for Bionics at MIT, an associate member of MIT’s McGovern Institute for Brain Research, and the senior author of the new study.
Patients also experienced less pain and less muscle atrophy following this surgery, which is known as the agonist-antagonist myoneural interface (AMI). So far, about 60 patients around the world have received this type of surgery, which can also be done for people with arm amputations.
Hyungeun Song, a postdoc in MIT’s Media Lab, is the lead author of the paper, which will appear in Nature Medicine.
Sensory feedback
Most limb movement is controlled by pairs of muscles that take turns stretching and contracting. During a traditional below-the-knee amputation, the interactions of these paired muscles are disrupted. This makes it very difficult for the nervous system to sense the position of a muscle and how fast it’s contracting — sensory information that is critical for the brain to decide how to move the limb.

People with this kind of amputation may have trouble controlling their prosthetic limb because they can’t accurately sense where the limb is in space. Instead, they rely on robotic controllers built into the prosthetic limb. These limbs also include sensors that can detect and adjust to slopes and obstacles.
To try to help people achieve a natural gait under full nervous system control, Herr and his colleagues began developing the AMI surgery several years ago. Instead of severing natural agonist-antagonist muscle interactions, they connect the two ends of the muscles so that they still dynamically communicate with each other within the residual limb. This surgery can be done during a primary amputation, or the muscles can be reconnected after the initial amputation as part of a revision procedure.
“With the AMI amputation procedure, to the greatest extent possible, we attempt to connect native agonists to native antagonists in a physiological way so that after amputation, a person can move their full phantom limb with physiologic levels of proprioception and range of movement,” Herr says.
In a 2021 study, Herr’s lab found that patients who had this surgery were able to more precisely control the muscles of their amputated limb, and that those muscles produced electrical signals similar to those from their intact limb.
After those encouraging results, the researchers set out to explore whether those electrical signals could generate commands for a prosthetic limb and at the same time give the user feedback about the limb’s position in space. The person wearing the prosthetic limb could then use that proprioceptive feedback to volitionally adjust their gait as needed.
In the new Nature Medicine study, the MIT team found this sensory feedback did indeed translate into a smooth, near-natural ability to walk and navigate obstacles.

“Because of the AMI neuroprosthetic interface, we were able to boost that neural signaling, preserving as much as we could. This was able to restore a person’s neural capability to continuously and directly control the full gait, across different walking speeds, stairs, slopes, even going over obstacles,” Song says.
A natural gait
For this study, the researchers compared seven people who had the AMI surgery with seven who had traditional below-the-knee amputations. All of the subjects used the same type of bionic limb: a prosthesis with a powered ankle as well as electrodes that can sense electromyography (EMG) signals from the tibialis anterior the gastrocnemius muscles. These signals are fed into a robotic controller that helps the prosthesis calculate how much to bend the ankle, how much torque to apply, or how much power to deliver.
The researchers tested the subjects in several different situations: level-ground walking across a 10-meter pathway, walking up a slope, walking down a ramp, walking up and down stairs, and walking on a level surface while avoiding obstacles.
In all of these tasks, the people with the AMI neuroprosthetic interface were able to walk faster — at about the same rate as people without amputations — and navigate around obstacles more easily. They also showed more natural movements, such as pointing the toes of the prosthesis upward while going up stairs or stepping over an obstacle, and they were better able to coordinate the movements of their prosthetic limb and their intact limb. They were also able to push off the ground with the same amount of force as someone without an amputation.
“With the AMI cohort, we saw natural biomimetic behaviors emerge,” Herr says. “The cohort that didn’t have the AMI, they were able to walk, but the prosthetic movements weren’t natural, and their movements were generally slower.”
These natural behaviors emerged even though the amount of sensory feedback provided by the AMI was less than 20 percent of what would normally be received in people without an amputation.
“One of the main findings here is that a small increase in neural feedback from your amputated limb can restore significant bionic neural controllability, to a point where you allow people to directly neurally control the speed of walking, adapt to different terrain, and avoid obstacles,” Song says.
“This work represents yet another step in us demonstrating what is possible in terms of restoring function in patients who suffer from severe limb injury. It is through collaborative efforts such as this that we are able to make transformational progress in patient care,” says Matthew Carty, a surgeon at Brigham and Women’s Hospital and associate professor at Harvard Medical School, who is also an author of the paper.
Enabling neural control by the person using the limb is a step toward Herr’s lab’s goal of “rebuilding human bodies,” rather than having people rely on ever more sophisticated robotic controllers and sensors — tools that are powerful but do not feel like part of the user’s body.
“The problem with that long-term approach is that the user would never feel embodied with their prosthesis. They would never view the prosthesis as part of their body, part of self,” Herr says. “The approach we’re taking is trying to comprehensively connect the brain of the human to the electromechanics.”
The research was funded by the MIT K. Lisa Yang Center for Bionics, the National Institute of Neurological Disorders and Stroke, a Neurosurgery Research Education Foundation Medical Research Fellowship, and the Eunice Kennedy Shriver National Institute of Child Health and Human Development. More

A team led by University of Maryland computer scientists invented a camera mechanism that improves how robots see and react to the world around them. Inspired by how the human eye works, their innovative camera system mimics the tiny involuntary movements used by the eye to maintain clear and stable vision over time. The team’s prototyping and testing of the camera — called the Artificial Microsaccade-Enhanced Event Camera (AMI-EV) — was detailed in a paper published in the journal Science Robotics in May 2024.
“Event cameras are a relatively new technology better at tracking moving objects than traditional cameras, but -today’s event cameras struggle to capture sharp, blur-free images when there’s a lot of motion involved,” said the paper’s lead author Botao He, a computer science Ph.D. student at UMD. “It’s a big problem because robots and many other technologies — such as self-driving cars — rely on accurate and timely images to react correctly to a changing environment. So, we asked ourselves: How do humans and animals make sure their vision stays focused on a moving object?”
For He’s team, the answer was microsaccades, small and quick eye movements that involuntarily occur when a person tries to focus their view. Through these minute yet continuous movements, the human eye can keep focus on an object and its visual textures — such as color, depth and shadowing — accurately over time.
“We figured that just like how our eyes need those tiny movements to stay focused, a camera could use a similar principle to capture clear and accurate images without motion-caused blurring,” He said.
The team successfully replicated microsaccades by inserting a rotating prism inside the AMI-EV to redirect light beams captured by the lens. The continuous rotational movement of the prism simulated the movements naturally occurring within a human eye, allowing the camera to stabilize the textures of a recorded object just as a human would. The team then developed software to compensate for the prism’s movement within the AMI-EV to consolidate stable images from the shifting lights.
Study co-author Yiannis Aloimonos, a professor of computer science at UMD, views the team’s invention as a big step forward in the realm of robotic vision.
“Our eyes take pictures of the world around us and those pictures are sent to our brain, where the images are analyzed. Perception happens through that process and that’s how we understand the world,” explained Aloimonos, who is also director of the Computer Vision Laboratory at the University of Maryland Institute for Advanced Computer Studies (UMIACS). “When you’re working with robots, replace the eyes with a camera and the brain with a computer. Better cameras mean better perception and reactions for robots.”
The researchers also believe that their innovation could have significant implications beyond robotics and national defense. Scientists working in industries that rely on accurate image capture and shape detection are constantly looking for ways to improve their cameras — and AMI-EV could be the key solution to many of the problems they face.

“With their unique features, event sensors and AMI-EV are poised to take center stage in the realm of smart wearables,” said research scientist Cornelia Fermüller, senior author of the paper. “They have distinct advantages over classical cameras — such as superior performance in extreme lighting conditions, low latency and low power consumption. These features are ideal for virtual reality applications, for example, where a seamless experience and the rapid computations of head and body movements are necessary.”
In early testing, AMI-EV was able to capture and display movement accurately in a variety of contexts, including human pulse detection and rapidly moving shape identification. The researchers also found that AMI-EV could capture motion in tens of thousands of frames per second, outperforming most typically available commercial cameras, which capture 30 to 1000 frames per second on average. This smoother and more realistic depiction of motion could prove to be pivotal in anything from creating more immersive augmented reality experiences and better security monitoring to improving how astronomers capture images in space.
“Our novel camera system can solve many specific problems, like helping a self-driving car figure out what on the road is a human and what isn’t,” Aloimonos said. “As a result, it has many applications that much of the general public already interacts with, like autonomous driving systems or even smartphone cameras. We believe that our novel camera system is paving the way for more advanced and capable systems to come.” More

A research team led by the Department of Energy’s Oak Ridge National Laboratory has bridged a knowledge gap in atomic-scale heat motion. This new understanding holds promise for enhancing materials to advance an emerging technology called solid-state cooling.
An environmentally friendly innovation, solid-state cooling could efficiently chill many things in daily life from food to vehicles to electronics — without traditional refrigerant liquids and gases or moving parts. The system would operate via a quiet, compact and lightweight system that allows precise temperature control.
Although the discovery of improved materials and the invention of higher-quality devices are already helping to promote the growth of the new cooling method, a deeper understanding of material enhancements is essential. The research team used a suite of neutron-scattering instruments to examine at the atomic scale a material that scientists consider to be an optimal candidate for use in solid-state cooling.
The material, a nickel-cobalt-manganese-indium magnetic shape-memory alloy, can be deformed and then returned to its original shape by driving it through a phase transition either by increasing temperature or by applying a magnetic field. When subjected to a magnetic field, the material undergoes a magnetic and structural phase transition, during which it absorbs and releases heat, a behavior known as the magnetocaloric effect. In solid-state cooling applications, the effect is harnessed to provide refrigeration. A key characteristic of the material is its nearness to disordered conditions known as ferroic glassy states, because they present a way to enhance the material’s ability to store and release heat.
Magnons, also known as spin waves, and phonons, or vibrations, couple in a synchronized dance in small regions distributed across the disordered arrangement of atoms that comprise the material. The researchers found that patterns of behavior in these small regions, referred to as localized hybrid magnon-phonon modes in the team’s paper detailing the research, have important implications for the thermal properties of the material.
The scientists revealed that the modes cause the phonons to be significantly altered or shifted by the presence of a magnetic field. The modes also modify the material’s phase stability. These changes can result in fundamental alterations in the material’s properties and behavior that can be tuned and tailored.
“Neutron scattering shows that the cooling capacity of the magnetic shape-memory alloy is tripled by the heat contained within these local magnon-phonon hybrid modes that form because of the disorder in the system,” said ORNL’s Michael Manley, the leader of the study. “This finding reveals a path to make better materials for solid-state cooling applications for societal needs.”
The magnetic shape-memory alloy that the team studied is in a phase that has nearly formed disordered conditions known as spin glass and strain glass — not the familiar glass used in windows and elsewhere but rather unconventional phases of matter that lack order. The magnetic moments, or tiny magnets, associated with the atoms in the spin glass phase are randomly oriented rather than pointing in the same direction. Comparatively, in the strain glass phase, the lattice of atoms is strained at the nanometer scale in a messy and irregular pattern. Spin glass and strain glass are referred to as frustrated conditions in a material because they arise from competing interactions or constraints that prevent the material from achieving a stable ordered state.

“As the material approaches this frustrated state, the amount of heat being stored increases,” Manley said. “Long- and short-range interactions manifest as localized vibrations and spin waves, which means they’re getting trapped in small regions. This is important because these extra localized vibrational states store heat. Changing the magnetic field triggers another phase transition in which this heat is released.”
Controlling the functions of the magnetic shape-memory alloy so that it can be used as a heat sponge could be one way to allow for efficient solid-state cooling without the need for traditional refrigerants or mechanical components.
This study was supported by DOE’s Office of Science Materials Sciences and Engineering Division. A portion of the neutron scattering work for this research was performed at the High Flux Isotope Reactor and the Spallation Neutron Source, DOE Office of Science user facilities at ORNL. The National Institute of Standards and Technology of the Department of Commerce also provided neutron research facilities. More