Recently, the Xiao Group has made a pivotal breakthrough in understanding the electronic noise of a single skyrmion, a microscopic swirling magnetic texture with potential for next-generation computing technologies. The study, published in Physical Review B, delves into how skyrmions interact with materials disorder and external perturbations, revealing distinct noise signatures across different pinning regimes. This insight is crucial for developing low-noise, reliable skyrmion-based devices, marking a significant step towards harnessing skyrmions for advanced applications in data storage, logic circuits, and beyond.
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Research on magnetic skyrmions featured in Brown’s IMPACT magazine
The 2023 edition of IMPACT Research at Brown magazine describes recent research on magnetic skyrmions from the Xiao Group on P. 45.
“Physics department interim chair Gang Xiao, professor of physics and engineering, is building devices that generate skyrmions—disk-like magnetic swirls in two-dimensional metallic films—that can change their polarity, motion, and size when exposed to a magnetic field or an electric current. Xiao is already using skyrmions to generate truly random numbers, which might be useful in cybersecurity and encryption, yet he has his sights set higher. Arrays and networks of skyrmions, he said, could form the basis for tiny yet incredibly efficient computers.
Like traditional silicon computer processors, these devices would still be based on ones and zeros (or, in the case of skyrmions, a larger or smaller size), but the way information flows through the processor would be vastly different. When a skyrmion oscillates its size, it changes the state of its neighbors, creating a cascading effect that is eerily similar to the way neural circuits in the brain function—meaning that this sort of device could make huge strides in computing power while requiring only a small fraction of the energy required by existing computers.
“If you built a silicon computer that mimics the human brain, you’d need a nuclear power plant to run it. But humans only need about ten watts of energy to power our brains. Skyrmions could bring us a lot closer to that sort of fast, low-power computation”, said Xiao.
IMPACT, an annual publication from the Office of the Vice President for Research at Brown University, illuminates the trailblazing work of researchers who are pushing boundaries in their respective fields. This sixth issue of IMPACT continues its tradition of spotlighting influential research contributing to global advancement.
Physics department acknowledges Professor Xiao’s service
In a recent gathering of the Physics Department, faculty, staff and students came together to express their heartfelt appreciation for Professor Gang Xiao, who will be stepping down as the Interim Chair of the department on June 30, 2023. The gathering served as an opportunity to recognize Professor Xiao’s exceptional service following the untimely passing of the department’s former chair, Professor Meenakshi Narain. The presence of Brown’s Interim Provost, Professor Lawrence Larson, further highlighted the significance of Professor Xiao’s leadership and service during this challenging period.
Amidst the gathering, Professor Xiao humbly conveyed his sincere gratitude to the entire physics community. He emphasized the vital role played by every member of the department in ensuring a smooth transition after the tragic loss of the department’s beloved Chair Narain. Their dedication and collaboration were pivotal in upholding the department’s mission.
As Professor Xiao concludes his tenure as Interim Chair, he looks forward to dedicating himself to research and teaching. His passion for scientific exploration and discovery, coupled with his commitment to training future scientists and engineers, will be the driving force behind his endeavors moving forward.
Junhang Duan receives physics department’s ScM research excellence award
Junhang Duan, a talented master student researcher from Professor Xiao’s Group, has been recognized with the ScM Research Excellence Award by the Physics department. Her research on the physics of magnetic skyrmion and domain wall motion, conducted under the guidance of Professor Gang Xiao, has earned her this well-deserved recognition.
Upon completing her master’s studies, Junhang will continue her academic journey as a PhD student at Northwestern University, beginning this Fall semester.
Congratulations to Junhang on this significant achievement, and we wish her the best of luck in her future research endeavors at Northwestern!
Professor Xiao gave a lecture for the FCMP Columbia 2023 Spring Series
Professor Xiao gave a lecture for the “Frontiers of Condensed Matter Physics” (FCMP) Columbia 2023 Spring Series on April 3rd, 2023. The lecture, titled “Generating true random numbers with single skyrmions: exploring local dynamics and skyrmion interactions”, is part of a lecture series featuring leading CMP-AMO researchers sharing their latest findings and insights.
About FCMP: Since 2011, Columbia University has been hosting the “Frontiers of Condensed Matter Physics (FCMP) Lectures” to bring in leading CMP/AMO researchers and provide a platform for them to present their latest research to a diverse audience comprising graduate students, postdocs, and senior researchers. The lectures aim to be historically, pedagogically, and intuitively presented to enable even entry-level CMP graduate students to enjoy and gain valuable insights from them.
In response to the ongoing pandemic, the lectures have been moved fully online since 2020, and recordings of the lectures are made available to subscribed students and interested observers from the research community. The FCMP is organized by Professor Yasutomo Uemura of Columbia University. The 2023 Spring series is co-hosted by Professors Philip Kim (Harvard), Pengcheng Dai (Rice), Liuyan Zhao (Michigan), and Weiwei Xie (Michigan State), who circulate flyers among their groups and institutions and recommend speakers. The lecture series promises to be an exciting and informative event for all those interested in the latest developments in condensed matter physics.
Professor Xiao gave an invited talk on single skyrmion true random number generator at APS March Meeting
On March 8, 2023, Professor Xiao gave an invited talk at the APS March Meeting 2023 in Las Vegas, NV. The talk was part of Session M44 on Topological Magnetic Textures and was titled “Single skyrmion true random number generator using local dynamics and interaction between skyrmions”.
During the talk, Professor Xiao discussed the creation of a single skyrmion true random number generator, which utilizes local dynamics, and a multi-skyrmion system whose dynamics is influenced by the interaction between skyrmions. This new physics could have implications for a range of fields, from cryptography to probabilistic computing.
The video recording of Professor Xiao’s talk is available till June 20, 2023 on APS March Meeting website. Access to the recording requires APS March Meeting registration.
This innovative research represents an exciting advancement in the field of topological magnetic textures, and we look forward to seeing how this technology will be utilized in the future.
The research was supported by the National Science Foundation (OMA-1936221).
Fundamental physics and applications of skyrmions: A review
Magnetic skyrmions are tiny magnetic swirls that hold great potential in innovative electronic devices owing to their desirable properties of long-term stability, small size, and highly efficient controllability by various external stimuli. In this recently published review, we address the fundamental physics of the static, global and local dynamic properties of skyrmions and provide an overview of recent advances in computational models that utilize these unique properties. A discussion on the challenges lying ahead is also provided.
For more information, click here.
Research group observes the world’s largest tunnel magnetocapacitance of 426%
A research group, including Brown University Professor of Physics and Engineering Gang Xiao, has successfully observed the world’s largest tunnel magnetocapacitance (TMC) ratio and explained its mechanism. In addition to Xiao, the international collaborative was comprised of Kenta Sato, a second-year master’s student at Keio University’s Graduate School of Science and Technology in Japan, Hideo Kaiju, Associate Professor at Keio University’s Faculty of Science and Technology, and colleagues including Hiroaki Sukegawa, Principal Researcher at the National Institute for Materials Science in Japan.
TMC is a phenomenon in which capacitance (electrical capacitance, or the amount of electricity that a system can store) changes based on a magnetic field. This phenomenon is observed in textured magnetic tunnel junctions (MTJs) with a thin insulating layer between two magnetic layers. Until now, the largest observed TMC ratio, a figure-of-merit on magnetic sensitivity, has been 332%. In this study, researchers achieved the world’s largest TMC ratio of 426% by using an insulation tunneling layer and applying voltage biasing. Furthermore, they explained the mechanism behind this phenomenon using dielectric theory, which incorporates quantum mechanics and statistical theory.
These results pave the way for creating new capacitance-detecting, high-performance magnetic sensors and magnetic memory devices. They are also expected to be applied in next-generation Internet of Things (IoT) technology—a major driver of the Digital Age—and to make significant contributions to the acquisition, accumulation, and analysis of big data. In the future, these findings are expected to be put to practical use not only in the Information Technology/Information and Communication Technology (IT/ICT) field but also in a wide range of other fields, including environmental energy, healthcare, health sciences, transportation, agriculture, and manufacturing.
The research results were published online in Scientific Reports (via Springer Nature Group) on May 16, 2022.
Brown researchers use tiny magnetic swirls to generate true random numbers
Professor Gang Xiao’s Lab has developed a technique that can potentially generate millions of random digits per second by harnessing the behavior of skyrmions — tiny magnetic anomalies that arise in certain two-dimensional materials. Generating true random numbers is difficult, but they are extremely useful in cryptography and probabilistic computing. Read more.
Researchers develop ultra-sensitive device for detecting magnetic fields
The new magnetic sensor is inexpensive to make, works on minimal power and is 20 times more sensitive than many traditional sensors.
A team of Brown University physicists has developed a new type of compact, ultra-sensitive magnetometer. The new device could be useful in a variety of applications involving weak magnetic fields, the researchers say.
“Nearly everything around us generates a magnetic field — from our electronic devices to our beating hearts — and we can use those fields to gain information about all these systems,” said Gang Xiao, chair of the Brown Department of Physics and senior author of a paper describing the new device. “We have uncovered a class of sensors that are ultra-sensitive, but are also small, inexpensive to make and don’t use much power. We think there could be many potential applications for these new sensors.”
The new device is detailed in a paper published in Applied Physics Letters. Brown graduate student Yiou Zhang and postdoctoral researcher Kang Wang were the lead authors of the research.
A traditional way of sensing magnetic fields is through what’s known as the Hall effect. When a conducting material carrying current comes into contact with a magnetic field, the electrons in that current are deflected in a direction perpendicular to their flow. That creates a small perpendicular voltage, which can be used by Hall sensors to detect the presence of magnetic fields.
The new device makes use of a cousin to the Hall effect — known as the anomalous Hall effect (AHE) — which arises in ferromagnetic materials. While the Hall effect arises due to the charge of electrons, the AHE arises from electron spin, the tiny magnetic moment of each electron. The effect causes electrons with different spins to disperse in different directions, which gives rise to a small but detectable voltage.
The new device uses an ultra-thin ferromagnetic film made of cobalt, iron and boron atoms. The spins of the electrons prefer to be aligned in the plane of the film, a property called in-plane anisotropy. After the film is treated in a high-temperature furnace and under a strong magnetic field, the spins of the electrons develop a tendency to be oriented perpendicular to the film with what’s known as perpendicular anisotropy. When these two anisotropies have equal strength, electron spins can easily reorient themselves if the material comes into contact with an external magnetic field. That reorientation of electron spins is detectable through AHE voltage.
It doesn’t take a strong magnetic field to flip the spins in the film, which makes the device quite sensitive. In fact, it’s up to 20 times more sensitive than traditional Hall effect sensors, the researchers say.
Key to making the device work is the thickness of the cobalt-iron-boron film. A film that’s too thick requires stronger magnetic fields to reorient electron spins, which decreases sensitivity. If the film is too thin, electron spins could reorient on their own, which would cause the sensor to fail. The researchers found that the sweet spot for thickness was 0.9 nanometers, a thickness of about four or five atoms.
The researchers believe the device could have widespread applications. One example that could be helpful to medical doctors is in magnetic immunoassay, a technique that uses magnetism to look for pathogens in fluid samples.
“Because the device is very small, we can put thousands or even millions of sensors on one chip,” Zhang said. “That chip could test for many different things at one time in a single sample. That would make testing easier and less expensive.”
Another application could be as part of an ongoing project in Xiao’s lab supported by the National Science Foundation. Xiao and his colleagues are developing a magnetic camera that can make high-definition images of magnetic fields produced by quantum materials. Such a detailed magnetic profile would help researchers better understand the properties of these materials.
“Just like a regular camera, we want our magnetic camera to have as many pixels as possible,” Xiao said. “Each magnetic pixel in our camera is an individual magnetic sensor. The sensors need to be small and they can’t consume too much power, so this new sensor could be useful in our camera.”
The research was supported by the National Science Foundation (OMA-1936221).
Media Contact: Kevin Stacey
$2 million grant will support development of ‘magnetic camera’
A team of Brown University researchers will use a $2 million grant from the National Science Foundation to build a quantum mechanical magnetic camera, which will take snapshots of weak magnetic fields emanating from quantum materials. The camera will help researchers to understand the exotic materials that may one day be used in quantum computers and other quantum devices.
“Just as the camera on your phone has an array of photosensors that register light and create an image, our device will use magnetic sensors that can ‘see’ magnetic fields and make images or movies of magnetic patterns,” said Gang Xiao, chair of the physics department at Brown and principal investigator on the new grant. “We can learn a lot about quantum materials by observing in great detail the magnetic fields they produce, and that’s what this device will let us do.”
Quantum technologies make use of the often-peculiar behavior of individual subatomic particles. Harnessing that behavior could create computers than can perform calculations far beyond the reach of even the fastest of today’s supercomputers, sensors far more powerful than those used currently and potentially unbreakable encryption modes. Making these quantum tools work depends on a deeper understanding of how particles in quantum systems interact. Magnetic fields offer a window into those interactions, and the magnetic camera could potentially reveal the intricacies of those fields.
The challenge is making the device sensitive enough to register the ultra-weak magnetic signals generated by many quantum materials. To do that, the researchers will have to improve magnetic tunnel junctions (MTJs), tiny quantum mechanical sensors currently used to read information from computer hard disks. Xiao, who has studied MTJs and related nanoscale magnetic phenomena for years, will lead the team in investigating new materials for assembling MTJs and work with electronics experts to build specialized circuitry around them.
Joining Xiao on the team are three experts in quantum materials and phenomena: Vesna Mitrovic, Brad Marston and Kemp Plumb from Brown’s physics faculty. They’ll work with Professor of Engineering Alexander Zaslavsky and Senior Research Engineer William Patterson, both microelectronics experts.
The grant also includes funding for student entrepreneurship training, with an eye toward marketing the technology once it’s completed.
“The use for us is in exploring quantum materials, but if we’re able to scale this up, it could be useful for industry as well,” Xiao said. “A large enough camera could be useful in quality control for magnets used in a range of electronic devices. Similar devices could also be used in medical diagnostics to sense tiny shifts in magnetic fields generated by the heart or nervous system.”
Work on the project is scheduled to begin in January 2020.
To know more about the project, please visit Program Website.
Original article: https://www.brown.edu/news/2019-11-06/qmmc