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Revealing the thermal heat dance of magnetic domains

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Everyone knows that holding two magnets together will lead to one of two results: they stick together, or they push each other apart. From this perspective, magnetism seems simple, but scientists have struggled for decades to really understand how magnetism behaves on the smallest scales. On the near-atomic level, magnetism is made of many ever-shifting kingdoms — called magnetic domains — that create the magnetic properties of the material. While scientists know these domains exist, they are still looking for the reasons behind this behavior.

Now, a collaboration lead by scientists from the U.S. Department of Energy’s Brookhaven National Laboratory, Helmholtz-Zentrum Berlin (HZB), the Massachusetts Institute of Technology (MIT), and the Max Born Institute (MBI) published a study in Nature in which they used a novel analysis technique — called coherent correlation imaging (CCI) — to image the evolution of magnetic domains in time and space without any previous knowledge. The scientists could not see the “dance of the domains” during the measurement but only afterward, when they used the recorded data to “rewind the tape.”

The “movie” of the domains shows how the boundaries of these domains shift back and forth in some areas but stay constant in others. The researchers attribute this behavior to a property of the material called “pinning.” While pinning is a known property of magnetic materials, the team could directly image for the first time how a network of pinning sites affects the motion of interconnected domain walls.

“Many details about the changes in magnetic materials are only accessible through direct imaging, which we couldn’t do until now. It’s basically a dream come true for studying magnetic motion in materials,” said Wen Hu, scientist at the National Synchrotron Light Source II (NSLS-II) and co-corresponding author of the study.

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The researchers expect CCI to help unlock other properties of the microcosm of magnetism — such as degrees of freedom or hidden symmetries — that previously weren’t accessible through other techniques. CCI’s usefulness also represents a breakthrough beyond magnetic materials since the technique can be transferred to different measurement techniques and research areas. One area that might benefit the most from understanding the movement of magnetic domains on the nanoscale (one nanometer is 0.000000038 inches!) is novel computing. Novel memory technology could leverage special magnetic domains called “skyrmions.”

“Skyrmions are interesting for artificial intelligence computing because they possess a property that is similar to our short-term memory,” said Felix Büttner, group leader at Helmholtz-Zentrum Berlin, professor at the University of Augsburg and co-corresponding of the study. “In current computing architectures everything is linear, which means that the memory is separated from the processor. This is not an issue for most applications but, for example, it makes speech recognition difficult. In speech recognition, the computing part only processes the incoming words, but doesn’t remember what has been said previously. In addition, sending that information back from the memory takes a lot of energy. By using skyrmions, we may be able to harness their short-term memory in some way and avoid these issues.”

However, before engineers and scientists can develop technology that uses this feature, they first need to understand how to manipulate skyrmions and other magnetic domains. This was the intention when the collaboration between NSLS-II, Geoffrey Beach’s group at MIT, and MBI formed. They wanted to investigate how skyrmions in their magnetic devices reacted to external stimuli, specifically in an external magnetic field. HZB joined the collaboration when Büttner moved from MIT to Berlin.

“In 2018, we had measurement time at the Coherent Soft X-ray Scattering (CSX) beamline at NSLS-II; however, the experimental chamber we wanted to use wasn’t ready. That meant we didn’t have the external magnetic field, but we had a back-up plan for studying the thermal motion,” said Hu, who is part of the CSX beamline team.

Büttner added, “I expected this experiment would be another demonstration experiment but nothing more. To be honest, I was surprised we saw thermal motion at all. We studied the same device at room temperature and barely saw any thermal motion. This time we studied it at 310 Kelvin, which is about 98 Fahrenheit, and we saw so much more. That was surprising! And it was just the beginning.”

How a back-up plan leads to hidden insights

In their experiment, the team used coherent x-rays from the CSX beamline to take a series of snapshots of the magnetic domains. CSX is part of the advanced suite of research tools available at NSLS-II for studying materials. The research team used the beamline in a holography setup to take the images. In most holography experiments, scientists take one image every three to four seconds, however, the fast detector at the CSX beamline allowed the team to take up to 100 images per second.

“After the measurement, we started a normal data analysis by adding up 200 images. Once we did this, we realized that the system changed much faster than we expected. The temperature really influenced the physics in the sample,” said Christopher Klose, PhD student at MBI and first author of the study. “That was a real surprise and the beginning of us developing our post-processing technique — coherent correlation imaging (CCI) — so that we could resolve this fast movement.”

After this initial realization, the team decided to dig deeper into the data. They knew that the details about the domain movements were encoded in their data. While there was no existing data analysis technique to solve their problem, they were able to find algorithms that could be adapted. Over the course of three years, the team developed the new algorithm that powers the novel CCI technique.

“There were a lot of challenges. To develop CCI, we combined known correlation function analysis from x-ray photon correlation spectroscopy (XPCS) with holography, which is an imaging technique. One issue was that the holography data was not suited for XPCS analysis,” said Klose.

When x-rays hit the samples in these experiments, they scatter both on the magnetic domains and a holographic mask that defines the field of view. The detector records all the scattered x-rays regardless of their origin. But the team is only interested in magnetic scattering. So, they needed to clean up the data before they could calculate the correlation functions.

“Once we had the correlation function, we could compare all those frames to each other to find similar ones. That also required a new algorithm because we had almost 30,000 frames to sort through,” continued Klose.

This challenge required an algorithm that could catalog the states of the domains for each frame. This algorithm would be a real game-changer for this task because it would be able to sort these states in ways no human could achieve.

How pinning shapes the magnetic landscape

After the team had sorted through their data using CCI, they went to work on the interpretation. The reconstructed images showed black and white domains scattered across their device. But some of these borders, or domain walls, shifted back and forth between the frames, while others mostly stayed put. The question: what were the researchers seeing and what did this mean for skyrmions and magnetic domains?

“Skyrmions are small spherical objects, comparable to balls on a pool table. In our case, thermal energy makes them wander around the table. Now, if the pool table has pinning, the surface isn’t smooth but instead is a hilly landscape. We have two kinds of pinning sites: attractive ones and repulsive ones. The first ones are valleys, and the second ones are hills. In that case, the skyrmions would rest in the “attractive” valleys. If they wanted to move around, they would need to overcome the slopes of the “repulsive” hills,” said Büttner.

The researchers found that domain walls behave like rubber bands. They can be pinned down and then oscillate back and forth like a guitar string. While attractive sites can accommodate domain walls, repulsive sites inhibit the movement of domain walls. A domain wall would need to be lifted over the repulsive site. It cannot wander through it. This explains why the scientists saw some domain walls shift constantly, while other barely moved. The latter ones were surrounded by repulsive sites.

“CCI gave us the tool to see this movement over time. Basically, we could make a little movie on how these domains shift. This experiment allowed us to see this kind of fluctuating behavior and its cause for the first time,” said Hu. “We didn’t expect that this collaboration would lead to the invention of a new technique that would broadly benefit other users and researchers studying dynamics.”

Büttner added, “We needed almost a year to fully understand the physics we had found and develop an explanation for the dynamics that we saw. In hindsight, the experiment itself was the easiest part of it all. The real work was the technique development and then the physics explanation.”

The researchers agreed that one key ingredient for this breakthrough was the diverse team of experts they had assembled for this task. They hope that many other research groups will benefit from CCI. While they prepare for applying CCI to a broader range of previously inaccessible dynamics as well as expanding the technique to other x-ray sources, they’re also working on implementing machine learning to make the CCI analysis less manual and more accessible by an even broader community.

The team for this work consisted of Christopher Klose, Michael Schneider, Stefan Eisebitt and Bastian Pfau from the Max Born Institute, Felix Büttner and Riccardo Battistelli from the Helmholtz-Zentrum Berlin, Wen Hu, Claudio Mazzoli, Andi Barbour and Stuart B. Wilkins from the National Synchrotron Light Source II at Brookhaven National Laboratory, Kai Litzius, Ivan Lemesh, Jason M. Bartell, Mantao Huang and Geoffrey S.D. Beach from the Massachusetts Institute of Technology, Christian M. Günther from the Technische Universität Berlin.

NSLS-II is a U.S. Department of Energy (DOE) Office of Science user facility located at DOE’S Brookhaven National Laboratory.

This work was supported by the DOE Office of Science.

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Asteroid 2023 BU just passed a few thousand kilometres from Earth. Here’s why that’s exciting – The Tribune India

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Perth (Australia), January 28

There are hundreds of millions of asteroids in our Solar System, which means new asteroids are discovered quite frequently. It also means close encounters between asteroids and Earth are fairly common.

Some of these close encounters end up with the asteroid impacting Earth, occasionally with severe consequences.

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A recently discovered asteroid, named 2023 BU, has made the news because today it passed very close to Earth.

Discovered on January 21 by amateur astronomer Gennadiy Borisov in Crimea, 2023 BU passed only about 3,600 km from the surface of Earth (near the southern tip of South America) six days later on January 27.

That distance is just slightly farther than the distance between Perth and Sydney and is only about 1 per cent the distance between Earth and our Moon.

The asteroid also passed through the region of space that contains a significant proportion of the human-made satellites orbiting Earth.

All this makes 2023 BU the fourth-closest known asteroid encounter with Earth, ignoring those that have impacted the planet or our atmosphere.

How does 2023 BU rate as an asteroid and a threat?

2023 BU is unremarkable, other than that it passed so close to Earth. The diameter of the asteroid is estimated to be just 4–8 metres, which is on the small end of the range of asteroid sizes.

There are likely hundreds of millions of such objects in our Solar System, and it is possible 2023 BU has come close to Earth many times before over the millennia. Until now, we have been oblivious to the fact.

In context, on average a 4-metre-diameter asteroid will impact Earth every year and an 8-metre-diameter asteroid every five years or so                  

Asteroids of this size pose little risk to life on Earth when they hit because they largely break up in the atmosphere. They produce spectacular fireballs, and some of the asteroids may make it to the ground as meteorites.

Now that 2023 BU has been discovered, its orbit around the Sun can be estimated and future visits to Earth predicted. It is estimated there is a 1 in 10,000 chance  2023 BU will impact Earth sometime between 2077 and 2123.

So, we have little to fear from 2023 BU or any of the many millions of similar objects in the Solar System.

Asteroids need to be greater than 25 metres in diameter to pose any significant risk to life in a collision with Earth; to challenge the existence of civilisation, they’d need to be at least a kilometre in diameter.

It is estimated there are fewer than 1,000 such asteroids in the Solar System and could impact Earth every 5,00,000 years. We know about more than 95 per cent of these objects.

Will there be more close asteroid passes?

2023 BU was the fourth closest pass by an asteroid ever recorded. The three closer passes were by very small asteroids discovered in 2020 and 2021 (2021 UA, 2020 QG and 2020 VT).

Asteroid 2023 BU and countless other asteroids have passed very close to Earth during the nearly five billion years of the Solar System’s existence, and this situation will continue into the future.

What has changed in recent years is our ability to detect asteroids of this size, such that any threats can be characterised. That an object roughly five metres in size can be detected many thousands of kilometres away by a very dedicated amateur astronomer shows that the technology for making significant astronomical discoveries is within reach of the general public. This is very exciting.

Amateurs and professionals can together continue to discover and categorise objects, so threat analyses can be done. Another very exciting recent development came last year, by the Double Asteroid Redirection Test (DART) mission, which successfully collided a spacecraft into an asteroid and changed its direction.

DART makes plausible the concept of redirecting an asteroid away from a collision course with Earth if a threat analysis identifies a serious risk with enough warning. (The Conversation)

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An SUV-sized asteroid zoom by Earth in close shave flyby in this time-lapse video

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Asteroid 2023 BU zipped past Earth Thursday night (Jan. 26) to the delight of amateur astronomers worldwide. For skywatchers without access to a telescope or those who had their view hampered by bad weather, luckily the Italy-based Virtual Telescope Project was there to observe the event and livestream the whole thing for free.

The Virtual Telescope is a robotic telescope operated by Italian amateur astronomer Gianluca Masi near Rome, Italy. As 2023 BU hurtled toward Earth, the telescope was able to track the rock through a gap in the clouds when it was about 13,670 miles (22,000 kilometers) from the closest point on Earth’s surface (about the altitude of the GPS navigation satellite constellation) and 22,990 miles (37,000 km) from the Virtual Telescope.

Masi, who shared an hour-long webcast of the observations on the Virtual Telescope website, wasn’t able to capture the closest approach as clouds rolled in, however. Nonetheless, the Virtual Telescope Project was able to get a good look at the car-sized rock, seen in time-lapse above.

 

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The Italy-based Virtual Telescope captured asteroid 2023 BU shortly before its closest approach to Earth. (Image credit: The Virtual Telescope Project)

The rock, discovered less than a week ago on Saturday (Jan. 21), passed above the southern tip of South America at 7:27 p.m. EST on Thursday Jan. 26 (0027 GMT on Jan. 27), at a distance of only 2,240 miles (3,600 km) at its closest point to Earth’s surface.

This close approach makes 2023 BU the fourth nearest asteroid ever observed from Earth, with the exception of five space rocks that were detected before diving into Earth’s atmosphere.

Only 11.5 to 28 feet wide (3.5 to 8.5 meters), 2023 BU posed no danger to the planet. If the trajectories of the two bodies had intersected, the asteroid would mostly have burned up in the atmosphere with only small fragments possibly falling to the ground as meteorites.

In the videos and images shared by Masi, the asteroid is seen as a small bright dot in the center of the frame, while the longer, brighter lines are the surrounding stars. In reality, of course, it was the asteroid that was moving with respect to Earth, traveling at a speed of 21,000 mph (33,800 km/h) with respect to Earth. As Masi’s computerized telescope tracked its positionthe rock appeared stationary in the images while rendering the stars as these moving streaks.

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The gravitational kick that 2023 BU received during its encounter with Earth will alter the shape of its orbit around the sun. Previously, the space rock followed a rather circular orbit, completing one lap around the sun in 359 days. From now on, BU 2023 will travel through the inner solar system on a more elliptical path, venturing half way toward Mars at the farthest point of its orbit. This alteration will add 66 days to BU 2023’s orbital period.

The asteroid was discovered by famed Crimea-based astronomer and astrophotographer Gennadiy Borisov, the same man who in 2018 found the first interstellar comet, which now bears his name, Borisov.

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Green comet zooming our way, last visited 50,000 years ago

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This photo provided by Dan Bartlett shows comet C/2022 E3 (ZTF) on Dec. 19, 2022. It last visited during Neanderthal times, according to NASA. It is expected to come within 26 million miles (42 million kilometers) of Earth on Feb. 1, 2023, before speeding away again, unlikely to return for millions of years. Credit: Dan Bartlett via AP

A comet is streaking back our way after 50,000 years.

The dirty snowball last visited during Neanderthal times, according to NASA. It will come within 26 million miles (42 million kilometers) of Earth Wednesday before speeding away again, unlikely to return for millions of years.

So do look up, contrary to the title of the killer- movie “Don’t Look Up.”

Discovered less than a year ago, this harmless green comet already is visible in the northern night sky with binoculars and small telescopes, and possibly the naked eye in the darkest corners of the Northern Hemisphere. It’s expected to brighten as it draws closer and rises higher over the horizon through the end of January, best seen in the predawn hours. By Feb. 10, it will be near Mars, a good landmark.

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Skygazers in the Southern Hemisphere will have to wait until next month for a glimpse.

While plenty of comets have graced the sky over the past year, “this one seems probably a little bit bigger and therefore a little bit brighter and it’s coming a little bit closer to the Earth’s orbit,” said NASA’s comet and asteroid-tracking guru, Paul Chodas.

Green from all the carbon in the gas cloud, or coma, surrounding the nucleus, this long-period comet was discovered last March by astronomers using the Zwicky Transient Facility, a wide field camera at Caltech’s Palomar Observatory. That explains its official, cumbersome name: comet C/2022 E3 (ZTF).

On Wednesday, it will hurtle between the orbits of Earth and Mars at a relative speed of 128,500 mph (207,000 kilometers). Its nucleus is thought to be about a mile (1.6 kilometers) across, with its tails extending millions of miles (kilometers).

The comet isn’t expected to be nearly as bright as Neowise in 2020, or Hale-Bopp and Hyakutake in the mid to late 1990s.

Green comet zooming our way, last visited 50,000 years ago
This photo provided by Dan Bartlett shows comet C/2022 E3 (ZTF) on Dec. 19, 2022. It last visited during Neanderthal times, according to NASA. It is expected to come within 26 million miles (42 million kilometers) of Earth on Feb. 1, 2023, before speeding away again, unlikely to return for millions of years. Credit: Dan Bartlett via AP

But “it will be bright by virtue of its close Earth passage … which allows scientists to do more experiments and the public to be able to see a beautiful comet,” University of Hawaii astronomer Karen Meech said in an email.

Scientists are confident in their orbital calculations putting the comet’s last swing through the ‘s planetary neighborhood at 50,000 years ago. But they don’t know how close it came to Earth or whether it was even visible to the Neanderthals, said Chodas, director of the Center for Near Earth Object Studies at NASA’s Jet Propulsion Laboratory in California.

When it returns, though, is tougher to judge.

Every time the comet skirts the sun and planets, their gravitational tugs alter the iceball’s path ever so slightly, leading to major course changes over time. Another wild card: jets of dust and gas streaming off the comet as it heats up near the sun.

“We don’t really know exactly how much they are pushing this comet around,” Chodas said.

The comet—a time capsule from the emerging solar system 4.5 billion years ago—came from what’s known as the Oort Cloud well beyond Pluto. This deep-freeze haven for comets is believed to stretch more than one-quarter of the way to the next star.

While comet ZTF originated in our solar system, we can’t be sure it will stay there, Chodas said. If it gets booted out of the solar system, it will never return, he added.

Don’t fret if you miss it.

“In the comet business, you just wait for the next one because there are dozens of these,” Chodas said. “And the next one might be bigger, might be brighter, might be closer.”

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