Tag Archives: magnet

China builds the world’s first artificial moon

Chinese scientists have built an ‘artificial moon’ possessing lunar-like gravity to help them prepare astronauts for future exploration missions. The structure uses a powerful magnetic field to produce the celestial landscape — an approach inspired by experiments once used to levitate a frog.

The key component is a vacuum chamber that houses an artificial moon measuring 60cm (about 2 feet) in diameter. Image credits: Li Ruilin, China University of Mining and Technology

Preparing to colonize the moon

Simulating low gravity on Earth is a complex process. Current techniques require either flying a plane that enters a free fall and then climbs back up again or jumping off a drop tower — but these both last mere minutes. With the new invention, the magnetic field can be switched on or off as needed, producing no gravity, lunar gravity, or earth-level gravity instantly. It is also strong enough to magnetize and levitate other objects against the gravitational force for as long as needed.

All of this means that scientists will be able to test equipment in the extreme simulated environment to prevent costly mistakes. This is beneficial as problems can arise in missions due to the lack of atmosphere on the moon, meaning the temperature changes quickly and dramatically. And in low gravity, rocks and dust may behave in a completely different way than on Earth – as they are more loosely bound to each other.

Engineers from the China University of Mining and Technology built the facility (which they plan to launch in the coming months) in the eastern city of Xuzhou, in Jiangsu province. A vacuum chamber, containing no air, houses a mini “moon” measuring 60cm (about 2 feet) in diameter at its heart. The artificial landscape consists of rocks and dust as light as those found on the lunar surface-where gravity is about one-sixth as powerful as that on Earth–due to powerful magnets that levitate the room above the ground. They plan to test a host of technologies whose primary purpose is to perform tasks and build structures on the surface of the Earth’s only natural satellite.

Group leader Li Ruilin from the China University of Mining and Technology says it’s the “first of its kind in the world” that will take lunar simulation to a whole new level. Adding that their artificial moon makes gravity “disappear.” For “as long as you want,” he adds.

In an interview with the South China Morning Post, the team explains that some experiments take just a few seconds, such as an impact test. Meanwhile, others like creep testing (where the amount a material deforms under stress is measured) can take several days.

Li said astronauts could also use it to determine whether 3D printing structures on the surface is possible rather than deploying heavy equipment they can’t use on the mission. He continues:

“Some experiments conducted in the simulated environment can also give us some important clues, such as where to look for water trapped under the surface.”

It could also help assess whether a permanent human settlement could be built there, including issues like how well the surface traps heat.

From amphibians to artificial celestial bodies

The group explains that the idea originates from Russian-born UK-based physicist Andre Geim’s experiments which saw him levitate a frog with a magnet – that gained him a satirical Ig Nobel Prize in 2000, which celebrates science that “first makes people laugh, and then think.” Geim also won a Nobel Prize in Physics in 2010 for his work on graphene.

The foundation of his work involves a phenomenon known as diamagnetic levitation, where scientists apply an external magnetic force to any material. In turn, this field induces a weak repulsion between the object and the magnets, causing it to drift away from them and ‘float’ in midair.

For this to happen, the magnetic force must be strong enough to ‘magnetize’ the atoms that make up a material. Essentially, the atoms inside the object (or frog) acts as tiny magnets, subject to the magnetic force existing around them. If the magnet is powerful enough, it will change the direction of the electrons revolving around the atom’s nuclei, allowing them to produce a magnetic field to repulse the magnets.

Diamagnetic levitation of a tiny horse. Image credits: Pieter Kuiper / Wiki Commons.

Different substances on Earth have varying degrees of diamagnetism which affect their ability to levitate under a magnetic field; adding a vacuum, as was done here, allowed the researchers to produce an isolated chamber that mimics a microgravity environment.

However, simulating the harsh lunar environment was no easy task as the magnetic force needed is so strong it could tear apart components such as superconducting wires. It also affected the many metallic parts necessary for the vacuum chamber, which do not function properly near a powerful magnet.

To counteract this, the team came up with several technical innovations, including simulating lunar dust that could float a lot easier in the magnetic field and replacing steel with aluminum in many of the critical components.

The new space race

This breakthrough signals China’s intent to take first place in the international space race. That includes its lunar exploration program (named after the mythical moon goddess Chang’e), whose recent missions include landing a rover on the dark side of the moon in 2019 and 2020 that saw rock samples brought back to Earth for the first time in over 40 years.

Next, China wants to establish a joint lunar research base with Russia, which could start as soon as 2027.  

The new simulator will help China better prepare for its future space missions. For instance, the Chang’e 5 mission returned with far fewer rock samples than planned in December 2020, as the drill hit unexpected resistance. Previous missions led by Russia and the US have also had related issues.

Experiments conducted on a smaller prototype simulator suggested drill resistance on the moon could be much higher than predicted by purely computational models, according to a study by the Xuzhou team published in the Journal of China University of Mining and Technology. The authors hope this paper will enable space engineers across the globe (and in the future, the moon) to alter their equipment before launching multi-billion dollar missions.

The team is adamant that the facility will be open to researchers worldwide, and that includes Geim. “We definitely welcome Professor Geim to come and share more great ideas with us,” Li said.

A 2-D layer of chromium triiodide atoms -- the first single-sheet magnet in the world. Credit: Efrén Navarro Moratalla.

Presenting the first 2D magnet: it will allow scientists to make previously impossible experiments

Two decades ago, the notion of actually working in applied science with 2D materials was seen as a pipedream. But that all changed after graphene was first forged in Manchester, UK, in 2004. Since then, scientists have demonstrated one-atom-thick semiconductors, insulators, even superconductors. Now, a pair of talented physicists has completed the spectrum by adding magnets to the 2D family.

A 2-D layer of chromium triiodide atoms -- the first single-sheet magnet in the world. Credit: Efrén Navarro Moratalla.

A 2-D layer of chromium triiodide atoms — the first single-sheet magnet in the world. Credit: Efrén Navarro Moratalla.

Up until this breakthrough study, scientists weren’t sure a 2D magnet was even possible. Here we are, though.

The discovery could ultimately lead to novel storage devices that work fundamentally different. Quantum computers might also benefit from this. Most of all, however, scientists working in fundamental physics will have their work cut out for them many years ahead as they now have the chance to perform experiments previously thought impossible.  “It’s a matter of principle — there is a big thing missing,” Jarillo-Herrero told Nature.

Previously, the thinnest magnets were demonstrated by a group of Chinese researchers who worked with a crystal made of chromium, germanium, and tellurium. However, when the crystal was stripped to a single-atom layer, it lost its magnetic properties so not a real 2D magnet at all.

To build one, Xu and Jarilo-Herrero literally stripped a chromium triiodide (Crl3) crystal until all was left was a single-atom-thick layer. The reason why they choose this material was that it’s made of stacked sheets that can be separated easily using the so-called “Scotch tape method”, which literally means using adhesive tape to peel off layers off the larger, 3-D crystal form. The technique has been used to make graphene for some time. Secondly, chromium triiodide is ferromagnet (permanent magnet) and is also anisotropic, meaning it has physical properties which vary when measured in different directions. In our case, the material’s electrons spin perpendicular to the plane of the crystal. These were very good hints that suggested chromium triiodide could work as a 2D magnet.

By this point, it’s maybe important to mention what 2D actually means. It’s not the same as in, say, math where 2D means a completely flat plane. After all, this material is made of atoms and an atom is essentially 3D. Functionally, however, the atoms within the monolayer material are considered 2D because the electrons are confined to the atomic sheet, like pieces on a chessboard.

Layer by layer, the two physicists stripped chromium triiodide until it became 2D and low and behold it was magnetic. Moreover, this property arises at a relatively low temperature when working in the atomic domain: -228 degrees Celsius.

Top-view depiction of a CrI3 lattice. Cr atoms are in grey, I atoms are in purple. Credit: Efren Navarro-Moratalla.

Top-view depiction of a CrI3 lattice. Cr atoms are in grey, I atoms are in purple. Credit: Efren Navarro-Moratalla.

Another interesting quirk was that when the material was comprised of two-layered sheets, it stopped being magnetic. They tested it by shining polarized light on the material, which returns a distinct signature in response to ferromagnetism. Adding another third sheet turned the material back into a ferromagnet and remained ferromagnetic when the fourth layer was added as well. The researchers are still investing why.

“2D monolayers alone offer exciting opportunities to study the drastic and precise electrical control of magnetic properties, which has been a challenge to realize using their 3D bulk crystals,” says Xiaodong Xu, lead author of the study, in a statement. “But an even greater opportunity can arise when you stack monolayers with different physical properties together. There, you can get even more exotic phenomena not seen in the monolayer alone or in the 3D bulk crystal.”

This is the culmination of more than five decades worth of searching for an ultrathin magnet. We now got more than anyone bargained for: a 2D magnet. But to be really useful, physicists would like to find a 2D ferromagnet that works at room temperature and ambient conditions, like in the presence of oxygen for instance. Jarillo-Herrero and Xu are currently exploring other magnets in chromium triiodide’s chemical family for clues.

Meanwhile, they also want to layer this 2D magnet with a 2D superconductor to see what happens.

“Does the superconductor destroy the ferromagnet, or does the ferromagnet destroy the superconductor?” Jarillo-Herrero told Nature. “It was just not possible to do this experiment before.”

“Heterostructures hold the greatest promise of realizing new applications in computing, database storage, communications and other applications we cannot even fathom yet,” said Xu.

The findings were reported in the journal Nature.

Czech researchers turn graphene sheets into the first stable non-metallic magnets

Researchers have created the first stable non-metal magnet ever by treating graphene layers with non-metallic elements.

Image credits Wikimedia / AlexanderAlUS.

A team from the Regional Center of Advanced Technologies and Materials at the Palacky University, Olomouc, Czech Republic, announced that they have created the first non-metal magnet that can maintain its properties at room temperature. The process requires no metals — the team created their magnet by treating graphene layers with non-metallic elements such as fluorine, hydrogen, or oxygen.

“For several years, we have suspected that the path to magnetic carbon could involve graphene — a single two-dimensional layer of carbon atoms,” lead researcher Radek Zbořil, director of the RCATM, in a press release.

“[Through the process] we were able to create a new source of magnetic moments that communicate with each other even at room temperature. This discovery is seen as a huge advancement in the capabilities of organic magnets.”

They’ve also developed the theoretical framework to explain why their unique chemical treatment creates magnets without any metal.

“In metallic systems, magnetic phenomena result from the behavior of electrons in the atomic structure of metals,” explained co-author Michal Otyepka.

“In the organic magnets [i.e. the graphene ones] that we have developed, the magnetic features emerge from the behavior of non-metallic chemical radicals that carry free electrons.”

Graphene is already getting a lot of attention for its unique electrical and physical properties as well as electrical conductivity. Adding magnetism to the list of it can do opens up a whole new range of possibilities for a material that is in essence sheet carbon you can cook make from soy.

“Such magnetic graphene-based materials have potential applications in the fields of spintronics and electronics, but also in medicine for targeted drug delivery and for separating molecules using external magnetic fields,” the team adds.

The full paper “Room temperature organic magnets derived from sp3 functionalized graphene” has been published in the journal Nature.

High-field magnet system, capable of creating fields as strong as 250,000 times the earth's magnetic field. The experiment was lowered into such a system. Credit: Jason Krizan

Frustrated magnets really do exhibit Hall’s effect, but only near absolute zero temperature

Settling a long debate, Princeton University researchers found that a class of materials called frustrated magnets – called so because they’re not magnetic, though they should be – can exhibit the Hall effect. This happens only at very, very low temperatures close to absolute zero, when physics transcends familiar, classical behavior into the quantum domain. First  observed in 1879 by E.H. Hall, the effect describes how current deflects to one side of the ribbon when an electrically charged conductor is subjected to a magnetic field. It has since been exploited for use in in sensors for devices such as computer printers and automobile anti-lock braking systems. The current study is particularly important since it may reveal more about how transmission of frictionless electricity works (superconductivity), while also offering hints and clues that may help researchers devise the oh-so heralded quantum computers of the future.

High-field magnet system, capable of creating fields as strong as 250,000 times the earth's magnetic field. The experiment was lowered into such a system. Credit: Jason Krizan

High-field magnet system, capable of creating fields as strong as 250,000 times the earth’s magnetic field. The experiment was lowered into such a system. Credit: Jason Krizan

Because the Hall Effect happens in charge-carrying particles, most physicists thought it would be impossible to see such behavior in non-charged, or neutral, particles like those in frustrated magnets.

“To talk about the Hall Effect for neutral particles is an oxymoron, a crazy idea,” said N. Phuan Ong, Princeton’s Eugene Higgins Professor of Physics.

Previous theoretical research, however, posited that the Hall effect should occur in the neutral particles in frustrated magnets might bend to the Hall rule under extremely cold conditions, near absolute zero. To settle the debate, a team of Princeton physicists and chemists made their own pyrochlore crystals, a class of materials that contain magnetic moments that, at very low temperatures near absolute zero, should line up in an orderly manner so that all of their “spins,” a quantum-mechanical property, point in the same direction. Instead, experiments have found that the spins point in random directions. Quite frustrating, indeed.

“These materials are very interesting because theorists think the tendency for spins to align is still there, but, due to a concept called geometric frustration, the spins are entangled but not ordered,” Ong said

Gold electrodes were attached to each end of the  thin, flat transparent slabs of pyrochlore and drove a heat current through the crystals. At such low temperatures, this heat current is analogous to the electric current in the ordinary Hall Effect experiment. The a magnetic field was driven in a direction perpendicular to the heat current. To their surprise, the heat current was deflected to one side of the current. To make sure they weren’t seeing something else, the researchers reconfigured the experiment to reverse the heat current. This time around, the heat current was deflected to the other side, just as Hall predicted. Findings appeared in Science.

“All of us were very surprised because we work and play in the classical, non-quantum world,” Ong said. “Quantum behavior can seem very strange, and this is one example where something that shouldn’t happen is really there. It really exists.”

Experiments such as these are essential to expanding our understanding of how superconductive materials work, especially “high-temperature” superconductors like cuprates which work at temperatures well beyond absolute zero. Previously, ZME Science reported how spin manipulation might one day help manufacture room-temperature superconductors, which would be extremely consequential for the way energy is carried from transmission cables to microchips.

 

Science ABC: the eddy currents, and the coolest video you’ll see today

Eddy currents are electrical phenomena that take place when a conductor is exposed to an oscilation of the magnetic field due to the relative motion of the field source and conductor; rewind. You have a conductor, say a copper tube, and a magnet. One moves relative to the other and you’ve got current (basically a circulating flow of electrons). These currents also generate heat as well as electromagnetism, and can be harnessed. I won’t go into additional details which you can find on wikipedia or physling, but instead, I’m gonna show you this video, which is just another example of how amazing physics really is.