wp-plugin-hostgator domain was triggered too early. This is usually an indicator for some code in the plugin or theme running too early. Translations should be loaded at the init action or later. Please see Debugging in WordPress for more information. (This message was added in version 6.7.0.) in /home4/scienrds/scienceandnerds/wp-includes/functions.php on line 6114ol-scrapes domain was triggered too early. This is usually an indicator for some code in the plugin or theme running too early. Translations should be loaded at the init action or later. Please see Debugging in WordPress for more information. (This message was added in version 6.7.0.) in /home4/scienrds/scienceandnerds/wp-includes/functions.php on line 6114Source:https:\/\/www.quantamagazine.org\/new-kind-of-magnetism-spotted-in-an-engineered-material-20240110\/#comments<\/a><\/br> All the magnets you have ever interacted with, such as the tchotchkes stuck to your refrigerator door, are magnetic for the same reason. But what if there were another, stranger way to make a material magnetic?<\/p>\n In 1966, the Japanese physicist Yosuke Nagaoka conceived of a type of magnetism<\/a> produced by a seemingly unnatural dance of electrons within a hypothetical material. Now, a team of physicists has spotted a version of Nagaoka\u2019s predictions playing out within an engineered material only six atoms thick.<\/p>\n The discovery, recently published in the journal Nature<\/em><\/a>, marks the latest advance in the five-decade hunt for Nagaoka ferromagnetism, in which a material magnetizes as the electrons within it minimize their kinetic energy, in contrast to traditional magnets. \u201cThat\u2019s why I\u2019m doing this kind of research: I get to learn things that we didn\u2019t know before, see things that we haven\u2019t seen before,\u201d said study co-author Livio Ciorciaro<\/a>, who completed the work while a doctoral candidate at the Swiss Federal Institute of Technology Zurich\u2019s Institute for Quantum Electronics.<\/p>\n In 2020, researchers created Nagaoka ferromagnetism<\/a> in a tiny system containing just three electrons, one of the smallest possible systems in which the phenomenon can occur. In the new study, Ciorciaro and his colleagues made it happen in an extended system \u2014 a patterned structure called a moir\u00e9 lattice that\u2019s formed from two nanometer-thin sheets.<\/p>\n This study \u201cis a really cool use of these moir\u00e9 lattices, which are relatively new,\u201d said Juan Pablo Dehollain<\/a>, a co-author of the 2020 study who completed the work at the Delft University of Technology. \u201cIt looks at this ferromagnetism in a kind of different way.\u201d<\/p>\n Traditional ferromagnetism arises because electrons don\u2019t like each other very much, so they have no desire to meet.<\/p>\n Imagine two electrons sitting next to each other. They\u2019ll repel each other because they both have negative electrical charges. Their lowest-energy state will find them far apart. And systems, as a rule, settle into their lowest-energy state.<\/p>\n According to quantum mechanics, electrons have a few other critical properties. First, they behave less like individual points and more like probabilistic clouds of mist. Second, they have a quantum property called spin, which is something like an internal magnet that can point up or down. And third, two electrons can\u2019t be in the same quantum state.<\/p>\n As a consequence, electrons that have the same spin will really want to get away from each other \u2014 if they\u2019re in the same place, with the same spin, they run the risk of occupying the same quantum state. Overlapping electrons with parallel spins stay slightly farther apart than they would otherwise.<\/p>\n In the presence of an external magnetic field, this phenomenon can be strong enough to cajole electron spins into lining up like little bar magnets, creating a macroscopic magnetic field within the material. In metals such as iron, these electron interactions, which are called exchange interactions, are so potent that the induced magnetization is permanent, as long as the metal isn\u2019t heated too much.<\/p>\n \u201cThe very reason that we have magnetism in our everyday lives is because of the strength of electron exchange interactions,\u201d said study co-author Ata\u00e7 \u0130mamo\u011flu<\/a>, a physicist also at the Institute for Quantum Electronics.<\/p>\n However, as Nagaoka theorized in the 1960s, exchange interactions may not be the only way to make a material magnetic. Nagaoka envisioned a square, two-dimensional lattice where every site on the lattice had just one electron. Then he worked out what would happen if you removed one of those electrons under certain conditions. As the lattice\u2019s remaining electrons interacted, the hole where the missing electron had been would skitter around the lattice.<\/p>\n In Nagaoka\u2019s scenario, the lattice\u2019s overall energy would be at its lowest when its electron spins were all aligned. Every electron configuration would look the same \u2014 as if the electrons were identical tiles in the world\u2019s most boring sliding tile puzzle<\/a>. These parallel spins, in turn, would render the material ferromagnetic.<\/p>\n \u0130mamo\u011flu and his colleagues had an inkling that they could create Nagaoka magnetism by experimenting with single-layer sheets of atoms that could be stacked together to form an intricate moir\u00e9 pattern (pronounced mwah-ray<\/em>). In atomically thin, layered materials, moir\u00e9 patterns can radically alter how electrons \u2014 and thus the materials \u2014 behave. For example, in 2018 the physicist Pablo Jarillo-Herrero and his colleagues demonstrated<\/a> that two-layer stacks of graphene gained the ability to superconduct when they offset the two layers with a twist.<\/p>\n Moir\u00e9 materials have since emerged as a compelling new system in which to study magnetism, slotted in alongside clouds of supercooled atoms and complex materials such as cuprates. \u201cMoir\u00e9 materials provide us a playground for, basically, synthesizing and studying many-body states of electrons,\u201d \u0130mamo\u011flu said.<\/p>\n The researchers started by synthesizing a material from monolayers of the semiconductors molybdenum diselenide and tungsten disulfide, which belong to a class of materials that past simulations<\/a> had implied could exhibit Nagaoka-style magnetism. They then applied weak magnetic fields of varying strengths to the moir\u00e9 material while tracking how many of the material\u2019s electron spins aligned with the fields.<\/p>\n The researchers then repeated these measurements while applying different voltages across the material, which changed how many electrons were in the moir\u00e9 lattice. They found something strange. The material was more prone to aligning with an external magnetic field \u2014 that is, to behaving more ferromagnetically \u2014 only when it had up to 50% more electrons than there were lattice sites. And when the lattice had fewer electrons than lattice sites, the researchers saw no signs of ferromagnetism. This was the opposite of what they would have expected to see if standard-issue Nagaoka ferromagnetism had been at work.<\/p>\n However the material was magnetizing, exchange interactions didn\u2019t seem to be driving it. But the simplest versions of Nagaoka\u2019s theory didn\u2019t fully explain its magnetic properties either.<\/p>\n Ultimately, it came down to movement. Electrons lower their kinetic energy by spreading out in space, which can cause the wave function describing one electron\u2019s quantum state to overlap with those of its neighbors, binding their fates together. In the team\u2019s material, once there were more electrons in the moir\u00e9 lattice than there were lattice sites, the material\u2019s energy decreased when the extra electrons delocalized like fog pumped across a Broadway stage. They then fleetingly paired up with electrons in the lattice to form two-electron combinations called doublons.<\/p>\n These itinerant extra electrons, and the doublons they kept forming, couldn\u2019t delocalize and spread out within the lattice unless the electrons in the surrounding lattice sites all had aligned spins. As the material relentlessly pursued its lowest-energy state, the end result was that doublons tended to create small, localized ferromagnetic regions. Up to a certain threshold, the more doublons there are coursing through a lattice, the more detectably ferromagnetic the material becomes.<\/p>\n Crucially, Nagaoka theorized that this effect would also work when a lattice had fewer electrons than lattice sites, which wasn\u2019t what the researchers saw. But according to the team\u2019s theoretical work \u2014 published in Physical Review Research<\/em><\/a> in June ahead of the experimental results \u2014 that difference comes down to the geometric quirks of the triangular lattice that they used versus the square one in Nagaoka\u2019s calculations.<\/p>\n You won\u2019t be able to affix kinetic ferromagnets to your fridge anytime soon, unless you do your cooking in one of the coldest places in the universe. Researchers evaluated the moir\u00e9 material for ferromagnetic behavior at a frosty 140 millikelvins.<\/p>\n To \u0130mamo\u011flu, the substance nonetheless reveals exciting new avenues for probing electrons\u2019 behavior in solids \u2014 and in applications that Nagaoka could have only dreamed of. In collaboration with Eugene Demler and Ivan Morera Navarro<\/a>, theoretical physicists at the Institute for Theoretical Physics, he wants to explore whether kinetic mechanisms like those at play within the moir\u00e9 material could be used to manipulate charged particles into pairing up, potentially pointing the way toward a new mechanism for superconductivity.<\/p>\n \u201cI\u2019m not saying that this is possible yet,\u201d he said. \u201cThat\u2019s where I want to go.\u201d<\/p>\n<\/div>\n <\/br><\/br><\/br><\/p>\n
\nNew Kind of Magnetism Spotted in an Engineered Material<\/br>
\n2024-01-12 21:58:29<\/br><\/p>\nWhen Your Parallel Spins Cause a Field to Begin<\/strong><\/h2>\n
When Two Grids With a Twist Make a Pattern Exist<\/strong><\/h2>\n
When Your Stuff Magnetized and You\u2019re Somewhat Surprised<\/strong><\/h2>\n
That\u2019s a-Moir\u00e9<\/strong><\/h2>\n