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Here\u2019s what you\u2019ll learn when you read this story:<\/p>\n
Today, scientists don\u2019t discover \u201claws\u201d but instead perfect theories, always aware that there\u2019s more to learn.<\/p>\n
A new study shows why centuries-old \u201claws\u201d need some tweaking, as a 300-year-old law of friction fails to predict interactions between two magnetic materials.<\/p>\n
Understanding this physics-based exception could help improve micro- and nano-devices that rely on magnetism to function.<\/p>\n
Today, scientists aren\u2019t in the habit of creating \u201claws.\u201d Sure, we still refer to scientific breakthroughs of centuries past as \u201claws,\u201d chief among them being Isaac Newton\u2019s laws of motion, among many others. But as science has matured, we\u2019ve come to learn that these laws are far from inviolable<\/a>. Newton\u2019s laws of motion, for example, break down at extreme scales, which is where Albert Einstein\u2019s general theory of relativity comes in.<\/p>\n Now a team of scientists at the University of Konstanz in Germany have once again proven why the word \u201ctheory,\u201d which allows some flexibility for future discoveries, replaced \u201claws\u201d in today\u2019s scientific parlance. The law in question is Amontons\u2019 first law of friction<\/a>. Postulated by French physicist Guillaume Amontons<\/a> in the treatise De la r\u00e9sistance caus\u00e9e dans les machines in 1699, the idea is pretty intuitive: \u201cThe force of friction is directly proportional to the applied load.\u201d This simply means that a heavier object (say a couch) is going to exert higher friction than something lighter (a chair). This is because tiny deformations in materials increase in contact under heavier loads, which in effect enhances friction.<\/p>\n But in a new study published in the journal Nature Materials<\/a>, researchers discovered that this law breaks down when considering magnetic<\/a> materials. In an experiment, the authors used a two-dimensional array of freely rotating magnetic elements above a second magnetic layer. Although these materials never come into contact, there is measurable magnetic friction between the two.<\/p>\n \u201cBy changing the distance between the magnetic layers, we could drive the system into a regime of competing interactions where the rotors constantly reorganize as they slide,\u201d said<\/a> Hong Kong University of Science and Technology\u2019s Hongri Gu, who co-authored this research while at the University of Konstanz.<\/p>\n What the researchers discovered is that at close and far distances, friction was at its weakest, but it actually increased at intermediate distances. That\u2019s because at these medium distances, competing interactions take over. For example, in the top magnetic layer, magnetic moments point in parallel<\/a> but opposite directions, which is known as \u201cantiparallel alignment,\u201d while the bottom layer flows into a same-direction parallel alignment. This unstable configuration causes increased magnetic friction as the materials are forced to constantly switch between parallel and antiparallel states.<\/p>\n \u201cWhat is remarkable is that friction here arises entirely from internal reorganization,\u201d University of Konstanz\u2019s Clemens Bechinger, supervisor on the project, said in a press statement. \u201cThere is no wear<\/a>, no surface roughness, and no direct contact. Dissipation is generated solely by collective magnetic rearrangements.\u201d<\/p>\n Of course, this experiment wasn\u2019t designed just to prove Amontons wrong (after all, his laws do work remarkably well under normal circumstances), but whatever magnetic behaviors occur at these macroscales likely can occur under microscopic ones as well, potentially unlocking a range of micro<\/a>– and even nanoelectromechanical devices, including magnetic bearings and atomically thin magnets.<\/p>\n