Flip out ! Noncommital material could make for hypersensitive magnetic field direction detector

While the mysterious, unseen forces magnets project are now (mostly) well-understood, they can still occasionally surprise us. For instance, thin films of cobalt have been observed to spontaneously switch their poles—something that typically doesn’t happen in the absence of an external magnetic field. Researchers from the CNST and the University of Maryland have measured this phenomenon on the largest scale yet. Most magnets are “permanent,” meaning a magnetic field of some strength must be applied to reverse their north and south poles. This permanence enables the billions of tiny magnets in computer hard drives to reliably store data. It also allows nanomagnetic sensor technology, for example, in the magnetometers which detect the earth’s magnetic field in smartphone compasses. Making these devices more energy efficient will require magnets which are increasingly sensitive to external influences, such as small magnetic fields. However, as these magnets become more sensitive they also become more unstable, flipping from north to south and back, even with no magnetic field. The researchers mapped out this instability in a film of cobalt, only a few atoms thick, and determined the conditions under which the instability arises. They hypothesize that the development of magnetic technology will benefit from their continuously flipping cobalt films, which can function as extremely sensitive magnetic test beds. Many proposed devices implement layers of ferromagnetic material which, to be useful, must be controllable by an external influence. According CNST/UMD Postdoctoral Researcher Andy Balk, however, most magnetic materials are too stable to be influenced at all by small interactions, and researchers have no way of knowing if their proposed devices are even close to working. “As an alternative,” Balk says, “we could make a proposed magnetic device from our unstable film. This way, even if the film were influenced only a very small amount we would see, for example, slightly more north flips than south flips, and we would know we are on the right track.” The measurements were done with video-rate Kerr Interestingly, these fluctuations exhibit scale microscopy, a form of polarized light microscopy invariance—meaning that their behavior is the that can image the fine-grained details of a same regardless of the length scale on which material’s magnetic state. The scientists found they are observed—a property they share the magnetic fluctuations in the thin cobalt film with otherwise unrelated phenomena such as interact with each other; a fluctuation from north earthquakes and crumpling paper. to south will always have a corresponding nearby fluctuation from south to north.