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Research Bits: May 17

Magnetic storage structures; liquid crystal computing; fiber battery.


Magnetic storage structures
Researchers from The Ohio State University and Universidad Nacional Autonoma de Mexico investigated a new material that could potentially increase the capacity of magnetic storage devices.

They identified manganese germanide, an unusual magnetic material in which the magnetism follows helices, similar to the structure of DNA. The structure gives rise to a number of new magnetic patterns that could be used to store data.

“These new magnetic patterns could be used for next-generation data storage,” said Jay Gupta, a professor of physics at Ohio State. “The density of storage in hard disks is approaching its limits, related to how small you can make the magnetic bits that allow for that storage. And that’s motivated us to look for new materials, where we might be able to make the magnetic bits much smaller.”

The team used a scanning tunneling microscope with special tips to take pictures of the magnetic patterns with atomic resolution. In certain parts of the sample, the magnetism at the surface was twisted into a pattern resembling the spikes of a hedgehog. However, in this case the “body” of the hedgehog is only 10 nanometers wide, smaller than today’s magnetic bits that are about 50 nanometers.

They also found that the hedgehog patterns could be shifted on the surface with electric currents and inverted with magnetic fields. The researchers said this could allow reading and writing of magnetic data with less energy than currently possible.

“There is enormous potential for these magnetic patterns to allow data storage to be more energy efficient,” Gupta said, though he notes that there is more research to do before the material could be put into use on a data storage site. “We have a huge amount of fundamental science still to do about understanding these magnetic patterns and improving how we control them. But this is a very exciting step.”

Liquid crystal computing
Engineers from the University of Chicago figured out how to create the basic elements for logic operations in liquid crystals. Liquid crystals are most commonly known for their use in displays, but could also be used as a soft computing element in robotics.

“We showed you can create the elementary building blocks of a circuit—gates, amplifiers, and conductors—which means you should be able to assemble them into arrangements capable of performing more complex operations,” said Juan de Pablo, professor in molecular engineering at UChicago and senior scientist at Argonne National Laboratory. “It’s a really exciting step for the field of active materials.”

The key is in the structure of the liquid crystals themselves, and particularly in defects.

“The molecules in a liquid crystal tend to be elongated, and when packed together they adopt a structure that has some order, like the straight rows of atoms in a diamond crystal—but instead of being stuck in place as in a solid, this structure can also shift around as a liquid does,” wrote Louise Lerner, news officer for physical science and molecular engineering at UChicago. “One consequence of this odd molecular order is that there are spots in all liquid crystals where the ordered regions bump up against each other and their orientations don’t quite match, creating what scientists call “topological defects.” These spots move around as the liquid crystal moves.”

However, controlling the behavior of these defects is challenging. “Normally, if you look through a microscope at an experiment with an active liquid crystal, you would see complete chaos—defects shifting around all over the place,” said de Pablo.

The team found that by shining a light on specific areas of the liquid crystal they could guide defects to move in specific directions, opening up the possibility that the liquid crystal could be made to perform operations.

“These have many of the characteristics of electrons in a circuit—we can move them long distances, amplify them, and shut or open their transport as in a transistor gate, which means we could use them for relatively sophisticated operations,” said Rui Zhang, then a postdoctoral scholar at UChicago and now an assistant professor at the Hong Kong University of Science and Technology.

The researchers said that one particularly interesting application is in soft robotics. Another could be the use of the topological defects to move small amounts of liquid around in tiny devices such as synthetic cells. Next, the researchers plan to perform experiments to confirm the theoretical findings.

Fiber battery
Researchers from Massachusetts Institute of Technology, Huazhong University of Science and Technology, Kyung Hee University, and U.S. Army Research Laboratory developed a flexible fiber lithium-ion battery that could be woven into clothing or used as a structural element of devices.

The proof-of-concept battery built by the team was 140 meters long and manufactured using novel battery gels and a standard fiber-drawing system that starts with a larger cylinder containing all the components and then heats it to just below its melting point. The material is drawn through a narrow opening to compress all the parts to a fraction of their original diameter, while maintaining all the original arrangement of parts. This embeds the lithium and other materials inside the fiber, with a protective outside coating making it stable and waterproof.

“There’s no obvious upper limit to the length. We could definitely do a kilometer-scale length,” said Tural Khudiyev, at the time a postdoc at MIT and now an assistant professor at National University of Singapore. A demonstration device using the new fiber battery incorporated a Li-Fi communications system, in which pulses of light are used to transmit data, and included a microphone, pre-amp, transistor, and diodes to establish an optical data link between two woven fabric devices.

“When we embed the active materials inside the fiber, that means sensitive battery components already have a good sealing,” Khudiyev said, “and all the active materials are very well-integrated, so they don’t change their position” during the drawing process.

The 140-meter fiber is only a few hundred microns in thickness and has an energy storage capacity of 123 milliamp-hours, which can charge smartwatches or phones, Khudiyev said.

“The beauty of our approach is that we can embed multiple devices in an individual fiber, unlike other approaches which need integration of multiple fiber devices,” said Jung Tae Lee, previously a postdoc at MIT and now a professor at Kyung Hee University. They demonstrated integration of LED and Li-ion battery in a single fiber and he believes more than three or four devices can be combined in the future. “When we integrate these fibers containing multi-devices, the aggregate will advance the realization of a compact fabric computer.”

The material can also be used in 3D printing or custom-shape systems to create solid objects, such as casings that could provide both the structure of a device and its power source, such as in a toy drone submarine wrapped with the battery fiber.

“This is the first 3D printing of a fiber battery device,” Khudiyev said. “If you want to make complex objects” through 3D printing that incorporate a battery device, he said, this is the first system that can achieve that. “After printing, you do not need to add anything else, because everything is already inside the fiber, all the metals, all the active materials. It’s just a one-step printing. That’s a first.”

The team has applied for a patent on the process and is working on further improvements in power capacity and variations on the materials used to improve efficiency. They expect commercialization could happen within a few years.

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