Single-Layer 2D Magnets Are Here
Scientists from the University of Washington and MIT have demonstrated that a monolayer of a two-dimensional material can exhibit an intrinsic magnetism.
This might seem like the latest in a series of seemingly similar announcements on 2D-material magnetism.However, this latest work differs from the others we’ve covered in that it demonstrates ferrimagnetism in a single layer of a 2D material without the use of an accompanying substrate to provide the magnetism.
Magnetocapacitance Turned Upside Down Offers a New Tool in Spintronics
Two years ago, research out of Brown University offered up a new approach to increasing the electric storage capacity in magnetic tunneling junctions—which among other things form the backbone of read heads in giant magnetoresistance (GMR) hard disk drives.
Now the same Brown researchers in collaboration with Japanese scientists have found a way to invert the effect and lower the capacitance of these junctions. The results could lead to the development magnetic sensors for “spintronic” applications including computer hard drives and next-generation random access memory (RAM) chips.
Nanosheets: IBM’s Path to 5-Nanometer Transistors
Researchers at IBM believe the future of the transistor is in stacked nanosheets. After a decade of research, most recently in partnership with Samsung and Global Foundries, the company will describe 5-nanometer node test chips based on these transistors today at the Symposium on VLSI Technology and Circuits in Kyoto.
Ferrimagnetism in a Two-Layer Material Opens New Doors in Computing
Scientists in Thomas Jung’s research groups at the Paul Scherrer Institute (PSI) and at the University of Basel in Switzerland have fabricated the first two-dimensional ferrimagnetic material that consists of only two layers of material.
Two-dimensional magnetic structures have been hotly pursued in the research community because the magnetic properties of single molecules in these structures can be indivdually addressed and modified. This is especially important in spintronics, where the aim is to use the spins of electrons to encode information.
In a three-dimensional magnetic material, it is difficult to determine, or change, the spin of an electron when there are lots of other layers of material on top or below it. Developing a 2D material that exhibits ferrimagnetism promises a much more effective way to perform spintronics for things like data storage or to use electrons’ spins as quantum bits in quantum computing.
With that in mind, researchers at Lawrence Berkeley Laboratory demonstrated last month that multi-layered examples of the 2D material chromium germanium telluride did have an intrinsic ferrimagnetism. However, these multilayered crystals (whose layers are held together by van der Waal forces) do not provide the advantages that ferrimagnetism would give in a monolayer.
Jung and his colleagues did not, strictly speaking, make a monolayer ferrimagnet either—the existence of which is impossible according to Heisenberg’s model of magnetic systems. Instead, in research described in the journal Nature Communications, they fabricated a monolayer comprising molecules called porphyrins. These organic structures, used in biochemistry and sensing applications, are about one nanometer in size. Right in the middle of each porphyrin molecule sits a magnetic atom—like iron. The molecules assemble themselves on top of a gold monolayer, forming a checkerboard pattern in which the spin of the magnetic atoms at the center of the molecules alternate between up and down.
Jung explained in an interview with IEEE Spectrum that without the gold surface—which is not magnetic but highly conductive—the system wouldn't be ferrimagnetic.
The gold’s conduction electrons couple themselves to the magnetic atoms at the center of the molecules, a phenomenon called the Kondo effect. Since the gold is a conductor but not magnetic it serves just as a sea of electrons below the magnetic molecules. The electrons in the gold surface are attracted to the opposite spins of the magnetic molecules above. This attracting of opposite spins leads to the kind of coupling in which one neighboring molecule knows about the situation of the next. This is critical for a magnetic system.
“Without the gold the magnetic molecules wouldn't know what the neighbor is doing; it wouldn't be magnetic at all,” says Jung. “Once we put the gold into this system the electrons below either of the spins recognize what is there and they tell their neighbor spins so that the neighboring atom knows from the electrons how it should behave.”
Jung is quick to caution that this is still fundamental research and should not really be considered a technology—say, a new data storage system—quite yet. In order for something like a data storage device to be developed out of this material, some kind of sensor would need to be developed to read the surface of the magnetic molecules. For the research described in the paper, a scanning tunneling microscope was able to go to one or the other of these spin centers and detect the Kondo effect locally.
In continuing research, Jung and his colleagues are looking at similar molecular architectures. But the metal atom at the center of their molecule will be manganese or cobalt instead of iron.
Jung adds: “In material science, you like to play with the ‘Legos’ and see if by combining different pieces we get something stronger with even more exciting properties.”
Nanogenerator Gets More Flexible and Transparent
Just last week, a research team in South Korea devised a way to improve the electrical output of the triboelectric nanogenerators (TENGs) developed by researchers at the Georgia Institute of Technology.
Not to be outdone, a team of scientists at Georgia Tech, led by Zhong Lin (Z.L.) Wang, have improved the capabilities of their TENGs technology by making them far more flexible. In the process, the team has given the devices a new name: skin-like triboelectric nanogenerators, or STENGs. These stretchy generators should provide another flexible power source for the increasing number of flexible electronics.
In research described in the journal Science Advances, the Georgia Tech researchers combined a hybrid material made up of an elastomer and an ionic hydrogel that can harvest energy from movement and provide tactile sensing. The flexibility and tactile sensing suggests that the material could be used to make self-powered electronic skin or self-powered soft robots.
Nanogenerators Could Charge Your Smartphone
Researchers at the Georgia Institute of Technology have been exploring the applications and commercial potential for triboelectric nanogenerators (TENGs) since 2012. These so-called TENGs essentially harvest static electricity from friction.
Now a team of researchers at Ulsan National Institute of Science and Technology (UNIST) in South Korea have overcome one of the hurdles preventing the technology from gaining wider adoption: low power output. To do this, they have developed a new polymer that serves as a dielectric material.
World's Thinnest Hologram Promises 3D Images on Our Mobile Phones
Holograms have fascinated onlookers for over half a century. But the devices for producing these holographic images have been relatively bulky contraptions, forced into their large size in part by the wavelengths of light that are necessary to generate them.
Emerging technologies such as plasmonics and metamaterials have offered a way to manipulate light in such a way that these wavelengths can be shrunk down. This makes it possible to use light for devices such as integrated photonic circuits. And just this week, we’ve seen metasurfaces enable an elastic hologram that can switch images when stretched.
Now, a team of researchers at RMIT University in Melbourne Australia and the Beijing Institute of Technology has developed what is being described as the “world’s thinnest hologram.” It is only 60 nanometers thick; they produced it not by using either plasmonics or metamaterials, but with topological insulators. The resulting technology could enable future devices capable of producing holograms that can be seen by the naked eye, and are small enough to be integrated into our mobile devices.
Artificial Photosynthesis Moves on From Water Splitting to CO<sub>2</sub> Reduction
The road toward commercial artificial photosynthesis has been a bumpy one. Stories like the so-called artificial leaf generated a lot of hype in 2011, but the company initially behind the technology—Sun Catalytix—soon abandoned their commercial efforts in 2012 when it became clear the economics simply did not add up.
While other companies that launched around this time, Hypersolar for example, have continued to try to make their technology work commercially, the scientific community seemingly has had far better luck advancing the fundamental science of photoelectrochemical reduction.
This scientific effort largely has been organized in the United States under the Department of Energy’s Joint Center for Artificial Photosynthesis (JCAP). IEEE Spectrum had the opportunity to sit down with scientists at the northern branch of JCAP, located at Berkeley National Laboratory. (The southern arm is at the California Institute of Technology in Pasadena.) Our discussion covered where the technology is at this point, what’s next, and how nanomaterials are helping to shape its development.
Elastic Hologram Can Switch Images When Stretched
New elastic holograms can switch the images they display as they get stretched, finds a new study by scientists at the University of Pennsylvania. These holograms could have applications in virtual reality, flat-panel displays, and optical communications, researchers say.
Conventional holograms are photographs that, when illuminated, essentially turn into 2D windows looking at 3D scenes. The pixels of each hologram scatter light waves falling onto them, making the light waves interact with each other to generate an image with the illusion of depth.
Penn scientists in Philadelphia had previously created holograms made of gold rods only nanometers or billionths of a meter large embedded within elastic films of silicone rubber. These new holograms are a kind of metasurface, which manipulate light using structures smaller than wavelengths of light.