POWERFUL PULL TO NEW MAGNETS-Supply Problems with vital RARE-EARTH METALS attract new magnet-making methods by Mitch Jacoby, C&EN Chicago on January 7, 2013
David J. Sellmyer, a physics professor at the University of Nebraska, Lincoln, agrees. “In this field, that would be like setting out to hit a grand slam home run.” He explains that Nd2Fe14B magnets’ outstanding strength has made them indispensable to modern computer disk drives, a variety of large and tiny audio speakers, and many types of motors and motor generators crucial to the performance of hybrid automobiles and electricity-generating windmills.
The high strength of Nd2Fe14B and other rare-earth-based magnetic materials such as samarium cobalt (SmCo5) leads to powerful yet relatively small and lightweight magnets. That strength, which is often expressed as a “magnetic energy product,” can be on the order of 56 megagauss-oersteds (MGOe). A common refrigerator magnet, based on iron, is less than 1 MGOe.
One new research thrust in the bottom-up category takes its cue from the inner workings of rare-earth magnets. In Nd2Fe14B, for example, the transition metal is the source of the high magnetization. The rare-earth component is responsible for the high value of a property known as magnetocrystalline anisotropy, which is related to a magnet’s resistance to becoming demagnetized. The underlying idea is to engineer composite materials that combine high magnetization and high anisotropy components.
“The trick is bringing these components together on a very short length scale—about 10 nm,” Sellmyer says. At that scale, the two components are intimately tied to each other magnetically, or what experts in this field describe as strongly exchange coupled. The concept has been around since the 1990s, Sellmyer points out, but it has been difficult to implement. Despite recent advances in synthesizing a large variety of nanoparticles, researchers have found it challenging to control the size, crystal structure, and phase purity of exchange-coupled nanoparticles. One source of that challenge is a high-temperature treatment, usually above 500 °C—it causes nanoparticles to coalesce and grow to large size.
To overcome the size and structure problems, Sellmyer, Balamurugan Balasubramanian, and coworkers, including the University of Delaware’s George C. Hadjipanayis, developed a heat-treatment-free cluster deposition technique for making nanoparticles. In one application of that method, the team fabricated new rare-earth transition-metal nanoparticles by sputtering an yttrium-cobalt target. That process, which resembles atomic-scale sandblasting, generates vapors of Y and Co atoms that cool and directly aggregate into uniform-sized crystalline YCo5 and Y2Co17 nanoparticles measuring less than 10 nm in diameter. The proof-of-concept study shows that the method can be used to fabricate well-ordered magnetic nanoparticles for further analysis (Nano Lett., DOI: 10.1021/nl200311w).
The team also applied the method to making rare-earth-free hafnium-cobalt nanomagnets and nanocomposites of HfCo7 encapsulated in an FeCo phase. Like the Y-Co particles, the HfCo7 nanoparticles are also well ordered and tend to be less than 10 nm in diameter. Sellmyer points out that this sputter-based cluster methodology for making nanocomposites can be readily adapted to produce other types of permanent-magnet alloys including next-generation high-performance magnets (Appl. Phys. Lett., DOI: 10.1063/1.4753950).
NSF award aids UNL engineer's efforts
to build better solar cell
Released on 12/21/2012, Today@UNL
University of Nebraska–Lincoln
Jinsong Huang earned an NSF CAREER award to advance his research into solar energy devices.
The sun provides all the energy humans could ever need. But capturing that power remains expensive and inefficient, which leaves fossil fuels as dominant energy sources.
"Solar is one of the most renewable and convenient energies," Huang said. "People really want to convert solar energy into electricity, but it's too expensive now compared to fossil or nuclear energy. So we want to make solar competitive with other types of energy."
Today's solar cells use a semiconductor, almost exclusively silicon, sandwiched between two metal electrodes that create an electric field. One electrode is transparent to allow light to pass. The photons in sunlight knock loose the semiconductor's negatively charged electrons, which migrate within the system's electric field to form a current. That current is harnessed as electricity. Although silicon-based solar cells are efficient, they are expensive to produce and limited in their applications, Huang said.
To overcome silicon's limitations, scientists are working to replace it with organic polymers, or plastics, which are cheaper and more flexible, but also less energy efficient.
Louise Pound-George Howard Distinguished Career Award
Posted on 4/20/2012, College of Arts and Sciences
Since it was established in 1990, the Louise Pound-George Howard Distinguished Career Award has recognized individuals who have made an exceptional contribution to the university during their careers. These contributions have been through teaching, research, public service, administration or through a combination of these factors. The honored individuals also reflect a long-standing commitment to the university. ...more
Dr. David Sellmyer, founding director of the Nebraska Center for Materials and Nanoscience and George Holmes University Professor of physics and astronomy — Sellmyer’s research interests have focused on condensed matter physics and nanoscience. He has (co-)authored and edited more than 530 research articles, chapters and reviews, and eight books. He is a fellow of the American Physical Society, an honorary member of the State Key Magnetism Laboratory, Chinese Academy of Sciences, and won Outstanding Research and Creative Activity awards from the University of Nebraska and Sigma Xi. At UNL he has organized and pushed many collaborative research and education initiatives including a new nanoscience research facility that was completed this spring. It is in large thanks to his nearly 40-year record of dedication, vision, and continuing service that UNL now enjoys national prominence as one of the country’s leaders in materials and nanoscience research.
Dr. Mathias Schubert, University of Nebraska-Lincoln associate professor of electrical engineering, has been elected a fellow of the American Physical Society. Election to the fellowship is limited to no more than one-half of 1 percent of the society's membership.
The APS has 14 divisions and nine topical groups covering all areas of physics research. There are six forums that reflect the interests of its 43,000 members in broader issues and eight sections organized by geographical region.
Schubert was cited by the APS council at its November meeting for the "development of generalized ellipsometry and the invention of the Optical Hall Effect, and their transformative potential for industrial characterization of materials properties." Those materials could be developed into such things as liquid crystal displays or semiconductor device structures. read further...
Hong to use CAREER award to research nanoscale materials
Released on 04/30/2012, Today@UNL
University of Nebraska–Lincoln
Dr. Xia Hong, assistant professor of physics and astronomy and a researcher in UNL’s Materials Research Science and Engineering Center, earned a five-year, $600,000 Faculty Early Career Development Program Award from the National Science Foundation to continue her research.
For decades, scientists have been squeezing more power out of today’s silicon-based electronics, which are approaching the material’s fundamental limits. To continue advancing, researchers are exploring existing materials for unique properties at the nano-level and fabricating new nanomaterials with multifunctional properties. Many materials exhibit unusual physical, chemical or biological properties at the nanoscale that are not found at the larger macro level.
With her award, Hong will combine two oxides to create a multiferric nanomaterial with both magnetic and ferroelectric properties. Ferroelectric materials have positive and negative polarization directions. Applying electricity can reverse the polarization. In a multiferric material, electricity also can control magnetism. ...more
SPINTRONICS
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DISCOVERY COULD SPARK Smaller, Faster Electronics UNL Office of Research Researchers Document Spintronics Breakthrough Christian Binek and Peter Dowben together with theorist Kirill Belashchenko and "research team achieved a qualitative leap forward in modern spintronics," said Binek ...excerpt from the Scarlet, July 15, 2010 |
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UNL's Schubert named fellow in physics organizationReleased on 01/11/2012 |
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Nanohybrids Promise ‘Best of Both Worlds’
Annual Reports 2010-2011 from the Office of Research & Economic Development
University of Nebraska–Lincoln
Scientists are always seeking better ways to find and quantify minute things, such as toxins in the air or cancer particles in blood. UNL researchers lead a collaboration to create more powerful detection devices by combining manmade nanoparticles with nature’s inherent recognition capabilities.
Creating these “nanohybrids” requires the diverse expertise of researchers in biology, chemistry and nanomaterials engineering. A Nebraska team
recently launched the UNL-based Center for Nanohybrid Functional Materials, which brings together 15 researchers from UNL, the University
of Nebraska Medical Center, the University of Nebraska at Kearney, Creighton University and Doane College.
With nanohybrids, “you get the best of both worlds,” said UNL chemist Dr. Patrick Dussault, a Charles Bessey Professor, who co-leads the center
with Dr. Mathias Schubert, associate professor of electrical engineering.
Nanohybrids combine nanostructures – which can be engineered to behave uniquely under certain conditions, such as when subjected to a beam of light or radio energy – with chemical or biochemical agents, such as RNA or antibodies that can bind a specific substance. This new nanomaterial can both find and reveal its target.
Materials often behave differently at nanoscales, Dussault said. Understanding the basic sensing principles of nanohybrids is a major goal of the new group. With this knowledge, researchers hope to develop tools with enhanced detection capabilities.
Potential applications include devices that more selectively or sensitively diagnose diseases or find environmental contaminants. The ability to better detect toxins in air or water also could benefit national security.
The center builds on UNL’s strength in nanomaterials. With about $7.5 million in funding from the National Science Foundation through Nebraska EPSCoR, the center is creating a new core facility and partnering with several departments to hire new faculty, enhancing UNL’s leadership in nanoscience.
The center also has begun developing partnerships with industries in Nebraska and beyond.
”I think potentially it can attract a lot of companies, big and small, to Nebraska,” said Fred Choobineh, Nebraska EPSCoR director. “It’s very creative and cutting-edge research.”
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Carbon nano-onion illustration
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Harnessing Laser Power Creates Precise NanostructuresAnnual Reports 2010-2011from the Office of Research & Economic Development Carbon, the ubiquitous element of life, has many special properties. Harnessing it at the atomic level to create nanostructures promises to transform many everyday products, from computer chips to sunglasses. Discovering fast, cost-effective ways to mass produce these nanostructures is key to their practical use. It’s Yongfeng Lu’s specialty. “Carbon nanostructures have very large potential in different applications,” said Lu, Lott University Professor of Electrical Engineering. His UNL team has developed several unique processes that use lasers to make precise carbon nanostructures. They are refining their techniques and exploring new applications for their nanostructures. Since 2003, they have earned more than $14 million in research grants. Their laser-based production techniques can precisely control the length, diameter and properties of carbon nanotubes. Using these highly electrically and thermally conductive nanotubes, Lu’s team developed methods to improve transistors and sensors that may one day speed up computers and other electrical devices, while minimizing energy consumption and heat generation. They also discovered how to control a carbon nanotube’s diameter from one end to the other, which alters its characteristics. Lu envisions variable- diameter nanotubes customized for specific uses. Now they’re studying how to join carbon nanotubes to make smaller, lighter wires that carry large amounts of current for use in electric cars and other products. Another breakthrough process creates carbon nano-onions, spherical nanostructures resembling onion layers that have unique electrical, optical and magnetic properties. Nano-onions can store large amounts of energy on their extensive surface area. Using nano-onions, Lu’s team has developed supercapacitors for high-density energy storage. Nano-onions also have optical limiting properties, absorbing light as it intensifies. Lu’s research could lead to improved eye protection, optical sensors, satellites and other optical-dependent materials. Lu’s team also developed a fast, single-step process using lasers to write graphene patterns on surfaces. A basic building block for other nanostructures, graphene resembles nanoscale chicken wire. Its electrical conductivity and transparency could be used in products such as LCD televisions and solar panels. “Carbon is everywhere, so the future of electronics, photonics and many high-tech industries will not be limited by supplies,” Lu said. |
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