The promise of magnet or spin-based computing technology "spintronics"

BUFFALO, N.Y. -- What causes a magnet to be a magnet, and how can we control a magnet's behavior? These are the questions that University at Buffalo researcher Igor Zutic, a theoretical physicist, has been exploring over many years.

He is one of many scientists who believe that magnets could revolutionize computing, forming the basis of high-capacity and low-energy memory, data storage and data transfer devices.

Today, in a commentary in Science, Zutic and fellow UB physicist John Cerne, who studies magnetism experimentally, discuss an exciting advancement: A study by Japanese scientists showing that it is possible to turn a material's magnetism on and off at room temperature.

A material's magnetism is determined by a property all electrons possess: something called "spin." Electrons can have an "up" or "down" spin, and a material is magnetic when most of its electrons possess the same spin. Individual spins are akin to tiny bar magnets, which have north and south poles.

In the Japanese study, which also appears in the current issue of Science, a team led by researchers at Tohoku University added cobalt to titanium dioxide, a nonmagnetic semiconductor, to create a new material that, like a chameleon, can transform from a paramagnet (a nonmagnetic material) to a ferromagnet (a magnetic material) at room temperature.

Theoretical physicist Igor Zutic has been exploring ways to use magnets to revolutionize computing. A new article in Science may show that it is possible.

To achieve change, the researchers applied an electric voltage to the material, exposing the material to extra electrons. As Zutic and Cerne explain in their commentary, these additional electrons -- called "carriers" -- are mobile and convey information between fixed cobalt ions that causes the spins of the cobalt electrons to align in one direction. In an interview, Zutic calls the ability to switch a magnet "on" or "off" revolutionary. He explains the promise of magnet- or spin-based computing technology -- called "spintronics" -- by contrasting it with conventional electronics. Modern, electronic gadgets record and read data as a blueprint of ones and zeros that are represented, in circuits, by the presence or absence of electrons. Processing information requires moving electrons, which consumes energy and produces heat. Spintronic gadgets, in contrast, store and process data by exploiting electrons' "up" and "down" spins, which can stand for the ones and zeros devices read. Future energy-saving improvements in data processing could include devices that process information by "flipping" spin instead of shuttling electrons around.

In their Science commentary, Zutic and Cerne write that chameleon magnets could "help us make more versatile transistors and bring us closer to the seamless integration of memory and logic by providing smart hardware that can be dynamically reprogrammed for optimal performance of a specific task."

"Large applied magnetic fields can enforce the spin alignment in semiconductor transistors," they write. "With chameleon magnets, such alignment would be tunable and would require no magnetic field and could revolutionize the role ferromagnets play in technology."

In an interview, Zutic says that applying an electric voltage to a semiconductor injected with cobalt or other magnetic impurities may be just one way of creating a chameleon magnet.

Applying heat or light to such a material could have a similar effect, freeing electrons that can then convey information about spin alignment between ions, he says.

The so-far elusive heat-based chameleon magnets were first proposed by Zutic in 2002. With his colleagues, Andre Petukhov of the South Dakota School of Mines and Technology, and Steven Erwin of the Naval Research Laboratory, he elucidated the behavior of such magnets in a 2007 paper.

The concept of nonmagnetic materials becoming magnetic as they heat up is counterintuitive, Zutic says. Scientists had long assumed that orderly, magnetic materials would lose their neat, spin alignments when heated -- just as orderly, crystalline ice melts into disorderly water as temperatures rise.

The carrier electrons, however, are the key. Because heating a material introduces additional carriers that can cause nearby electrons to adopt aligned spins, heating chameleon materials -- up to a certain temperature -- should actually cause them to become magnetic, Zutic explains. His research on magnetism is funded by the Department of Energy, Office of Naval Research, Air Force Office of Scientific Research and the National Science Foundation.

The University at Buffalo is a premier research-intensive public university, a flagship institution in the State University of New York system and its largest and most comprehensive campus. UB's more than 28,000 students pursue their academic interests through more than 300 undergraduate, graduate and professional degree programs. Founded in 1846, the University at Buffalo is a member of the Association of American Universities.

Contact: Charlotte Hsu chsu22@buffalo.edu 716-645-4655 University at Buffalo

Electrohydrodynamic (EHD)-based thermal control, the technology promises to make it easier and more efficient to remove heat from small spaces

The more advanced the electronics, the more power they use. The more power they use, the hotter they get. The hotter they get, the more likely they’ll overheat. It doesn’t take a rocket scientist to understand what typically happens next: The electronics fry.

In the world of electronics, thermal control is always one of the limiting factors -- particularly in space where there is no air to help cool down electronic components.

However, Jeffrey Didion, a thermal engineer at the NASA Goddard Space Flight Center in Greenbelt, Md., and Dr. Jamal Seyed-Yagoobi, a professor at the Illinois Institute of Technology in Chicago, Ill., have collaborated to develop a technology that may overcome current limitations. They have formed technical partnerships with the U.S. Air Force and National Renewable Energy Laboratory to address the thermal-control concerns.

Called electrohydrodynamic (EHD)-based thermal control, the technology promises to make it easier and more efficient to remove heat from small spaces -- a particular challenge for engineers building advanced space instruments and microprocessors that could fail if the heat they generate is not removed.

"Today, higher-power computer chips are available, but they generate too much heat," said Didion, who is leading the technology-development effort also involving Matthew Showalter, associate branch chief of Goddard’s Advanced Manufacturing Branch, and Mario Martins of Edge Space Systems, an engineering company specializing in thermal systems in Glenelg, Md. "If I can carry away more heat, engineers will be able to use higher-power components. In other words, they will be able to do more things."

Technologists Jeffrey Didion (center), Matt Showalter (left), and Mario Martins (right) have developed a prototype pump that more efficiently removes heat from spacecraft instruments and components. Credit: NASA. Close-up of pump being tested on a Terrier-Improved Orion sounding rocket mission from the Wallops Flight Facility in June. Credit: NASA.

The project, a joint activity between NASA Goddard and its partners, received support from the Goddard Internal Research and Development (IRAD) program, which funds the development of promising new technologies that could advance NASA’s scientific and exploration goals. It is being demonstrated in June on a Terrier-Improved Orion sounding rocket mission, which also is flying the Small Rocket/Spacecraft Technology (SMART) platform, a microsatellite also developed at Goddard. This new microsatellite measures about 16 inches in diameter and was specifically designed to give scientific users less expensive access to space. The main objective of the EHD demonstration is showing that a prototype pump can withstand the extreme launch loads as the rocket lifts off and hurtles toward space. Should it survive the vibration, the technology will have achieved a major milestone in its development, Didion said. It will mean that it is at or near operational status, making it a viable technology for use on spaceflight instruments. "Any electronic device that generates a lot of heat is going to benefit from this technology," said Ted Swanson, assistant chief for technology for Goddard’s Mechanical Systems Division. This could include everything from sensors flown in space to those used in automobiles and aircraft. No Moving Parts The technology promises significant advantages over more traditional cooling techniques. Unlike current technologies used today by instrument and component developers, EHD does not rely on mechanical pumps and other moving parts. Instead, it uses electric fields to pump coolant through tiny ducts inside a thermal cold plate. From there, the waste heat is dumped onto a radiator and dispersed far from heat-sensitive circuitry that must operate within certain temperature ranges. "Its architecture, therefore, is relatively straightforward," Didion said. Electrodes apply the voltage that pushes the coolant through the ducts. "The advantages are many," he added. "Without mechanical parts, the system is lighter and consumes less power, roughly half a watt.

But perhaps more importantly, the system can be scaled to different sizes, from larger cold plates to microscale electronic components and lab-on-a-chip devices."

In addition to flying the technology on the sounding rocket mission, the EHD development team will fly a prototype EHD cold plate as an experiment on the International Space Station in 2013. "This effort will demonstrate the long-term operation of an EHD thermal-control system," Didion said.

Lab-on-a-Chip Devices

In the meantime, the team is continuing its work to further advance EHD, Didion said. The team is working with Goddard detector engineer Timothy Miller to develop EHD pumps in microchannels that are etched onto silicon wafers. They plan to further experiment with other substrate and composite materials as well as special micro-fabrication techniques and coatings to create smaller, more robust EHD pumps.

These multifunctional devices could be used as stand-alone, off-the-shelf components ideal for quick-turnaround spacecraft -- a capability that particularly interests the Air Force -- or as units embedded within the walls of the electronic device.

The next step is placing the technology on circuit cards, with the ultimate goal of scaling it to the chip level where the ducts would be no larger than 100 microns (0.0039 inch), or about the width of a human hair. "The point is that you want to place the thermal-control unit closer to the source of heat," Didion said. "This would be a lot more efficient at eliminating waste heat."

For more information, visit: gsfctechnology.gsfc.nasa.gov/HotWayCool Lori Keesey
NASA's Goddard Space Flight Center, Greenbelt, Md.