Multiferroics are materials in which unique combinations of electric and magnetic properties can simultaneously coexist. They are potential cornerstones in future magnetic data storage and spintronic devices provided a simple and fast way can be found to turn their electric and magnetic properties on and off. In a promising new development, researchers with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) working with a prototypical multiferroic have successfully demonstrated just such a switch — electric fields. 

Ramamoorthy Ramesh and Chan-Ho Yang of Berkeley Lab’s Materials Sciences Division successfully demonstrated that electric fields can be used as ON/OFF switches in doped multiferroic films, a development that holds promise for future magnetic data storage and spintronic devices.

“Using electric fields, we have been able to create, erase and invert p-n junctions in a calcium-doped bismuth ferrite film,” said Ramamoorthy Ramesh of Berkeley Lab’s Materials Sciences Division (MSD), who led this research.

“Through the combination of electronic conduction with the electric and magnetic properties already present in the multiferroic bismuth ferrite, our demonstration opens the door to merging magnetoelectrics and magnetoelectronics at room temperature.”

Ramesh, who is also a professor in the Department of Materials Science and Engineering and the Department of Physics at UC Berkeley, has published a paper on this research that is now available in the on-line edition of the journal Nature Materials. The paper is titled: “Electric modulation of conduction in multiferroic Ca-doped BiFeO3 films.” Co-authoring the paper with Ramesh were Chan-Ho Yang, Jan Seidel,Sang-Yong Kim, Pim Rossen, Pu Yu, Marcin Gajek, Ying-Hao Chu, Lane Martin, Micky Holcomb, Qing He, Petro Maksymovych, Nina Balke, Sergei Kalinin, Arthur Baddorf, Sourav Basu and Matthew Scullin.

The next generation of computers promises to be smaller, faster and far more versatile than today’s devices thanks in part to the anticipated development of memory chips that store data through electron spin and its associated magnetic moment rather than electron charge. Because multiferroics simultaneously exhibit two or more ferro electric or magnetic properties in response to changes in their environment, they’re considered prime candidates to be the materials of choice for this technology.

This image recorded after an electric field was applied to a calcium-doped bismuth ferrite multiferroic film shows in the top image current being conducted within the red rectangle (On). In the bottom image, an opposite electric field was applied to the area within the green rectangle, switching it back to an insulating state (Off).

This image recorded after an electric field was applied to a calcium-doped bismuth ferrite multiferroic film shows in the top image current being conducted within the red rectangle (On). In the bottom image, an opposite electric field was applied to the area within the green rectangle, switching it back to an insulating state (Off).

Bismuth ferrite is a multiferroic comprised of bismuth, iron and oxygen (BiFeO3). It is both ferroelectric and antiferromagnetic (”ferro” refers to magnetism in iron but the term has grown to include materials and properties that have nothing to do with iron), and has commanded particular interest in the spintronics field, especially after a surprising discovery by Ramesh and his group earlier this year. They found that although bismuth ferrite is an insulating material, running through its crystals are ultrathin (two-dimensional) sheets called “domain walls” that conduct electricity at room temperature. This discovery suggested that with the right doping, the conducting states in bismuth ferrite could be stabilized, opening the possibility of creating p-n junctions, a crucial key to solid state electronics.

“Insulator to conductor transitions are typically controlled through the combination of chemical doping and magnetic fields but magnetic fields are too expensive and energy-consuming to be practical in commercial devices,” said Ramesh. “Electric fields are much more useful control parameters because you can easily apply a voltage across a sample and modulate it as needed to induce insulator-conductor transitions.”

In their new study, Ramesh and his group first doped the bismuth ferrite with calcium acceptor ions, which are known to increase the amount of electric current that materials like bismuth ferrite can carry. The addition of the calcium ions created positively-charged oxygen vacancies. When an electric field was applied to the calcium-doped bismuth ferrite films, the oxygen vacancies became mobile. The electric field “swept” the oxygen vacancies towards the film’s top surface, creating an n-type semiconductor in that portion of the film, while the immobile calcium ions  created a p-type semiconductor in the bottom portion. Reversing the direction of the electric field inverted the n-type and p-type semiconductor regions, and a moderate field erased them.

“It is the same principle as in a CMOS device where the application of a voltage serves as an on/off switch that controls electron transport properties and changes electrical resistance from high (insulator) to low (conductor),” said Ramesh.

This schematic diagram shows a calcium-doped bismuth ferrite multiferroic film existing in a highly insulating state until the application of an electric field mobilizes  oxygen vacancies to create n- and p-type conductors in the top and bottom portions of the film respectively.

This schematic diagram shows a calcium-doped bismuth ferrite multiferroic film existing in a highly insulating state until the application of an electric field mobilizes oxygen vacancies to create n- and p-type conductors in the top and bottom portions of the film respectively.

Whereas a typical CMOS device features an on/off switching ratio (the difference between resistance and non-resistance to electrical current) of about one million, Ramesh and his group achieved an on/off switching ratio of about a thousand in their calcium-doped bismuth ferrite films. While this ratio is sufficient for device operation and double the best ratio achieved with magnetic fields, Chan-Ho Yang, lead author on this Nature Materials paper and a post-doc in Ramesh’s group says it can be improved.

Normal 0 false false false MicrosoftInternetExplorer4 “To make the ON state more conductive, we have many ideas  to try such as different calcium-doping ratios, different strain states, different growth conditions, and eventually different compounds using the same idea,” Yang said.

A year ago, Ramesh and his group demonstrated that an electric field could be used to control ferromagnetism in a non-doped bismuth ferrite film. (See Nature Materials, “Electric-field control of local ferromagnetism using a magnetoelectric multiferroic”)

With this new demonstration that the combination of doping and an applied electric field can change the insulating-conducting state of a multiferroic, he and his colleagues have shown one way forward in adapting multiferroics to such phenomena as colossal magnetoresistance, high temperature superconductivity and SQUID-type magnetic field detectors as well as spintronics.

Said Yang, “Oxides such as bismuth ferrite are abundant and display many exotic properties including high-temperature superconductivity and colossal magnetoresistance, but they have not been used much in real applications because it has been so difficult to control defects, especially, oxygen vacancies. Our observations suggest a general technique to make oxygen vacancy defects controllable.”

Much of the work in this latest study by Ramesh and his group was carried out at Berkeley Lab’s Advanced Light Source (ALS), on the PEEM2 microscope. PEEM, which stands for PhotoEmission Electron Microscopy, is an ideal technique for studying ferro magnetic and antimagnetic domains, and PEEM2, powered by a bend magnet at ALS  beamline 7.3.1.1, is one of the world’s best instruments, able to resolve features only a few nanometers thick.

“Without the capabilities of PEEM2 our experiments would have been dead in the water,” said Ramesh. “Andreas Scholl (who manages PEEM2) and his ALS team were an enormous help.”

This research was primarily supported by the U.S. Department of Energy’s Office of Science through its Basic Energy Sciences program.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California.  It conducts unclassified scientific research and is managed by the University of California.

Additional Information:

For more information on the research of Ramamoorthy Ramesh, visit his Website at http://www.lbl.gov/msd/investigators/investigators_all/ramesh_investigator.html

Fourteen partners have signed a Memorandum of Understanding (MoU) to create a permanent research platform called STRATOS. The MoU was signed by 12 PRACE partners, the Partnership for Advanced Computing in Europe, and two associated partners.

STRATOS stands for “PRACE advisory group for Strategic Technologies”. STRATOS has the goal to become a unique collaboration of PRACE partners and industry either directly or through consortia which include PRACE members. The objective of STRATOS is to foster the development of HPC (High Performance Computing) technologies in Europe.

The MoU was signed on 16 December, 2008 in Barcelona, Spain. 12 PRACE partners and one associated partner, the European industrial-academic association PROSPECT signed the MoU. The association Ter@tec acceded to the STRATOS MoU on 12 March, 2009.

Industrial and other innovative European HPC development projects engaged in development or evaluation of HPC technology can become members of STRATOS for the runtime of the projects.

The final cooperation agreement of the STRATOS partnership will be established as soon as the PRACE research infrastructure has become a European legal entity. During an initial period, STRATOS shall be governed by the MoU.

The following PRACE partners signed the MoU: Forschungszentrum Jülich (FZJ), Germany; Universität Stuttgart (HLRS), Germany; Leibniz-Rechenzentrum der Bayerischen Akademie der Wissenschaften (BADW-LRZ), Germany; Grand Equipement National de Calcul Intensif (GENCI), France; Barcelona Supercomputing Center (BSC), Spain; Netherlands National Computing Facilities Foundation (NCF), the Netherlands; Swedish National Infrastructure for Computing (SNIC), Sweden; CINECA Consorzio Interuniversitario (CINECA), Italy; CSC – IT Center for Science Ltd. (CSC), Finland; Eidgenössiche Technische Hochschule Zürich (ETHZ), Switzerland; Greek Research and Technology Network S.A (GRNET), Greece and Poznan Supercomputing and Networking Center (PSNC), Poland.

A team of students from the University of Utah’s School of Computing won a competition to build and run a small supercomputer cluster —a high-performance network used to perform intensive calculations for complex data sets such as weather forecasts or nuclear fusion.

Four national teams, including the U. students and a team from Skyline High School in Salt Lake City, were given identical components and two days to assemble and deploy a supercomputing cluster for a specific task. The competition, called the "LittleFe Challenge," was part of SC12, the annual international supercomputing conference held this year in Salt Lake City.

Utah computer science students Leif Andersen, Bruce Bolick, Ian King, Tom Robertson, Kathryn Rodgers and Tyler Sorenson were members of the winning team.

The competition involved what is known as the traveling salesman problem.

Three sets of cities and coordinates were given to each team. The students were then asked to use their small supercomputer to find the shortest route for a traveling salesman to take that would include a visit to each city once and a return to the city of origin for each data set using their cluster. The teams were judged on best score, visualization of their results and their knowledge of high-performance computing.

Brian Haymore, Martin Cuma and Wim Cardoen from the U’s Center for High Performance Computing were mentors to the team. Their faculty advisor was Mary Hall, a computer science professor.

Web inventor Tim Berners-Lee today returned to the birthplace of his brainchild, 20 years after submitting his paper 'Information Management: A Proposal' to his manager Mike Sendall in March 1989. By writing the words 'Vague, but exciting' on the document's cover, and giving Berners-Lee the go-ahead to continue, Sendall signed into existence the information revolution of our time: the World Wide Web. In September the following year, Berners-Lee took delivery of a computer called a NeXT cube, and by December 1990 the Web was up and running, albeit between just a couple of computers at CERN*.

Today's event takes a look back at some of the early history, and pre-history, of the World Wide Web at CERN, includes a keynote speech from Tim Berners-Lee, and concludes with a series of talks from some of today's Web pioneers. The full event will be webcast at http://webcast.cern.ch, and relayed via http://tf1.lci.fr/infos/endirect/0,,4301948,00-les-20-ans-du-web-edition-speciale-.html. Highlights will be available to broadcasters via a Eurovision worldfeed scheduled for 19:00CET
(http://www.eurovision.net/net/content/worldfeeds.php).

"It's a pleasure to be back at CERN today," said Berners-Lee. "CERN has come a long way since 1989, and so has the Web, but its roots will always be here."

The World Wide Web is undoubtedly the most well known spin-off from CERN, but it's not the only one. Technologies developed at CERN have found applications in domains as varied as solar energy collection and medical imaging.

"When CERN scientists find a technological hurdle in the way of their ambitions, they have a tendency to solve it," said CERN Director General Rolf Heuer. "I'm pleased to say that the spirit of innovation that allowed Tim Berners-Lee to invent the Web at CERN, and allowed CERN to nurture it, is alive and well today."

President Barack Obama today announced his intent to nominate physicist Patrick Gallagher to be the 14th director of the U.S. Commerce Department’s National Institute of Standards and Technology (NIST). Gallagher, 46, is currently the NIST deputy director.
 
“NIST is a unique agency with a strong culture of world-class scientific achievement,” U.S. Commerce Secretary Gary Locke said. “Pat Gallagher has come up through the ranks and his continued leadership will be critical to an agency that is central to the nation’s ability to innovate and compete in global markets.” 
 
If confirmed by the Senate, Gallagher will direct an agency with an annual budget of approximately $800 million that employs approximately 2,900 scientists, engineers, technicians, support staff and administrative personnel at two primary locations: Gaithersburg, Md., and Boulder, Colo. Gallagher will succeed William Jeffrey, who left NIST in 2007.
 
Though perhaps most widely known as the civilian provider of the nation’s standard time service, NIST also conducts research in measurement science, standards, and related technologies spanning all physical sciences, engineering and information technology. 
 
The agency also is home to the Hollings Manufacturing Extension Partnership, a nationwide network of local centers offering technical and business assistance to smaller manufacturers; the Technology Innovation Program, which provides cost-shared awards to industry, universities and consortia for research on potentially revolutionary technologies that address critical national and societal needs; and the Baldrige National Quality Program, which promotes performance excellence among U.S. manufacturers, service companies, educational institutions, health care providers and nonprofit organizations.
 
Gallagher, who has a doctorate in physics from the University of Pittsburgh, came to the NIST Center for Neutron Research (NCNR) in 1993 to pursue research in neutron and X-ray instrumentation and studies of soft-condensed matter systems such as liquids, polymers and gels. 
 
In 2000, Gallagher was a NIST agency representative at the National Science and Technology Council (NSTC) and became active in U.S. policy for scientific user facilities. In 2006, he was awarded a Department of Commerce Gold Medal, the department’s highest award, in recognition of this work. In 2004, he became director of the NCNR, a national user facility for neutron research that is considered one of the most productive and heavily used facilities of its type in the nation. In September 2008, he was appointed deputy director of NIST.
 
Gallagher is active in a variety of professional organizations and is a member of the American Association for the Advancement of Science.
 
Founded in 1901, NIST is a nonregulatory agency of the Commerce Department that promotes U.S. innovation and industrial competitiveness by advancing measurement science, standards and technology in ways that enhance economic security and improve our quality of life.