Goran Karapetrov (MSD) prepares a scanning tunneling microscope. The device can determine the surface structure of a sample at the atomic scale, leading to new discoveries about the interaction of magnetic fields and high-temperature superconductors. Photo by George Joch.

Dec. 5, 2005 -- Some of this week's stories:

Vortex 'chains' studied in superconductors

By Dave Jacqué

They look like tiny swirling dust devils on the surface of the superconductor: "vortices" that appear where magnetic fields interact with the material. Unlike harmless dust devils, however, vortices can sap a superconductor's ability to transmit current without resistance.

Knowing how vortices move and arrange themselves under various temperatures and magnetic fields, as well as how they are influenced by the physical properties of the material, is critical in maintaining supercurrent flow.

As part of the laboratory's intense focus on superconductors, a team of Argonne scientists has obtained, for the first time, detailed images of the interaction of magnetic vortices with artificial, nanoscale engineered defects in a superconductor. Understanding this interaction could help scientists reduce the vortices' current-sapping effects — or lead to fundamentally new superconductor designs for transmitting DC and AC electric power, and quantum logic devices based on vortex manipulation.

High-temperature superconductors, discovered in 1986, have attracted intense interest due to their ability to conduct electricity without resistance when cooled with liquid nitrogen. Previously, superconductivity was only known in metals cooled with liquid helium, which is much more difficult and expensive to produce and handle. High-temperature superconductors are now used in many applications, including RF filters for mobile telephone networks, magnetic resonance imaging (MRI) machines and particle accelerators.

A critical factor limiting applications for these superconductors is their response to magnetic fields, such as in electric motors. Magnetic fields reduce the amount of current a superconducting material can carry. The fields create swirling tubes of electrical current — vortices — in the superconducting material. Superconductivity is completely suppressed within these structures. (The individual structure of vortices and their arrangement were predicted by Alexei Abrikosov of Argonne's Materials Science Division, who won the 2003 Nobel Prize in Physics for his work on superconductors.) And as current flows through the superconductor, the vortices are pushed at right angles to the current flow by the Lorentz force. Vortex movement inside the material dissipates energy and produces resistance.

Scientists have discovered that vortices can be locked into position by "pinning" them to defects — tiny grains of non-superconducting substances embedded in the superconductor.

"Today, vortex pinning is the main thrust of superconductor research," said Goran Karapetrov (MSD), a lead researcher of the Argonne team that includes Maria Iavarone, Jan Fedor, Dan Rosenmann and Wai-Kwong Kwok (all MSD). "We are concentrating on the microscopic physics behind defects that hold the vortices in place and increase the current-carrying capability of the materials."

To learn more about vortices and their effects, the Argonne team uses low-temperature scanning tunneling microscopy, or STM. This sophisticated technique is used in fundamental research to obtain atomic-scale images of surfaces as well as essential information on the electronic states at and just beneath the surface. The atomic-scale images of the surface and its electronic structure allow the Argonne team to pin-point the positions of both the vortices that control the superconductivity and the defects that pin the vortices. Applying this powerful imaging technique to engineered defect structures is a major advance.

STM requires an extremely sharp conducting probe held close to the sample — at a distance of only a few atom-diameters. Electrons can jump the gap or "tunnel" between the sample material and the stylus, producing an electrical signal. The stylus slowly scans across the surface, raising and lowering to keep the gap between the surface and the tip constant. Recording the vertical movement of the stylus reveals the structure of the surface atom by atom.

"If the scanning tip touches the surface, the experiment is over," Karapetrov said. "These experiments are very precise. To visualize the surface, the tip comes within three to four Angstroms of the material. It has to be precisely that distance — within one hundredth of an Angstrom — in order to observe these effects."

Beyond developing sophisticated STM techniques, the team devised a method of preparing a sample with an atomically flat surface containing a periodic array of defects to pin the vortices.

"The size of each defect allows it to hold up to six vortices," Karapetrov said. "As the magnetic field increases beyond the saturation number of the defect, vortices appear outside the defect."

The vortices induced by a weak magnetic field attached themselves to the defects, as expected. As the scientists increased the magnetic field, STM images revealed additional vortices; those that couldn't find a home in a defect appeared alongside in orderly lines — a "chain." As the magnetic field was increased further, the vortex chains became denser, up to a specific, critical intensity; at this critical field the vortex chain split into two parallel chains. The transition was accompanied by a peak in the superconductor's critical current density — the measure of how well the superconductor carries large electric currents. The scientists were able to create additional parallel chains by further increasing the magnetic field.

"It's basically a phase transition," Karapetrov said. "This behavior was predicted theoretically more than 10 years ago, but it hadn't been possible to see it until this scanning technique was perfected."

The experiments marked the first time this phase transition from single to multiple chains had been directly observed. It was also the first time vortices have been studied in engineered samples with STM. Previously, creating superconductors with varying defect properties was done using randomly distributed defects created with heavy-particle accelerators like Argonne's ATLAS.

"The STM experiments using samples irradiated at ATLAS helped us a lot. But the ability to create engineered samples means we are free to make whatever geometry of defects fits best for the application," Karapetrov said. "We can design the material for vortex-pinning abilities and the best critical current by changing the fabrication parameters. Since the defects are created by lithography, we have full control over the geometry and internal structure." The lithographic process also allows researchers to vary the material in the defects, opening up a new avenue for research.

The research resulted in two published papers in Applied Physics Letters and Physics Review Letters : the first discussing the sample preparation, the second focusing on the research results. (APL 87, 162515 (2005), Phys. Rev. Lett. 95 (2005) 167002).

The research was funded by the U.S. Department of Energy's Office of Basic Energy Sciences _ Materials Science under contract No.W-31-109-ENG-38. The research is a result of an on-going collaboration with the Center for Microanalysis of Materials at the University of Illinois-Urbana and the Center for Nanoscale Materials at Argonne.

APS reveals key to better permanent magnets

By Catherine Foster

Permanent magnets are important in a broad variety of commercial technologies, from car starters to alternators for wind-power generation to computer hard drives. Researchers at Argonne have found new clues to making those magnets longer-lasting and more powerful.

Using the Western Hemisphere's most brilliant X-rays at the Advanced Photon Source, the researchers were able to see new details of rare-earth ions, a critical component of permanent magnets. The examination of the ions, probing their magnetism with unprecedented resolution, revealed that the presence of rare-earth ions in more than one atomic environment reduces the magnetic stability of the best-performing permanent magnets to date. This knowledge will enable manufacturers to manipulate the rare-earth ion atomic structure to optimize future magnets.

The research is published in Physical Review Letters .

Rare-earth ions come from metallic elements that share similar chemical properties; they are not especially rare, but they are used sparingly because they are expensive to prepare. Rare-earth ions play an important role in determining magnetic stability against demagnetizing fields, and therefore in magnet performance.

"The research found that rare-earth ions in dissimilar crystalline environments compete with one another and undermine the magnetic performance of the highest performance magnets," said Argonne scientist Daniel Haskel (XFD), who led the research team. "These findings point to the need for specialized atomic engineering of the material — manipulating the rare-earth local atomic structure to fully utilize the rare-earth contribution in the next generations of magnets."

Other authors on the paper are Jonathan C. Lang, Zahirul Islam, Andrew Cady and George Srajer (all XFD), Michel van Veenendaal of Northern Illinois University, and Paul C. Canfield of Iowa State University.

Choral Group marks 25th season

The Argonne Choral Group will bring the sounds of the season to the laboratory Thursday, Dec. 8, with three performances marking the group's 25th season under the direction of Harry Bell (PFS-DR).

The choral group will perform in the Building 213 Cafeteria at noon, at the Argonne Credit Union at 1:15 p.m. and in the Building 201 Lobby at 2 p.m.

See info-line, Web site for operation changes

If winter weather becomes severe during the workday, the laboratory may release all employees early, except those deemed essential to operations.

Employees will be notified via the public address system and e-mail. Employees should use extreme caution when leaving the site, since conditions are likely to be hazardous. Employees deemed essential to operations should remain on site to work their regular shifts as assigned.

If severe weather occurs or continues overnight, the laboratory may delay opening. To find out about any changes to laboratory operations, call the Argonne Info-Line at (630) 252-4636 or check the Argonne Home Page at www.anl.gov. Radio and TV stations have proven to be unreliable in the past, and will not be notified.

Contact your supervisor if you have questions.

Foot pain topic of seminar

Podiatrist Paul Martin will talk about the causes and cures of painful feet as part of Diabetes Awareness month.

The talk will begin at 1 p.m. Wednesday, Dec. 14, in the Building 213 Cafeteria, Dining Rooms A and B.

For more information or to register, contact the Medical Department at ext. 2-2800.

2005 Performance Appraisals due to HR Dec. 19

This year's performance appraisal cycle is coming to a close. All performance appraisals are due electronically to Human Resources by Monday, Dec. 19.

At this point in the process, performance appraisals have been approved by your division and are ready to be released to employees. What are the next steps?

Next steps for employees

Employees will receive an e-mail letting them know that they may now view or print completed performance appraisals on the Web application.

Next, employees will have a conversation with their supervisors to discuss the performance appraisal.

After the meeting, employees will receive another e-mail letting them know they can sign their performance appraisals electronically.

Next steps for supervisors

After division approval, supervisors may release completed performance appraisals electronically to employees for viewing or printing.

After meeting with employees to discuss their performance appraisals, supervisors must electronically document the date of the meeting. At this time, they may also add comments and edit the employee's section 3 goals.

If the employee signs the performance appraisal with no comments, the performance appraisal is completed and will be forwarded to Human Resources. If the employee adds comments, both the supervisor and the second-level supervisor must review the comments and re-sign the performance appraisal electronically before the performance appraisal is completed and forwarded to HR.

Detailed instructions are on the Performance Appraisal Web page.

R&D 100, Green Chemistry entries are due

Argonne entries for the R&D 100 Awards and Green Chemistry Challenge Awards are being requested by the Office of Technology Transfer (OTT).

R&D 100 awards are presented annually by R&D magazine to recognize the "100 most technologically significant products" of the preceding year. The Presidential Green Chemistry Challenge Awards acknowledge innovative technology that promotes industrial ecology or reduces or prevents pollution in a significant way. Application or commercial use of the technology is also important in this award.

R&D 100 candidates must be technologies or products that are available for license to industry or could be ordered as products in 2005. The entry will be strengthened if there is tangible evidence of private-sector interest, such as a cooperative research and development agreement, joint venture, partnership with industry, licensing to industry or some other contractual arrangement with industry.

Final entries for Green Chemistry are due to OTT by Friday, Dec. 16. Final entries for R&D 100 are due to OTT by Friday, Feb. 10, 2006. For additional information, contact Cynthia Wesolowski (OTT) at ext. 2-7694 or weso@anl.gov.

Holiday run set for Dec. 8

The Argonne Running Club will hold its Holiday Fun Run and Walk Thursday, Dec. 8, starting from Building 200 at noon.

There will be a three-mile running course and a two-mile walking course. Employees of all skill levels are welcome to participate. Refreshments will be served after the event.

More information about the Argonne Running Club is online.

Argonne post-docs benefit from career workshop

A panel of experts representing the University of Chicago, Argonne and industry recently provided advice to Argonne postdoc appointees to support them in their job searches. The workshop, "Packaging Your Ph.D. to Find a Job," was held Nov. 19 in response to a request from the postdocs and on the recommendation of the Argonne postdoc committee.

Invited panelists shared experiences from their own job searches and insights as hiring managers. Panelists included:

Heather Sevener, assistant director of graduate services, Biological Sciences and Physical Sciences, University of Chicago

KaYee Lee, Department of Chemistry, University of Chicago

Jim Kaduk, Inorganic Catalyst Characterization Group, Innovene LLC

Eric Isaacs, director of Argonne's Center for Nanoscale Materials

Handouts and copies of the PowerPoint presentations are posted on the post-doc Web pages.

Argonne will also work with the University of Chicago Graduate Services to send job postings to the Argonne postdocs. Contact Jan Buckley (HR) at ext. 2-9371 or jbuckley@anl.govfor more information.

Service Awards

Service Awards for November include:

40 Years

George W. Crabtree (MSD), Roger K. Smith, Jr. (ET).

35 Years

Hazel A. Harris (OCF), Anthony J. Policastro (DIS).

30 Years

Mary D. Knox (DIS).

25 Years

Roberta T. Riel (CMT).

20 Years

Debbie J. Leasure (PFS), Barbara A. Meurer (XFD), Daniel F. Sarro (TSD).

15 Years

Travis D. Blair (PFS), Joseph R. Kamely (TSD), Scott D. Massow (PFS), Frederick A. Monette (EA), Susan M. Underwood (OCF).

10 Years

James A. Corsolini (TSD), Anthony Evans (PFS), Sara M. Hahn (XFD), Daniel P. O'Brien (CIS).

5 Years

Erica N. Carter-Bean (EQO), Sophia Kowalczyk (PFS), Mark H. Walker (PFS).

Retirees

Joseph Kamely (TSD-CS) retired Nov. 30 with 15 years of service.

Jo Ann Parnell (ES) retired Nov. 11 with 30 years of service.

Gerald Salotti (OTD) retired Nov. 4 with 12 years of service.

Argonne sweatshirts, T-shirts available

New Argonne T-shirts and sweatshirts are available for purchase at the Division of Educational Programs in Building 223, Room M114.

Sweatshirts cost $16-$18 and are available in black, navy blue, red, maroon, forest green, denim, khaki and violet. Available sizes are adult small to 2-XL.

T-shirts are $10-$12 and are available in black, navy blue, denim, dark brown, forest green, kiwi, orange and turquoise. Available sizes are adult small to 3-XL.

Contact Lisa Reed at lreed@dep.anl.gov for more information.

New security software available for home use

Argonne's Cyber Security Program Office has purchased Trend Micro PC-Cillin Internet Security for employees of the laboratory to install on their home computers.

Every year, when the contract renews, the office receives new license keys to use with the latest version of the software. Employees should update the software on their home computers to the most current release in order to receive the latest pattern files.

The serial number and download information are online.

Virtual Private Network (VPN) software is required to access Inside Argonne and the download Web page from home. Employees are also encouraged to read "Securing Home Computers" at https://credentials.anl.gov/.

CIS classes

Computing classes offered by the Computing and Information Systems Division are held in Building 201, Room 167C. Unless otherwise noted, classes cost $225 and are limited to eight participants. Complete class descriptions, schedules and enrollment forms are online. For more information about enrollment procedures, contact Diane Cavazos (CIS) at ext. 2-7153 or dkcavazos@anl.gov.

Classes offered in December will include:

"Advanced Word 2003" (CIS124) — Monday, Dec. 5, 8:30 a.m. - 4:30 p.m. Prerequisite: Introduction and Intermediate Word.

"Advanced Excel 2003" (CIS127) — Tuesday, Dec. 6, 8:30 a.m. - 4:30 p.m. Prerequisite: Intermediate Excel.

"Advanced Access 2003" (CIS130) — Wednesday, Dec. 7, 8:30 a.m. - 4:30 p.m. Prerequisite: Intermediate Access.

"Introduction to PowerPoint 2003" (CIS131) — Thursday, Dec. 8, 8:30 a.m. - 4:30 p.m.

"Advanced PowerPoint 2003" (CIS132) — Friday, Dec. 9, 8:30 a.m. - 4:30 p.m. Prerequisite: Introduction to PowerPoint.

"Beginning Unix" (CIS564) — Tuesday, Dec. 13, 9 a.m. - noon is the first session. Wednesday, Dec. 14, 9 a.m. - noon is the second session. There is no cost for this course.

"vi Editor in Unix" (CIS567) — Friday, Dec. 16, 9 a.m. - noon. There is no cost for this course. Prerequisite: A general knowledge of Unix, especially Unix file management commands.

Ar'Gang

NEW ARRIVALS

A girl, Phoebe, born Aug. 12 to Jill and Devin Hodge (PFS); a boy, Isaiah Jamar, born June 9 to Montez and Khadeeja Poe (PFS-CU).

Proud grandparents: a grandson, Jack David Dos Santos, born July 13 to Pat Moonier (PFS-PMO); a granddaughter, Hannah Marie, born April 25 to Marie Rene Blasier (LEG); a granddaughter, Ella, born June 2 to Joni Christensen (OCF-PRO).

ACHIEVEMENTS

Congratulations to Jennifer Bludgen (TSP) on her graduation from Northeastern Illinois University. Sherese Humphrey (PFS-PMO) on her graduation from University of Phoenix. Melanie Johnson (PFS-PMO) on her administrative assistant certificate from Moraine Valley Community College. Cheryl Walker (PFS-PMO) on her associate of arts in General Studies from University of Phoenix.

WEDDINGS/ENGAGEMENTS

Congratulations to Nicole Kemp (PFS-CU) and Tom Henry (PFS-CU) on their Sept. 17 wedding; Carla Fisera (PFS-PMO) and James Bulka (HEP) on their June wedding.

GET WELL

Get well to Mary Kowalczyk (PFS-CU), Paul Agos (PFS-CU), Harold Harper (PFS-CU), and Marsha Dial (PFS).

FAREWELL

Good luck to David Ercoli (PFS-CU) who has left the laboratory.

PROMOTIONS

Promotions reported to Ar'Gang this month include: Patricia Engwall (PFS-PMO), who was promoted to budget administrator.

CONDOLENCES

Our condolences to Fred Kempke (PFS-CU) on the death of his grandmother; Anthony Young (PFS-CU) on the death of his mother; Scott Bresnahan (PFS-CU) on the death of his grandmother; David Kuzma (PFS) on the death of his father; Bruce Ende (PFS-CU) on the death of his father; Angie Hamilton (PFS-CU) on the death of her mother-in-law.

CONTRIBUTORS

Thanks to this issue's contributors: Sharon Giblin (LEG), Georgianne Lamb (PFS), Susan McKinney (PFS-PMO), and Karen Neumann (PFS).

Borders offers 20% discount

Argonne employees can save up to 20 percent on most items at Borders bookstores Dec. 5-11 with a discount coupon available at www.aim.anl.gov/.

The discount is offered courtesy of Borders and the Argonne Research Library.

Weight Watchers open house set

Weight Watchers will hold an open house Wednesday, Dec. 7, at noon in Building 200, Conference Room J183.

Employees will be able to register and prepay for a 10-week program. The cost is $120.

For more information, contact the Medical Department at ext. 2-2800.

Library Web site has physician information

Resources to help Argonne employees choose a doctor can be found on the Argonne Library Web site.

The American Board of Medical Specialties Certified Doctor Home Page can be used to verify if a physician is board certified.

The State of Illinois Professional License Look-Up lists physicians and other health professionals licensed in the State of Illinois. Search results include the licensee's name, license number, license status, city and state, original date the license was issued, license expiration date and a disciplinary action indicator.

Links to both sites are available on the Argonne Library Web site.

Argonne Club seeks 4 new board members

The Argonne Club Board requires four new members for 2006. Two current board members are up for re-election.

Members serve three-year terms and help plan the Argonne Club's activities, like Breakfast with Santa, the Argonne employee picnic, parties and group outings. The board meets once a month to plan these activities.

To volunteer for the Argonne Club Board, forward your name, phone extension and a short biographical sketch to Eric Lindert (PHY) at lindert@phy.anl.gov or for more information, contact Todd Hayden (HEP) at ext. 2-6143 or tahayden@anl.gov.

Voting will take place on the Argonne Club home page during the first three weeks of December.