Fast magnetic pulses trigger bits' flips 

An electron beam pierced these cobalt films at centers (small irregularities). A brief, induced magnetic pulse triggered magnetization flips from left-oriented to right-oriented in some areas. Like doomsday prophets, experts in the quest to pack data ever more quickly and densely onto conventional computer hard disks are again proclaiming, "The end is near!" They warn that current magnetic-recording methods are approaching fundamental limits on how quickly magnetic domains can reverse and how closely they can squeeze together.

 New research by Swiss and American scientists, however, suggests that there is still a future for the technology. Experiments reported in the Aug. 6 Science raise the possibility of a 1,000-fold increase in the speed of writing magnetic data.

 Christian H. Back of the Swiss Federal Institute of Technology (ETH) in Zurich and his colleagues created rapidly changing magnetic fields by using electrons accelerated to nearly the speed of light at the Stanford (Calif.) Linear Accelerator Center. They demonstrated that magnetic pulses as short as 2 picoseconds (ps) trigger reversal of magnetization-the equivalent of writing a new bit-in thin cobalt films. Today's fastest write heads require roughly 2 nanoseconds to switch a bit between 0 and 1.

 Once the magnetization shift begins, notes team member Wolfgang Weber of ETH, it takes a much longer period-up to 500 ps-to fully reverse direction. However, "what counts in writing bits is only the time to trigger them," he says.

 Although conventional wisdom dictates that ultrafast bit writing should require very high magnetic field strengths, the team triggered reversals using fields no greater than those from today's write heads, the scientists report.

"Getting the time down by a factor of 1,000 is just incredible. I'm impressed," comments H. Neal Bertram of the Center for Magnetic Recording Research at the University of California, San Diego. He notes that magnetic-recording experts had thought that a write pulse must endure at least 100 ps to induce a magnetic domain to switch polarity.

"There's hope this result can give [magnetic-recording-device designers] guidance and optimism," he says. "The industry needs that right now."

 To achieve such rapid triggering, Back and his coworkers tapped a well-established phenomenon that enabled their brief magnetic-field pulse to induce lingering effects. Zapping a thin film with a field lying both in the plane of the film and perpendicular to the existing direction of magnetization was known to tilt the magnetization out of the plane.

 The new experiments demonstrate that once that tilt gets started, the pulse's job is done. Intrinsic magnetic effects take over, and the magnetization swivels into the opposite orientation. Because the applied pulse's role is limited, fast triggering becomes possible without especially strong external field pulses, Weber explains.

 At this stage, no one expects these findings to trigger commercial products any time soon. Dieter Weller of the IBM Almaden Research Center in San Jose, Calif., another researcher on the team, jokes that the write head used in the experiment-a 2-mile-long linear accelerator-"is a bit clumsy." Whether ordinary write heads can generate magnetic field pulses like those made by the electron beam remains to be seen, he cautions.