Pulse harbors magnetic mystery

By Kimberly Patch, Technology Research News

Swiss researchers have made three-dimensional images of a piece of ferromagnetic cobalt reacting to a magnetic field pulse. The pictures, which show in detail a quick, microscopic reaction that happens every time something is recorded on a magnetic medium, uncovered something unexpected.

Each bit, or magnetic domain, in ferromagnetic material has two magnetic states, which represent the ones and zeros of computer information. Strong magnetic fields cause bits to flip, or change their states. Understanding exactly how this process works may lead to faster, more efficient recording devices.

The researcher's images showed that the reaction is a very fast process that happens differently than previously thought, said Christian Back, a research assistant at the Swiss Federal Institute of Technology.

The researchers applied a short magnetic field pulse, or excitation, to a disk-shaped sample that was in a state of magnetic equilibrium. They caught the sample reacting to the pulse using time resolved scanning Kerr microscopy.

What they saw at first looked like what they expected -- a wave function. "At first glance it looks as if the magnetic excitation moves like a wave ... [But] at the boundary the apparent wave is reflected with a reversed sign," said Back.

This sign reversal when the wave was reflected back from the edge of the disk was unexpected, Back said. In fact, it conflicts with classical wave mechanics, and so it shows that the apparent wave motion is actually not a wave at all, he said. "This is most surprising and against conventional wisdom about the magnetization dynamics and magnets with a boundary," he said.

The results show that there's a lot to understand about the effects needed to design future, ultrafast recording devices. "It is already clear from our experiments that [even a small pulse is] a very complex process... that will have to be controlled in future devices, Back said.

The next step in the research is to make similar images using stronger, shorter magnetic field pulses. "We will try to create a field pulses strong enough to actually reverse the direction of the magnetization," said Back. In addition, the researchers plan to use samples with different shapes in order to determine what combination of shape and magnetic field duration and strength is most efficient for flipping a bit.

Back's research colleagues were Y. Acremann, M. Buess, O. Portmann, A. Vaterlaus and D. Pescia of the Swiss Federal Institute of Technology, and H. Melchior of the Swiss National Science Foundation. The research was funded by the Swiss Federal Institute of Technology and the Swiss National Science Foundation. The researchers reported their findings in the October 20, 2000 issue of Science.

Funding:   Government
TRN Categories:  Semiconductors and Materials
Story Type:   News
Related Elements:   Technical paper, "Imaging Precessional Motion of the Magnetization Vector," Science, October 20, 2000.


October 25/November 1, 2000

Page One

Disk-on-a-chip takes shape

Shaky table top sorts parts

Forked nanotubes are tiny transistors

Society goes on data binge

Pulse harbors magnetic mystery


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