Vortex ups and downs

Two new studies explore vortex core switching in ferromagnetic nanodisks, which could have implications for information storage

Credit: © 2007 APS

In ferromagnetic nanodisks, the magnetization tends to swirl in the plane of the disk. The magnetization at the centre of this magnetic 'vortex' can point either up or down — a binary state that could be useful for information storage. However, forcing the vortex core to flip from up to down can require a fairly large magnetic field or long switching times. Now, two separate teams look at different approaches to solving these technological hurdles.

In a combination of experimental and theoretical work, Teruo Ono of Kyoto University and colleagues in Japan and France¹, show that an oscillating current in which the electron spins are polarized in a certain direction is enough to switch the direction of a vortex core in a permalloy nanodisk. The idea is that the magnetic moments associated with the spins in the current exert a torque on the vortex core, causing it to change direction.

Meanwhile, physicists at the Research Centre in Jülich and the Max Planck Institute in Stuttgart, both in Germany, have simulated what happens when a short magnetic field pulse is applied in the plane of the disk². They find that a short pulse of only 60 picoseconds and 800 Gauss in strength (the earth's magnetic field is 0.5 Gauss) is enough to switch the vortex direction.

Taken together, the studies show that short magnetic field pulses provide fast switching, but electrical vortex switching may be more technologically viable. Bit by bit, however, magnetic vortices are becoming more promising candidates for information storage.