A compass needle turns slowly, but inside some materials, tiny magnetic moments can flip over timescales that are hard to imagine. A team of physicists has calculated how to make them change direction in a quadrillionth of a second — faster than a lightbulb blinks.
As a test case, they used the material Mn3Sn, a metal where the magnetic moments of atoms aren't aligned in parallel but at angles, forming an intricate triangular pattern. When a short pulse of spin current is sent through such a material, huge internal magnetic fields arise. They act like a powerful lever, rotating the pattern almost instantly. Previously, such switching took nanoseconds — a hundred thousand times longer.
The scientists showed that the rotation can not only be triggered but also reversed, just inject a spin current with the opposite spin direction. It's like turning a tuning knob the other way. This property makes the material a candidate for future memory: bits of information could be written not in billionths but in quadrillionths of a second.
The magnetic pattern in Mn3Sn resembles a gear with six possible positions. An ultrafast pulse flicks it from one stable state to another. If we learn to control this process, we could create devices that process information at speeds close to the limit set by nature itself.
A femtosecond is so short that light travels a distance hundreds of times smaller than the thickness of a human hair in that time.
In Peter Watts's novel Blindsight, ultrafast magnetic switching could underpin instantaneous communication between minds.