“The spins are aligned in a way that if you walk through the hedgehog structure they twist in a spiral fashion in each direction,” explained Kai Litzius from Johannes Gutenberg University. “Because the twist is always in the same direction, the structure is called topologically protected.
“This term means that removing the skyrmion is a difficult process: it is like trying to remove the hair whorl on the back of your head. You will always have a small region of hairs pointing into a different direction - here it is outward.”
Since the skyrmions are stable, they are being considered for use in future magnetic storage devices. One of these approaches, magnetic shift register, or racetrack memory, promises low access times, high information density, and low energy consumption.
“You can imagine the ‘track’ as a small wire made of magnetic material, Litzius said. “The skyrmions would be the ‘cars’ moving along the track. Reading and writing of information on the device would be performed at fixed positions, either creating/removing a car (writing) or watching the cars pass by without interfering (reading).”
Since skyrmions can be shifted by electrical currents and feel a repulsive force from the edges of the magnetic track as well as from single defects in the wire, they can move undisturbed through the track.
“Just consider if a specific car had already passed the read unit, because it read another information first,” described Litzius. “What you do is reverse the current and shift all the skyrmions backwards until you reach the interesting slot in your chain again. This process must be able to happen millions of times to make a memory device reliable.”
“What we did in the experiment was to apply bipolar current pulses to the system. In this way, we were able to move the train of skyrmions back and forth billions of times,” Litzius concluded.