The ability to control these properties has
The discovery focuses on a quantum-mechanical property known as spin, which endows electrons with a tiny magnetic field. Electron spin can point in either of two directions, "up" or "down," as does the accompanying magnetic field. Over the years, scientists have become adept at flipping the direction of spin, and therefore, the direction of the magnetic field. But the new finding has a novel twist.
In some materials, such as cobalt, the spins of neighboring electrons interact, causing them to all point in the same direction. If some of the spins are forced away from that direction, they pull some of the nearby spins with them. This causes the spins to undergo a gradual twist—clockwise or counterclockwise. In some materials, the spins prefer to twist in only one direction.
A team led by NIST researcher Samuel Stavis and Andrew Balk, now at the Los Alamos National Laboratory, found a way to control the direction of this twist in a film of cobalt just three atomic layers thick. Moreover, they could set this direction to be different at different locations on the same film of cobalt, and do so independently from other magnetic properties of the metal.
The team achieved this new capability by controlling an effect known as the Dzyaloshinskii-Moriya interaction (DMI), which imposes a preferred twist direction on spins. The DMI typically occurs at the boundary between a thin film of a magnetic metal and a nonmagnetic metal layer. The electron spins in the magnetic film interact with atoms in the nonmagnetic film, creating a preferential twist.
