There is a surprising quantum effect in the material used in a hard disk drive. By controlling electron spin, researchers were able to affect information storage properties in metal alloy.
Researchers from the U.S. Department of Energy’s (DOE) Argonne National Laboratory, Oakland University in Michigan and Fudan University in China, found the quantum effect in metal alloy, a material which you might find in your hard disk drive.
Explaining the quantum effect
The effect is related to “damping”, in which the electron spin direction controls how the material dissipates energy. Olle Heinonen, a materials scientist at Argonne, described the quantum effect: “When you drive your car down a flat highway with no wind, the dissipating energy from drag is the same regardless of the direction you travel. With the effect we discovered, it’s like your car experiences more drag if you’re traveling north-south than if you’re traveling east-west.”
The researchers explained that atoms in a crystal structure sit at regular intervals arranged symmetrically. In certain alloys’ crystal structure, there are slight differences in the separation between atoms. These can be removed through the baking process.
Squeezing an alloy material such as this at the atomic level changes the separation of the atoms even more. The result is different interactions between atomic spins in the crystalline environment. This is the reason that the damping effect on magnetisation is large in some directions, and small in others.
Small distortions in the atomic arrangement within the crystalline structure of cobalt-iron alloy have large implications on the damping effect.
Controlling electron spin
Axel Hoffmann, another author of the study and Argonne materials scientist, explained: “In technical terms, we discovered a sizable effect from magnetic damping in nanoscale layers of cobalt-iron alloy coated on one side of a magnesium oxide substrate. By controlling the electron spin, magnetic damping dictates the rate of energy dissipation, controlling aspects of the magnetisation.”