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Researchers discover surprising quantum effects in hard disk material



  Researchers discover surprising quantum effect in hard drive material
Argonne researchers have found a way to control the direction of electron spin in a cobalt-iron alloy, which affects its magnetic properties. The result could affect more powerful and energy efficient information storage materials. Picture credits: Argonne National Laboratory

Scientists are finding surprising ways to influence the information storage properties in metal alloys.

Occasionally, scientific discoveries can be found on well-trodden paths. This proved the case of a cobalt-iron alloy material commonly found in hard disk drives.

As reported in a recent issue of Physical Review Letters by researchers from the US Department of Energy (DOE) Argonne National, Laboratory has a surprising quantum effect in collaboration with Oakland University in Michigan and Fudan University in China found this alloy.

The effect involves the ability to control the direction of electron spin, and it could enable scientists to develop more efficiently Energy-efficient materials for information storage. By changing the electronic device in a material, the researchers were able to change their magnetic state. This increased magnetization control allows more information to be stored and retrieved in a smaller space. Greater control could also lead to further applications, eg. B. more energy efficient electric motors, generators and magnetic bearings.

The effect discovered by the researchers has to do with "damping", in which the direction of the electron spin controls the dispersion of the material energy. "If you drive your car on a flat highway without wind, the energy flowing away from the resistor is the same regardless of the direction of travel," said the materials scientist Olle Heinonen of Argonne, an author of the study. "With the effect we've discovered, it's as if your car is pulling more from north to south than traveling from east to west."

"From a technical point of view, we have found a considerable magnetic damping effect" nanoscale cobalt-iron alloy layers on one side of a magnesium oxide substrate, "added Argonne materials scientist Axel Hoffmann, another author of the study." By controlling the electron spin, magnetic damping determines the rate of energy dissipation and controls aspects of magnetization. "

The team's discovery proved particularly surprising, as the cobalt-iron alloy was widely used in applications such as magnetic hard drives for many decades, and its properties have been thoroughly studied. It was well known that this material was not preferred for electron spin and therefore magnetization.

In the past, however, scientists have prepared the alloy for use by "baking" at high temperatures "became what the Arrangement of the electrons in terms of cobalt and iron atoms in a regular grid, whereby the directional effect is eliminated. The team observed the effect by studying unbaked cobalt-iron alloys in which cobalt and iron atoms can randomly occupy each other's sites.

The team was also able to explain the underlying physics. In a crystal structure, atoms usually sit in symmetrical disposition at perfectly regular intervals. In the crystal structure of certain alloys, there are slight differences in the separation between atoms that can be removed by the baking process. These differences remain in an "unbaked" material.

Compressing such material at the atomic level further modifies the separation of the atoms, leading to different interactions between atomic spins in the crystalline environment. This difference explains that the damping effect on magnetization is large in some directions and low in others.

The result is that very small distortions in the atomic arrangement within the crystalline structure of the cobalt-iron alloy have huge effects on the damping effect. The team performed calculations at the Argonne Leadership Computing Facility, a DOE Office of Science user facility that confirmed its experimental observations.

The researchers' work will be published on March 21

in the online edition of Physical Review Letters and is titled "Giant Anisotropy of Gilbert Attenuation in Epitaxial CoFe Films."


Harddrive thrust exists in iron and cobalt layers


Further information:
Yi Li et al., Giant Anisotropy by Gilbert Damping in Epitaxial CoFe Films, Physical Review Letters (2019). DOI: 10.1103 / PhysRevLett.122.117203

Provided by
Argonne National Laboratory




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The Spindoctors: Researchers Discover Surprising Quantum Effect in Hard Disk Media (2019, April 25)
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