Controlling magnets in an entirely new way

A reversible system can flip the magnetic orientation of particles with a small voltage.

Using just a small applied voltage, MIT scientists and elsewhere have developed a method to switch the orientation of magnets. They created a way to switch the magnetic polarity of a ferrimagnet 180 degrees.

The discovery could usher in a new era of ferrimagnetic logic and data storage devices.

Scientists developed this new system using a film of material called gadolinium cobalt. The two elements in gadolinium cobalt form interlocking lattices of atoms, and the gadolinium atoms preferentially have their magnetic axes aligned in one direction. In contrast, the cobalt atoms point the opposite way.

Using a voltage, scientists split water molecules along the film’s surface into oxygen and hydrogen. The oxygen can be vented away while the hydrogen atoms or nuclei penetrate deeply into the material. This changes the balance of the magnetic orientations.

The change can potentially switch the net magnetic field orientation by 180 degrees.

Postdoc Manteo Huang said, “We found that by loading hydrogen into this structure, we can reduce the gadolinium’s magnetic moment by a lot. The magnetic moment measures the strength of the field produced by the atom’s spin axis alignment.”

MIT professor of materials science and technology Geoffrey Beach said, “Because the change is accomplished just by a change of voltage, rather than an applied electrical current that would cause heating and thus waste energy through heat dissipation, this process is highly energy efficient.”

“The process of pumping hydrogen nuclei into the material turns out to be remarkably benign. You would think that if you take some material and pump some other atoms or ions into that material, you would expand it and crack it. But it turns out for these films, and because the proton is such a small entity, it can infiltrate the bulk of this material without causing the kind of structural fatigue that leads to failure.”

Huang said, “That stability has been proved through grueling tests. The material was subjected to 10,000 polarity reversals with no signs of degradation.”

Beach said, “The material has additional properties that may find useful applications. The magnetic alignment between the individual atoms in the material functions a bit like spring. If one atom starts to move out of alignment with the others, this spring-like force pulls it back. And when objects are connected by springs, they tend to generate waves that can travel along with the material.”

“For this magnetic material, these are called spin waves. You get oscillations of magnetization in the material, and they can have very high frequencies.”

“They can oscillate upward of the terahertz range, which makes them uniquely capable of generating or sensing very high-frequency electromagnetic radiation. Not a lot of materials can do that.”

Beach said, “Relatively simple applications of this phenomenon, in the form of sensors, could be possible within a few years, but more complex ones such as data and logic circuits will take longer, partly because the whole field of ferrimagnet-based technology is relatively new.”

“The basic methodology, apart from these specific kinds of magnetic applications, could have other uses as well. This is a way to control properties inside the bulk of the material by using an electric field.”

“That by itself is quite remarkable. Other work has been done on controlling surface properties using applied voltages, but the fact that this hydrogen-pumping approach allows such deep alteration allows “control of a broad range of properties.”

Journal Reference:
  1. Huang, M., Hasan, M.U., Klyukin, K. et al. Voltage control of ferrimagnetic order and voltage-assisted writing of ferrimagnetic spin textures. Nat. Nanotechnol. 16, 981–988 (2021). DOI: 10.1038/s41565-021-00940-1

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