An animation shows how magnetic switch occurs in ferromagnetic and antiferromagnetic materials. Credit: Scott Schrage.
Most scientists wouldn't want to be called a spin doctor. The lab coat fits when it comes to the group of people.
The University of Nebraska–Lincoln physicists are working on a new class of data storage and processing called spintronics that will complement the digital electronics that have ruled the realm of high tech for decades.
Obstacles of the size belies their difficulty. The physicists may be on their way to surmounting an especially tricky one: finding order amid disorder and data amid seeming disarray, thanks to a $20 million National Science Foundation grant. Modern-day devices could look like sloths in retrospect if they were given two prizes, density and speed.
The spinners have digits.
The charge of the electrons flowing through the circuits is measured by electronics. The magnetism-related property of an electron's spin is called Spintronics. Devices that are fluent in both dialects of the same language can store and process more data, at faster speeds, with less power than their electronics-only counterparts.
Most electronic and spintronic memory has relied on ferromagnets, the type with a permanent magnetic field that is best known for pinning photos to fridges. ferromagnets have a spin that points in the same direction and can be changed by applying an external magnetic field.
They're popular in tunnel junctions, where two ferromagnets are sandwiched around a barrier with electrons moving between them. If the spin of an electron matches the spin of a ferromagnet, the electron will have less resistance. The flow of electric current is reduced when the spins don't match. The difference between those two states can be seen as a 1 vs. 0.
The cousins of ferromagnets have even more promise. The alternating columns of atoms that make up antiferromagnets have no net magnetic field. No magnetic field means no chance of a tunnel junction interfering with the magnetic state of a neighbor, which would allow engineers to pack more data-storage elements into a device without worrying about them corrupting each other's data.
Antiferromagnets are the choice if the next-gen devices need to speed up. The spins of a ferromagnet can be changed very quickly. That seems fast until you realize that the range of Picoseconds is 1,000 times faster than a ferromagnet. Antiferromagnets can keep pace, and they can be used in devices that are much faster.
It can be a bit like trying to write with a dried-up pen or decipher the writings of a toddler, if you're trying to decode data in antiferromagnets.
Tsymbal said that the problem is how to write and read information.
Tsymbal said that the antiferromagnetic property that acts as a pro in one context becomes a con when it comes to actually recording data. Writing a 1 or 0 in a ferromagnet is a simple matter of flipping its spin orientation. That is not possible in an antiferromagnet.
It's not easy to distinguish between the spin states of an antiferromagnet because neither produces a net magnetization that would yield differences in the flow of electrons. Efforts to develop antiferromagnetic tunnel junctions with practical use have been hampered by those facts.
Tsymbal said that this is one of the problems. I think we have a good way to solve this problem.
Tell up from the beginning.
An antiferromagnetic tunnel junction should be similar to a ferromagnetic one. An antiferromagnetic version relies on modifying the Néel vector, the axis along which spins are pointing one way or the other, rather than changing the overall magnetization of a ferromagnet.
Only specific types of antiferromagnets are suited to detecting spin-related differences in the flow of electrons, which are caused by mismatch between the Néel and the Nel vectors. The antiferromagnets have a secret. Both spin-up and spin-down electrons will flow through the channels.
Tsymbal and colleagues identified ruthenium oxide as an antiferromagnet. The barrier through which electrons can tunnel is found in titanium dioxide. The atoms of the two oxides form the same structure, which allows the electrons to maintain their spin as they move between the materials.
The Husker team has shown that it's possible to distinguish between the channels and their responses to different Néel vectors. The team's calculations show that the channel-specific magnetoresistance effect is similar to those produced by ferromagnetic tunnel junctions, and that it is an especially promising means of writing spintronic data that can also be read.
The University of Wisconsin-Madison's Chang-Beom Eom and other experimentalists are collaborating with Tsymbal to fabricate and test the antiferromagnetic tunnel junction. He and other members of the Nebraska Center for Materials and Nanoscience are looking at other materials that share the same characteristics as ruthenium oxide.
Tsymbal said that there are some antiferromagnets that have this property. We are going to look at these materials in the future.
The findings were reported in the journal.
Nature Communications has more information on spin-neutral currents for spintronics. There is a DOI of 10.1038/s41467-021-269.
Nature Communications is a journal.
The new data-decoding approach could lead to faster, smaller digital tech.
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