Keeping the right material at the right angle, Cornell researchers have discovered a strategy for converting magnetism in the thin layers of a magnet — a technique that could eventually lead to the development of magnets. Magnetic memory devices are more energy efficient.
The group’s article, “Tilt-rotating currents generated by the jet magnet Collinear Ruthenium Dioxide,” was published in the journal Nature Electronics. The paper’s co-authors are postdoctoral researcher Arnab Bose and doctoral students Nathaniel Schreiber and Rakshit Jain.
For decades, physicists have tried to change the direction of rotation of electron spins in magnetic materials by manipulating them with magnetic fields. But the researchers included Dan RalphFR Newman Professor of Physics in the College of Arts and Sciences and lead author of the paper, instead sought to use spin currents carried by electrons, which exist when electrons rotate in the same direction. .
When these spin currents interact with a thin magnetic layer, they transfer their angular momentum and generate enough torque to shift the magnetization 180 degrees. (This transition of magnetic direction is how people write information to magnetic memory devices.)
Ralph’s group has focused on finding a way to control the direction of rotation of eddy currents by making them with antiferromagnetic materials. In an antimagnet, all electrons rotate in the opposite direction, so there is no net magnetization.
“Essentially, the antiferromagnetic ordering can reduce the symmetry of the samples enough to allow unusual orientations of the rotational currents,” says Ralph. “The mechanism of the antimagnets also seems to provide a way to actually get quite strong eddy currents.”
The team experimented with the antimagnet ruthenium dioxide and measured how its rotating current tilted the magnetization in a thin layer of a nickel-iron magnetic alloy called Permalloy, which is a soft magnet. To map out the different components of the torque, they measured its effect at various angles of the magnetic field.
“At first we didn’t know what we were seeing. It was completely different from what we had seen before, and it took us a lot of time to figure out what it was,” Jain said. “Also, these materials are difficult to integrate into memory devices, and our hope is to find other materials that will exhibit similar behavior and can be easily integrated. ”
The researchers eventually identified a mechanism known as “momentum-dependent spin splitting,” which is unique to ruthenium oxide and other antimagnets in its class.
“For a long time it was thought that in antimagnets spinning up and down electrons always behave the same. Ralph said. “The up and down electronic states have fundamentally different dependencies. Once you start applying an electric field, that immediately gives you a way to create a strong spin current because the spin up and spin down electrons react differently. So you can speed up one of them more than the other and get strong rotational currents that way. “
This mechanism has been hypothesized but has never been documented before. When the crystal structure in the antimagnet is properly oriented in the devices, the mechanism that allows the current to rotate at an angle can enable more efficient magnetic transitions than other rotational orbital interactions. .
Now, Ralph’s team is hoping to find a way to create antimagnets in which they can manipulate the domain structure – i.e. regions where the magnetic moments of electrons align in the same direction – and study each one of them. individual domains, which is a challenge because of normal mixed domains.
Ultimately, the researchers’ approach could lead to advances in magnetic random access memory matching technology.
“The hope is to create very efficient, very dense and non-volatile magnetic memory devices that can be improved upon existing silicon memory devices,” says Ralph. “That will enable a real change in the way memory is implemented in computers because you will have something that is essentially infinitely durable, very dense, very fast, and the information persists. even when the power is off. No memory does that these days. “
The source: Cornell University
