Mechanism 'splits' electron spins in magnetic material
Holding the right material at the right angle, Cornell researchers have discovered a strategy to switch the magnetization in thin layers of a ferromagnet — a technique that could eventually lead to the development of more energy-efficient magnetic memory devices.
The team’s paper, “Tilted Spin Current Generated by the Collinear Antiferromagnet Ruthenium Dioxide,” published May 5 in Nature Electronics. The paper’s co-lead authors are postdoctoral researcher Arnab Bose and doctoral students Nathaniel Schreiber and Rakshit Jain.
For decades, physicists have tried to change the orientation of electron spins in magnetic materials by manipulating them with magnetic fields. But researchers including Dan Ralph, the F.R. Newman Professor of Physics in the College of Arts and Sciences and the paper’s senior author, have instead looked to using spin currents carried by electrons, which exist when electrons have spins generally oriented in one direction.
When these spin currents interact with a thin magnetic layer, they transfer their angular momentum and generate enough torque to switch the magnetization 180 degrees. (The process of switching this magnetic orientation is how one writes information in magnetic memory devices.)
Ralph’s group has focused on finding ways to control the direction of the spin in spin currents by generating them with antiferromagnetic materials. In antiferromagnets, every other electron spin points in the opposite direction, hence there is no net magnetization.
“Essentially, the antiferromagnetic order can lower the symmetries of the samples enough to allow unconventional orientations of spin current to exist,” Ralph said. “The mechanism of antiferromagnets seems to give a way of actually getting fairly strong spin currents, too.”
The team had been experimenting with the antiferromagnet ruthenium dioxide and measuring the ways its spin currents tilted the magnetization in a thin layer of a nickel-iron magnetic alloy called Permalloy, which is a soft ferromagnet. In order to map out the different components of the torque, they measured its effects at a variety of magnetic field angles. More