Synopsis: Putting a damper on the spin-torque effect

The effects of torques caused by spin-polarized currents are often unwanted in magnetic nanostructures, but they can be diminished with the right design.
Synopsis figure
Illustration: Alan Stonebraker

Spin-torque—the torque induced on a magnetic layer due to a spin-polarized electric current passing through it—may lead to ways to control the operation of nanoscale magnetic devices. However, it is also a source of noise and instability in the future designs of magnetic recording read-heads that are only several tens of nm in size (see [1]).

Writing in Physical Review Letters, Neil Smith, Stefan Maat, Mathew Carey, and Jeffrey Childress of Hitachi Global Storage Technologies in San Jose, California, have found a way to increase the critical current for the onset of spin-torque induced oscillations, which could reduce this problem.

Smith and colleagues study a variant of a spin-valve stack: essentially a ferromagnetic layer with a fixed magnetization, a nonmagnetic spacer, and a second ferromagnetic layer in which the magnetization is free to rotate. An electric current passing perpendicular to the stack is polarized by one magnetic layer and this polarized current generates a spin-torque on the other layer. Beyond a critical current in either current direction, the spin-torque can induce instability oscillations in the free layer.

The Hitachi group modifies the free layer by adding a second, thinner ferromagnetic layer, separated from the first by a ruthenium spacer that mediates a strong antiparallel coupling between them. With this “synthetic-ferrimagnet,” the magnitude of the critical current increases by several fold, but only for one direction of electric current. This asymmetry is attributed to a spin-torque-induced coresonance of the two natural modes of oscillation of the synthetic ferrimagnet, which efficiently transfers energy out of the destabilized mode into the stable one. – Jessica Thomas

[1] J. Sun, Physics 1, 33 (2008).


More Announcements »

Subject Areas


Previous Synopsis

Next Synopsis

Related Articles

Viewpoint: A Boost for Superconducting Logic

Viewpoint: A Boost for Superconducting Logic

A new choice of materials leads to more practically useful superconducting spin valves. Read More »

Synopsis: Controlling Magnetism by Electricity

Synopsis: Controlling Magnetism by Electricity

Small voltages can control the magnetic properties of thin films at room temperature. Read More »

Viewpoint: Spin Transport Goes Ballistic
Semiconductor Physics

Viewpoint: Spin Transport Goes Ballistic

The injection of spins into a high-mobility two-dimensional electron gas is unexpectedly efficient, suggesting that new theories may be needed to describe spin transport in such systems. Read More »

More Articles