Spin Transport in Nonmagnetic Materials
Spintronic circuits—which manipulate an electron’s spin rather than its charge—could allow computers and other electronics to run faster, without overheating. In electrically insulating magnetic materials, such as yttrium iron garnet, spin travels via waves that propagate from one spin to the next. Spin can also travel through nonmagnetic insulators by coupling to lattice vibrations called acoustic phonons. But the extent to which phonons can mediate spin currents in a circuit remains undemonstrated. Now Andreas Rückriegel and Rembert Duine, both at Utrecht University in the Netherlands, present a model that predicts that spin currents can propagate over long distances in materials impervious to external magnetic fields.
The duo modeled a nonmagnetic insulator sandwiched between two identical magnetic ones. They applied an electrical current to an adjacent metallic wire, causing a spin current to build within each magnetic insulator. These currents caused an elastic displacement of the acoustic phonons in all three layers, with the resulting magnetoelastic interactions between spins and lattice vibrations leading to a spin flow across the nonmagnetic insulator. The predictions of Rückriegel and Duine indicate that this current—whose strength depends on the width of the magnetic layers—could traverse millimeter-scale distances.
In recent experiments, researchers used a microwave field to excite a spin current in a half-millimeter-thick layer of nonmagnetic gadolinium gallium garnet sandwiched between two yttrium iron garnet films. The model developed by Rückriegel and Duine builds on that finding but uses an electrically driven current that is more practical for powering spintronic devices.
This research is published in Physical Review Letters.
Rachel Berkowitz is a Corresponding Editor for Physics based in Seattle, Washington, and Vancouver, Canada.