This was first deemed impossible. Apps include: novel, energy-efficient electronic devices, particularly integrated circuits. A spin wave is caused by a perturbation of local magnetisation direction in a magnetic material. Such a perturbation is caused by an electron with an opposite spin, relative to the magnetisation. Spin waves transmit these perturbations in the material. This research demonstrates for the first time that it is possible to transmit electric signals in an insulating material.
So far, electrical circuits based on spin waves have not been realised, since it turned out to be impossible to introduce a perturbation in the system large enough to create spin waves. FOM workgroup team have succeeded to use spin waves in an electric circuit by carefully designing the device geometry. This allows them to make use of the spin waves that are already present in the material due to thermal fluctuations, which requires a much smaller disturbance of the system and hence enables the spin waves to be used in an electric circuit.
The spin wave circuit consists of a 200 nm thin layer of yttrium iron garnet (a mineral and magnetic insulator, YIG in short), with a conducting platinum strip on top of that on both sides. An electron can flow through the platinum, but not in the YIG since it is an insulator. However, if the electron collides on the interface between YIG and platinum, this influences the magnetisation at the YIG surface and the electron spin is transferred. This causes a local magnetisation direction, generating a spin wave in the YIG.
The spin waves that the researchers send into the YIG are detected by the platinum strip on the other side of the YIG. The detection process is exactly opposite to the spin wave injection: a spin wave collides at the interface between YIG and platinum, and transfers its spin to an electron in the platinum. This influences the motion of the electron, resulting in an electric current that the researchers can measure.
The researchers already studied the combination of platinum and YIG in previous research. It was found that when spin is transferred from platinum to YIG, this also implies the transfer of heat across the interface. This enables the heating or cooling of the platinum-YIG interface, depending on the relative orientation of the electron spins in the platinum and the magnetisation in the YIG. http://www.eurekalert.org/pub_releases/2015-09/uog-fro091015.php
From left to right: a spin up electron (red) scatters at the interface between YIG and platinum. In the collision, the electron spin reverses (green). This process generates a spin wave in the YIG, which propagates and gets absorbed at the second YIG-platinum interface. The spin is then transferred to an electron in the platinum, causing that electron to flip its spin direction (down to up). This spin flip will give rise to an electrical current, which is measured in the experiment. CREDIT Cornelissen et al.
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