Giant magnon spin wave conductance in ultrathin insulators surprises researchers
The current (I) through the injector electrode generates magnons in the thin YIG layer. These flow towards the detector electrode, where they produce an electrical voltage (V). Credit: University of Groningen / Xiangyang Wei

Conducting wires go up when thinner is made. It is generally right. When wires are so thin that they are effectively two-dimensional, there is an exception. The magnetism of magnons, spin waves that travel through magnetic insulators, are similar to a wave through a stadium according to physicists at the University of Groningen. The increase in conductivity was amazing. The observation was published in the journal Nature Materials.

The spin of electrons has a value of up or down. It is possible to send a current through a heavy metal and get a spin. The electrons cannot pass through the YIG when they encounter it. The spin excitation is passed on at the interface with YIG. The spin wave is similar to a wave in a stadium, with no electrons moving from their place, but it still passes on the spin. Bart van Wees is Professor of Applied Physics at the University of Groningen and specialist in fields such as spintronics.

The increase of electron mobility in 2D materials inspired his group to test magnon transport in ultrathin YIG films. The magnons can only move in two dimensions when the film is thin. The spin conductivity went up by three orders of magnitude when compared to YIG bulk material.

The effects are dramatic.

Van Wees said that scientists don't use terms like "giant" lightly. The material went op 1000 times after we made it thinner. This didn't happen at low temperatures because it's necessary for high electron mobility in 2D conductors. So far, this result has not been explained. The transition from 3D to 2D magnon transport is the subject of our paper. Dramatic effects can't be fully explained by that.

What could be done with this huge magnon? Van Wees said they don't understand it. Our claims are limited at this time. This could lead to some new undiscovered physics. This could produce new devices in the future. There is no electron transport involved in the magnon waves. It's a big problem in smaller electronic devices.

It's superconductivity.

It might be possible to create a coherent state similar to a Bose-Einstein condensate. This could even produce spin superconductivity. It's for the future. The conductance in YIG is documented. It's clear that the measurements are clear. There will be a good collaboration of theoretical physicists and experimentalists.

More information: X.-Y. Wei et al, Giant magnon spin conductivity in ultrathin yttrium iron garnet films, Nature Materials (2022). DOI: 10.1038/s41563-022-01369-0 Journal information: Nature Materials