Observing magnon-polarons using a nanostructured magnetic structure illuminated by short laser pulses

A team of physicists from Germany, Russia, Ukraine and the United Kingdom have found a new way to observe magnon-polarons using a nanostructured magnetic structure illuminated by short laser pulses. In their article published in the journal Physical review B, the group describes the extent of previous research involving magnon polarons to develop a better method for observing magnon polarons.

Magnons are quantized spin waves that carry information, but because they are difficult to manipulate, there have been no practical applications. Polarons are quasiparticles that have been used by researchers to study the interactions between atoms and electrons in solid materials. Both magnons and polarons are the subject of research efforts aimed at gathering more information in smaller spaces (for computers, smartphones, etc.). Some of this research has involved the use of phonons (lattice deformations) to excite magnons. In such work, energy is transferred in one direction only. In more recent work, the researchers produced reciprocal interactions that lead to the formation of magnon-polarons, hybrid quasiparticles that are no longer either phonons or magnons.

Devices capable of working with magnon-polarons remained elusive until last year, when a team at Lawrence Berkeley National Laboratory used a nanomagnet to observe a magnon-polaron. It is believed that this is a necessary step to create a device that can use them. In this new effort, the researchers built on that effort by developing a more sophisticated apparatus that allowed them to visualize a magnon-polaron for a longer period of time and in more detail.

The new device was made by carving the first grooves in a thin film of Galfenol. The grooves on the surface of the film served as a means of influencing the spatial distribution of phonons and magnons. The team then used a pump probe to observe magnons and phonons as they interacted during the formation of magnon-polarons. A secondary pulse probe was then applied as a means of measuring reflectivity. The final step was the application of a magnetic field to regulate the frequency of the magnon’s mode. In addition to giving researchers the opportunity to observe the formation of magnon-polarons, the apparatus allowed them to tune the hybrids as they formed to create a stronger hybridization between them.

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