X-Ray Microscopy of Spin Wave Focusing using a Fresnel Zone Plate

TL;DR

This paper demonstrates the first experimental realization of spin wave focusing using a Fresnel zone plate lens, enabling direct imaging of nanometer-sized focal spots and controllable steering of the focus via bias field adjustments.

Contribution

It introduces a novel spin wave focusing method with a Fresnel zone plate lens and demonstrates direct imaging and controllable steering of the focused spin waves.

Findings

First demonstration of spin wave focusing with a Fresnel zone plate.

Direct imaging of nanometer-sized spin wave focal spots.

Steering of the focal spot by small bias field variations.

Abstract

Magnonics, i.e. the artificial manipulation of spin waves, is a flourishing field of research with many potential uses in data processing within reach. Apart from the technological applications the possibility to directly influence and observe these types of waves is of great interest for fundamental research. Guidance and steering of spin waves has been previously shown and lateral spin wave confinement has been achieved. However, true spin wave focusing with both lateral confinement and increase in amplitude has not been shown before. Here, we show for the first time spin wave focusing by realizing a Fresnel zone plate type lens. Using x-ray microscopy we are able to directly image the propagation of spin waves into the nanometer sized focal spot. Furthermore, we observe that the focal spot can be freely moved in a large area by small variations of the bias field. Thus, this type of lens provides a steerable intense nanometer sized spin wave source. Potentially, this could be used to selectively illuminate magnonic devices like nano oscillators with a steerable spin wave beam.