Imaging and phase-locking of non-linear spin waves

Non-linear processes are a key feature in the emerging field of spin-wave based information processing and allow to convert uniform spin-wave excitations into propagating modes at different frequencies. Recently, the existence of non-linear magnons at half-integer multiples of the driving frequency has been predicted for Ni80Fe20 at low bias fields. However, it is an open question under which conditions such non-linear spin waves emerge coherently and how they may be used in device structures. Usually non-linear processes are explored in the small modulation regime and result in the well known three and four magnon scattering processes. Here we demonstrate and image a class of spin waves oscillating at half-integer harmonics that have only recently been proposed for the strong modulation regime. The direct imaging of these parametrically generated magnons in Ni80Fe20 elements allows to visualize their wave vectors. In addition, we demonstrate the presence of two degenerate phase states that may be selected by external phase-locking. These results open new possibilities for applications such as spin-wave sources, amplifiers and phase-encoded information processing with magnons. Many proposed spin-wave based devices make use of non-linear behaviour of spin-waves. Here, Dreyer et al show the emergence of non-linear spin waves oscillating at half-integer harmonics in the strong modulation regime. By applying super-Nyquist sampling Kerr microscopy they directly image these non-linear spin waves and demonstrate their phase-locking to an external frequency source.

Automated summary

This article introduces the key features of non-linear processes in spin-wave based information processing and their application in device structures. By directly imaging non-linear magnons and demonstrating their phase-locking properties, it shows the existence of spin waves oscillating at half-integer harmonics in the strong modulation regime.