Illustration on magnetic reversal patterns
Illustration on magnetic reversal patterns

Order from chaos: how magnon-polarons organize themselves

Research news item

Almost twenty years ago, a fundamental speed limit for magnetization reversal was proclaimed, due to the emergence of chaos at very short timescales. Researchers from HFML-FELIX Laboratory have now found that such chaos can actually give rise to self-organized magnetic patterns. Their results have been published in Nature Communications.

Surprising discovery

While studying how lattice vibrations driven at resonance can affect magnetization in an iron garnet, the team of researchers – Maxime Gidding, Thom Janssen, Carl Davies and Andrei Kirilyuk - saw something peculiar. Within nanoseconds after the arrival of a strong pump pulse from a cavity-dumped free electron laser at FELIX, sharp ripples of switched magnetization could be seen propagating outwards from the center of the irradiated spot (see figure).

Despite the fact that the pump spot is nearly homogeneous, this pattern of switched magnetization has very small feature sizes, on the order of micrometers. Such a small pattern, stemming from a much larger excitation, should simply not exist. Further work revealed that it is formed by a strong interaction of spins with the crystal lattice, forming special particles, called magnon-polarons, that coherently interact and condense into the pattern of switched magnetization.

Illustration on magnetic reversal patterns

Foundation for future research

The observed dynamic self-organization of magnon-polarons offers a surprising and counterintuitive approach to generating small-wavelength features. Moreover, the fact that the elastic waves and spin waves are phase-synchronized with each other leads to an intriguing direction for future research. The phenomenon of wave synchronization covers a very broad spectrum of science, with particular relevance in brain research, where wave entrainment guides learning processes and memory.

The discovery that self-organization and pattern formation can be directly visualized in the form of magnon-polarons reveals that magnetic materials offer an excellent model system to study such processes.

Article

M. Gidding, T. Janssen, C. S. Davies and A. Kirilyuk “Dynamics self-organisation and pattern formation by magnon-polarons” Nat. Commun. 14, 2208 (2023). https://www.nature.com/articles/s41467-023-37919-6

Contact information

Organizational unit
High Field Magnet Laboratory, FELIX Laboratory
About person
Prof. A.I. Kiriliouk (Andrei) , Dr C.S. Davies (Carl)