In contrast to other common types of waves (e.g., electromagnetic or sound), the interaction of spin waves in magnetic materials is intrinsically non-linear due to dipolar coupling effects. The Spin is the intrinsic angular momentum of electrons that produces a magnetic moment. Coupling these magnetic moments creates the magnetism that could ultimately be used in information processing.
A magnetic field pulse can locally excite these linked magnetic moments, which can cause a dynamic to propagate across the material like waves. These are known as magnons or spin waves.
A team of physicists from Martin Luther University Halle-Wittenberg (MLU) has produced a new type of spin wave using alternating solid magnetic fields. Moreover, they provide the first microscopic images of these spin waves.
Professor Georg Woltersdorf from the Institute of Physics at MLU said, “Normally, the non-linear excitation of magnons produces integers of the output frequency – 1,000 megahertz becomes 2,000 or 3,000, for example. So far, it was only theoretically predicted that non-linear processes can generate spin waves at higher half-integer multiples of the excitation frequency.”
The team has now demonstrated the circumstances required to produce these waves and control their phase. Phase is the way a wave is oscillating at a specific moment in time.
Woltersdorf said, “We are the first to confirm these excitations in experiments and have even been able to map them.”
“The waves can be generated in two stable phase states, which means this discovery could potentially be used in data processing applications, since computers, for example, also use a binary system.”
Journal Reference:
- Dreyer R. et al. Imaging and phase-locking of non-linear spin waves. Nature Communications (2022). DOI: 10.1038/s41467-022-32224-0