The edge of a magnet works like a guitar fret: a string pressed near the edge sounds different, with a richer set of overtones. Magnetic waves in a thin strip of nickel and iron behave in much the same way. Physicists measured how magnetization waves traveling along the strip generate waves at twice and three times the frequency. The source was found where the magnetic field changes sharply: at the strip's edges and at the boundaries between differently magnetized regions.

Magnetization waves are like ripples running across water, except what oscillates is not the water but the direction of magnetization. When such a wave enters a place where the field is nonuniform (for example, near the edge of a sample) it starts to be "squeezed," like a string at a fret. As a result, its oscillations are no longer purely sinusoidal and generate additional frequencies — harmonics. In the same way, a vibrating guitar string produces not only the fundamental tone but also higher overtones.

The scientists used a tiny diamond sensor to see these waves in detail. The sensor, smaller than a human hair, was brought close to the strip's surface and recorded the magnetic field with high resolution. It turned out that harmonics are born precisely at the edges, not in the middle. Moreover, the higher the harmonic number, the shorter its wavelength and the more "twisted" it becomes, as if the wave acquires a rotation.

This discovery helps us understand how to control magnetic waves in microdevices. Magnetic waves are already used to transmit information in some experimental chips, and the ability to generate higher harmonics adds new "notes" to this instrument. Instead of changing the frequency of the entire wave, one can extract additional signals from the edges — much like drawing overtones from a string without touching its fundamental tone.