The crystal Ca2RuO4 resembles a stack of thin sheets. Inside each sheet, the electron spins are arranged in strict order, like rows of soldiers on a parade ground. The bonds between the sheets are weak, and their sign can be flipped by slightly pulling the crystal apart.
When the crystal is stretched, this weak interlayer coupling changes sign, and the entire magnetic pattern rearranges. At the same time, the internal vibrations (magnons, a kind of sound wave in the world of magnetism) change their frequency. The difference reaches 0.3 terahertz: it's as if the same string sounded a note higher just because it was slightly tightened.
Such sharp sensitivity to stretching near a magnetic phase transition is a ready-made tool for ultrafast switches. Instead of complex magnetic fields, a light mechanical press is enough to retune a device.
Fine-tuning the sound in a crystal by simple stretching is a step toward devices where information travels not by electrons but by waves of magnetic order.
A frequency of 0.3 terahertz is about 300 billion oscillations per second. A pendulum of a wall clock makes that many oscillations in a thousand years.