In some crystals, the magnetic moments of atoms oscillate in sync, like a wave in a stadium. It carries spin without charge current, without heating the material. This flow resembles an invisible river — silent and cold. Two-dimensional altermagnets are special materials: spin waves in them run differently along different axes. But the crystal's shape can be changed. A light press is enough to shift the atomic layers and rearrange the magnetic paths — a ferroelastic transition. The spin flow instantly changes direction without external magnets: as if the course of water is turned with a simple hand movement. Testing on a CoTe2 monolayer using spectroscopy showed: when heated, a temperature gradient arises, and magnetic waves flow, carrying spin. The main surprise: the coefficient linking heat and spin current changes sign upon switching. In other words, with a light squeeze, the flow reverses — without a single magnet. This is a path to programmable chips based on spin waves: they barely heat up, save energy, and switch mechanically.
Magnons carry spin without charge movement, so they hardly heat the material: like a sound wave running along a chain without needing the links to move.
The idea of controlling flows without fields resembles the 'terraforming' technology in sci-fi, where landscapes are altered to create the desired currents.