In the laboratories of Tokyo University of Science and Tohoku University, scientists discovered a simple yet reliable guide for predicting the magnetic properties of complex alloys. The size of the repeating structural cell of the crystal turned out to be a more accurate divider of different types of magnetism in materials related to quasicrystals than the usual electron concentration.
The researchers studied Tsai-type approximant crystals — structures with nested atomic clusters that replicate the features of true quasicrystals. In gold-containing compounds with aluminium or gallium and rare-earth elements (terbium, dysprosium, holmium), the magnetic behaviour depended on the lattice parameter — the distance between repeating atomic sites.
At a value greater than 14,72 angstrom, a "vortex" antiferromagnetic state arose: the magnetic moments of the atoms arranged themselves into an ordered but oppositely directed configuration. In the narrow interval of 14,62–14,72 angstrom, vortex ferromagnetism with a net magnetisation appeared. Below this threshold, the material transitioned into a spin-glass state — a chaotic freezing of moments without long-range order.
Previously, scientists focused mainly on the number of valence electrons per atom. This indicator performed unstably when the chemical composition changed. The new structural criterion yielded a unified phase diagram that now serves as a practical map for the search for and creation of materials with specified magnetic properties.
The discovery is important not only for fundamental physics. It opens the way to the purposeful design of quantum materials, where unusual magnetic states may become the basis of future devices — from sensors to elements of quantum computing. The slightest change in the dimensions of the atomic "room" radically alters the behaviour of the entire "collective" of atoms.
The results were published in the Journal of the American Chemical Society and are already being regarded as a reliable guide for the systematic search for new magnetic quasicrystals and their approximants.
