Science1 publisher2 min readPublished
Lattice spacing sorts magnetic order in gold-based Tsai alloys more cleanly than electron count
Japanese chemists say lattice spacing, with cutoffs at 14.62 and 14.72 angstroms, sorts gold-alloy magnetism better than electron count. That gives chemists looking for new magnetic quasicrystals one measurable target, as long as a new alloy's spacing can be predicted from its composition.
The Scientist · Science desk
What happened
- Farid Labib and Ryuji Tamura of Tokyo University of Science and Kazuhiro Nawa of Tohoku University asked whether cell size alone could organize magnetic states in Tsai-type compounds.
- The team synthesized a family of Au-(Al/Ga) 1/1 approximant crystals built with terbium, dysprosium and holmium, then measured their structure and magnetism.
- Compounds with the largest cells order as whirling antiferromagnets, those in the middle band as whirling ferromagnets, and those with the smallest cells as spin glasses.
- The study is scheduled for publication in the Journal of the American Chemical Society on Sept. 30, 2026.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- constraint Targeting a ferromagnet demands tight composition control, since a small overshoot in cell size either way yields an antiferromagnet or a spin glass instead.
- constraint The cutoffs are calibrated on three rare-earth elements in one gold-based family, so applying them to other rare earths or other quasicrystal families remains an untested extrapolation.
- decision Groups that classified gold-based Tsai compounds by electron count can re-plot their data against lattice parameter to check whether their element-dependent boundary shifts disappear.
Cell size and electron count move together in these alloys. Across the family, the lattice parameter fell as the electron-per-atom ratio rose, in a nearly monotonic inverse relation [4]. So the result is about which of two linked numbers sorts the phases with fewer exceptions. When the compounds were sorted by e/a, the boundaries between magnetic states shifted systematically with the rare-earth element and the alloy composition. Sorted by lattice parameter, the states fell into place "with high accuracy," according to the phys.org account [5]. The account does not put a number on that accuracy or say how many compounds sit near each cutoff.
I think the likeliest reading is that cell size picks up element-specific offsets that a plain electron count misses. That fits what was already known about e/a in gold-based Tsai-type approximants. The ratio tracks antiferromagnetic, ferromagnetic and spin-glass states there, but its predictive power is limited across alloy families and constituent elements [2].
There is a physical reason spacing could matter. In Tsai-type compounds the rare-earth atom that carries the magnetic moment sits on an icosahedral site inside clusters of nested shells [7]. In these non-Heisenberg compounds of terbium, dysprosium and holmium, the crystal electric field creates a strong uniaxial anisotropy, and the whirling magnetic orders go with it [8]. A smaller cell also comes with a different electron count and a different composition. The sorting therefore shows which number organizes the phases best across samples. It does not show which of those changes switches the order.
The authors present the diagram as a guide for further searches. "Until now, there has been no unified guideline for systematically exploring these novel phenomena in quasicrystals and their approximant crystals," Labib said [9]. Nawa said the phase diagram "can serve as a practical roadmap for systematic exploration of new magnetic quasicrystals and approximant crystals exhibiting novel magnetic orders and quantum phenomena" [10]. He added that it "can also provide a guideline for designing new magnetic materials with targeted magnetic ground states" [12].
The ferromagnetic band is thin. The window between the 14.62 and 14.72 angstrom cutoffs [6] is 0.10 angstrom wide [1], about 0.7 percent of the cell edge [2]. A chemist also measures the lattice parameter only after the crystal exists. To choose a composition in advance, a designer has to predict the spacing it will produce. The most direct way back to composition runs through electron count, whose phase boundaries shift with the element [4] [5].
What to watch
- A gold-based Tsai compound made with a rare-earth element outside terbium, dysprosium and holmium that lands on the predicted side of the 14.62 or 14.72 angstrom cutoff would show whether the thresholds hold beyond the original family.
- An experiment that changes cell size while holding composition fixed, for example under applied pressure, would show whether spacing itself switches the magnetic order.