The study was led by Assistant Professor Farid Labib of the Research Institute for Science and Technology at Tokyo University of Science, together with Associate Professor Kazuhiro Nawa of the Institute of Multidisciplinary Research for Advanced Materials at Tohoku University and Professor Ryuji Tamura of Tokyo University of Science. The team focused on Tsai-type compounds, a class of multi-shell cluster-based structures in which moment-bearing rare-earth atoms occupy an icosahedral site. In these materials, nested atomic shells, including the rhombic triacontahedron, icosidodecahedron, icosahedron, dodecahedron, and an inner tetrahedron, build up a cluster architecture whose rare-earth icosahedral shell carries the magnetic moments responsible for the compounds’ magnetic response.

Historically, materials chemists have relied on chemically tunable parameters to organize the magnetic properties of complex intermetallics. The most influential of these is the valence-electron concentration, commonly expressed as the electron-per-atom, or e/a, ratio. In metallic systems such as Heusler alloys and approximant crystals, the e/a ratio has been widely used to classify magnetic ground states. In gold-based Tsai-type approximant crystals specifically, the e/a ratio was found to control whether the compounds developed long-range antiferromagnetic order, long-range ferromagnetic order, or a spin-glass state in which the magnetic moments freeze in random orientations. But the predictive power of e/a has a serious limitation: it does not transfer cleanly across different alloy families and constituent elements.

That limitation matters because quasicrystal-based intermetallics are considered promising platforms for exploring emergent magnetic phenomena and quantum states not found in ordinary periodic crystals. Without a reliable, experimentally accessible parameter to guide the search, researchers have lacked a systematic way to identify which compositions are worth synthesizing. As Dr. Labib explained, quasicrystals are among the most uniquely structured materials discovered to date and are expected to exhibit novel magnetic states and quantum phenomena not found in ordinary crystals, yet until now there has been no unified guideline for systematically exploring these phenomena in quasicrystals and their approximant crystals.

To close that gap, the team synthesized a family of gold-based 1/1 approximant crystals containing aluminum or gallium and the rare-earth elements terbium, dysprosium, and holmium, and then systematically measured their structural and magnetic properties. Approximant crystals are periodic structures whose local atomic environments closely mimic those of true quasicrystals, making them experimentally tractable stand-ins for the quasiperiodic originals. The measurements revealed a nearly monotonic inverse correlation between the e/a ratio and the lattice parameter, meaning that as the electron concentration per atom rises, the physical size of the cubic unit cell shrinks in a regular, predictable way.

The researchers then extended their experiments to non-Heisenberg Tsai-type compounds containing terbium, dysprosium, and holmium. These compounds are called non-Heisenberg because their magnetic moments do not behave as simple, freely rotating spins; instead, the crystal electric field generated by the surrounding lattice imposes strong uniaxial magnetic anisotropy that favors specific orientations of the moments. Under these conditions, the team observed characteristic whirling antiferromagnetic and ferromagnetic orders, in which the constrained moments arrange themselves in swirling patterns dictated by the interplay of anisotropy and the conduction-electron-mediated interactions between rare-earth moments on the icosahedral shell.

When the researchers plotted the magnetic ground states against the lattice parameter, the result was striking. The compounds organized with high accuracy according to the size of the unit cell, whereas the conventional e/a classification showed systematic shifts depending on which rare-earth element was present and what the alloy composition was. The phase boundaries were sharply defined. Compounds with lattice parameters above approximately 14.72 angstroms adopted the whirling antiferromagnetic state. Those with lattice parameters between 14.62 and 14.72 angstroms became whirling ferromagnets. And those with lattice parameters below approximately 14.62 angstroms froze into spin-glass states. These well-defined thresholds establish the lattice parameter as a unified and experimentally accessible structural descriptor for predicting magnetic ground states in the Tsai-type family.

The physical interpretation is that structural length scales, alongside electron concentration, must be explicitly considered when understanding the conduction-electron-mediated magnetic interactions in these complex alloys. In rare-earth intermetallics, the magnetic moments communicate with one another indirectly through the conduction electrons, and the strength and sign of that communication depend sensitively on the distances between the moment-bearing atoms. A change in the lattice parameter therefore directly reshapes the geometry of the magnetic interaction network on the icosahedral shell, which in turn determines whether the system settles into antiferromagnetic whirling, ferromagnetic whirling, or glassy freezing. The e/a ratio captures part of this physics but conflates it with element-specific electronic effects, which is why it fails to produce a single, element-independent classification.

The practical implications extend well beyond classification. Because the lattice parameter can be tuned through alloy composition and measured with routine structural characterization, it offers materials designers a direct control knob for targeting a desired magnetic ground state. Dr. Nawa noted that the unified magnetic phase diagram constructed in the study can serve as a practical roadmap for the systematic exploration of new magnetic quasicrystals and approximant crystals exhibiting novel magnetic orders and quantum phenomena, and that it can provide a guideline for designing new magnetic materials with targeted magnetic ground states, opening new opportunities for discovering unconventional magnetism in quasiperiodic and complex intermetallic systems.

The study was supported by the Japan Society for the Promotion of Science through multiple Grants-in-Aid for Scientific Research, by the Murata Science and Education Foundation, and by the Japan Science and Technology Agency through its CREST program. The authors declared no competing interests. For a field that has spent decades cataloguing the exotic magnetism of quasiperiodic materials one compound at a time, the message of this work is unusually clean: in the Tsai-type family, the size of the atomic cage appears to decide the fate of the spins inside it. If the lattice-parameter thresholds hold across further alloy families, the search for new magnetic quasicrystals may become far less of a treasure hunt and far more of an engineering exercise, with the next generation of unconventional magnets designed first on paper, in angstroms.

Subject of Research: Lattice-parameter control of magnetic ground states in Tsai-type quasicrystals and approximant crystals

Article Title: Lattice parameter as a unified parameter governing magnetic ground states in Tsai-type compounds

Article References: Lattice parameter as a unified parameter governing magnetic ground states in Tsai-type compounds. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: quasicrystals, Tsai-type clusters, lattice parameter, magnetic ground states, antiferromagnetism, ferromagnetism, spin glass, rare-earth intermetallics, electron-per-atom ratio, magnetic anisotropy, approximant crystals, Tokyo University of Science

The challenge has always been the gap between making the material and making it usable. Quasicrystals in aluminum alloys form only when molten metal cools extremely rapidly, which is why the starting materials are usually produced as fine powders by gas atomization. In that process, a stream of molten alloy is broken into droplets and solidified at rates high enough to trap the icosahedral quasicrystalline phase, known as I-phase, in a nanocomposite structure of quasicrystal dispersoids embedded in an aluminum matrix. Turning those powders into a solid engineering component, however, normally requires elevated temperatures and long holding times, exactly the conditions that allow the metastable quasicrystals to transform into equilibrium phases and destroy the microstructure that gives the alloy its special properties.

Spark plasma sintering, or SPS, has emerged as a promising way to bridge that gap. In SPS, a pulsed electric current passes through a conductive die and the powder compact itself, while a uniaxial pressure is applied simultaneously. The result is very rapid heating, short cycle times and low overall process temperatures, all of which suppress the diffusion-controlled transformations that would otherwise consume metastable phases. The technique has been used before to consolidate quasicrystal-forming alloys, but until now no study had reported achieving full density in an aluminum-quasicrystal composite while completely preventing decomposition of the quasicrystalline phase. That is the milestone the Connecticut team set out to reach.

The researchers worked with gas-atomized powders of an Al-Cr-Co-Mn-Zr alloy, a composition developed in a series of earlier studies on icosahedral-phase-strengthened aluminum. The powders displayed the desired nanocomposite structure: fine icosahedral quasicrystals dispersed throughout an aluminum matrix. The team consolidated the powders using SPS under an applied pressure of 100 megapascals at temperatures ranging from 350 to 600 degrees Celsius, then examined the resulting microstructures with X-ray diffraction and electron microscopy to determine exactly what happened to the quasicrystals at each processing condition.

The results revealed a sharp transition. Samples sintered at 350 degrees Celsius retained their quasicrystals but remained porous, meaning the powder particles had not bonded into a fully dense solid. At 400 degrees Celsius and above, the compacts densified, but the quasicrystals began to decompose, transforming into coarse equilibrium phases identified as Al45(Cr,Mn)7 and Al9Co2. By 600 degrees Celsius the transformation was complete, leaving a dense but ordinary material that had lost the nanocomposite character of the starting powder. Using X-ray diffraction and electron microscopy, the team pinpointed 400 degrees Celsius as the onset temperature for quasicrystal decomposition under these processing conditions, defining a narrow and unforgiving processing window.

That window posed a dilemma: densification seemed to require temperatures that destroyed the very phase the researchers wanted to keep. Their solution was to change the other processing variable. Instead of raising the temperature, they raised the pressure. In a second set of SPS trials conducted at just 375 degrees Celsius, below the decomposition threshold, the team applied higher pressures than in the first campaign. The additional pressure provided the driving force needed to close the remaining porosity through plastic deformation and creep of the aluminum matrix, mechanisms well documented in field-assisted sintering of metals, without ever pushing the quasicrystals past their thermal limit.

The strategy worked. The samples sintered at 375 degrees Celsius under higher pressure reached full density while retaining the quasicrystalline phase completely, with no detectable decomposition. Microscopy confirmed that the fine icosahedral dispersoids survived intact in the aluminum matrix, preserving the nanocomposite architecture of the gas-atomized powder. Remarkably, this fully dense, quasicrystal-retaining material also exhibited the highest hardness of any sample in the study, measuring 164.8 plus or minus 3.8 HV. The combination of full densification, complete phase retention and maximum hardness in a single sample demonstrates that the pressure-temperature trade-off can be exploited to beat the kinetics of decomposition entirely.

The significance extends beyond one alloy system. Aluminum-quasicrystal composites are attractive for tribological applications such as wear-resistant coatings and components, and related quasicrystal-strengthened alloys have been explored for additive manufacturing, cold spray deposition and other powder-based processing routes. In each of these contexts, the metastable quasicrystals face the same threat: any thermal exposure during consolidation or deposition can degrade them. The new results show that by carefully balancing pressure against temperature, and by exploiting the rapid heating and short cycle times inherent to SPS, it is possible to consolidate metastable-phase composites to full density without sacrificing the microstructure that makes them valuable. The authors connect the observed microstructures and hardness values to the densification mechanisms operating during SPS processing, providing a mechanistic framework that other groups can apply to their own metastable systems.

The work also fits into a broader effort at the University of Connecticut to understand and exploit icosahedral-phase-strengthened aluminum alloys, spanning gas atomization, thermal stability studies, laser powder bed fusion and additive friction stir deposition. By establishing a processing route that preserves I-phase through the most thermally demanding step, bulk consolidation, the study closes a critical link in that chain. For a class of materials whose defining feature is an atomic arrangement that nature rarely allows at equilibrium, the message is clear: with the right combination of heat, pressure and speed, even the most fragile order can be coaxed into a dense, durable and remarkably hard bulk solid.

Subject of Research: Spark plasma sintering of aluminum-quasicrystal nanocomposites to retain the metastable icosahedral I-phase

Article Title: Retention of I-phase during spark plasma sintering of aluminum-quasicrystal nano-composites

Article References: Yavas, B., Jenabi, A., Rommel, S., Benson, C. L., Aindow, M., & Dupuy, A. D. (2026). Retention of I-phase during spark plasma sintering of aluminum-quasicrystal nano-composites. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13812-7

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13812-7

Keywords: quasicrystals, spark plasma sintering, aluminum alloys, nanocomposites, icosahedral phase, gas atomization, metastable phases, powder metallurgy, hardness, wear resistance, Al-Cr-Co-Mn-Zr, densification