To appreciate why these numbers matter, it helps to understand what soft magnetic composites actually do. Unlike the laminated silicon steel stacks found in large transformers, soft magnetic composites are made from insulated metallic powder particles pressed into a solid bulk. The insulating coating between particles suppresses eddy currents, which are circulating electrical losses that grow punishingly severe as operating frequencies climb into the megahertz range. That makes these composites natural candidates for the miniaturized inductors, power chokes, and high-frequency converters that sit at the heart of electric vehicles, fast chargers, data-center power supplies, and next-generation wireless power systems. As engineers push devices to switch faster and shrink further, the magnetic materials inside them must deliver high magnetization, high permeability, and minimal energy loss all at once, a triple demand that has proven remarkably difficult to satisfy simultaneously.

Iron-based amorphous alloys are among the most promising starting points. Because their atoms are frozen in a disordered, glass-like arrangement rather than a periodic crystal lattice, they lack the crystalline anisotropy that normally resists magnetization reversal, giving them intrinsically low coercivity and low core loss. Yet the very processing route that turns amorphous powders into usable components undermines these advantages. Amorphous powders deform poorly under pressure, so when they are cold-compacted into a core, tiny air gaps remain between particles. These gaps weaken the magnetic coupling across particle boundaries, which drags down the effective permeability of the finished component. Engineers can raise the compaction pressure to squeeze out the gaps, but that remedy introduces its own poison: internal stresses and defects that pin magnetic domains in place, raising coercivity and hysteresis loss. The result is a frustrating seesaw in which improving one property degrades another.

Conventional nanocrystallization has been the field’s standard answer to this dilemma. By carefully annealing amorphous alloys, researchers encourage the growth of nanometer-scale crystalline grains whose size and distribution can be tuned to enhance magnetic softness. Decades of work on alloys such as Finemet-style compositions have shown that grains of just the right dimension can lower anisotropy and improve permeability. But even this sophisticated approach struggles to balance all the competing requirements at once, because grain growth consumes the amorphous matrix, alters saturation magnetization, and can introduce new sources of loss. What the field has lacked is a simpler microstructural strategy, one that decouples the optimization of surface and bulk properties and can be applied without wholesale restructuring of the material.

The Chinese team’s answer is to intervene at a scale below conventional nanocrystallization entirely. In their process, amorphous soft magnetic powder is exposed to a high-energy argon and oxygen plasma before conventional cold compaction. The plasma does not merely clean or roughen the surface; it drives chemical and structural transformations in a thin surface layer of each particle. The result is the formation of ultrafine precipitates of four distinct phases: alpha-iron, magnetite, silicon dioxide, and hematite, all with dimensions of only 0.8 to 2.5 nanometers and all dispersed within the surface region of the amorphous powders. Crucially, the bulk composition of the powder remains untouched, meaning the plasma acts as a controllable surface-modification tool rather than a global alteration of the alloy.

These supranano precipitates perform a subtle but decisive magnetic function. In a ferromagnetic material, magnetization changes direction through the reversal of magnetic moments, a process that typically begins at sites where the energy landscape favors nucleation of a reversed domain. The researchers found that their supranano precipitates act as preferential nucleation sites for exactly this magnetic-moment reversal. Rather than forcing domain walls to fight their way through a homogeneous glassy matrix, the precipitates provide ready footholds from which reversal can spread, facilitating magnetization reversal and substantially reducing the field needed to demagnetize the material. That is the physical origin of the strikingly low coercivity of 0.13 oersted, and because coercivity governs hysteresis loss, it cascades directly into the material’s exceptional low-loss performance at megahertz frequencies.

The full property set reported in the study reads like a wish list for power-electronics engineers. An effective permeability of 37.3 indicates that the composite concentrates magnetic flux efficiently despite the inevitable air gaps of powder metallurgy. A saturation magnetization of 185 emu per gram means the material can carry a large magnetic load before saturating, supporting compact component designs that handle substantial power. And a core loss of 191.18 kilowatts per cubic meter at 1 megahertz and 20 millitesla represents the kind of ultralow dissipation that keeps components cool and efficient in demanding switching applications. The significance lies not in any single figure but in their coexistence: the plasma treatment improved magnetic softness without sacrificing the magnetization and permeability that other strategies typically trade away.

The study, led by Jiwei Lv, Haibo Ke, and Chao Yang together with colleagues including Zhicheng He, Weisi Cai, Hongwei Ma, Tao Song, Pengxu Li, Luoxuan Hu, Liuzhang Ouyang, Min Zhu, and Weihua Wang, was recently published online in Materials Futures, an international journal covering interdisciplinary materials science research. The work introduces supranano multi-precipitate engineering as a distinct concept in microstructural design, one that operates beneath the grain-size regime that has dominated magnetic materials research for decades. Because the plasma treatment modifies only the powder surface while leaving the bulk composition intact, the authors note that it may integrate readily into existing powder-processing workflows, a practical consideration that often determines whether laboratory breakthroughs ever reach factory floors.

Looking forward, the team plans to tackle the scalability of plasma-assisted processing, the perennial challenge that separates elegant laboratory demonstrations from industrial reality. They also intend to extend the supranano precipitate concept to related techniques, including plasma-assisted ball milling, which could combine mechanical alloying and surface activation in a single step to further optimize microstructure and magnetic performance. If those efforts succeed, the implications extend across the electronics landscape. High-frequency inductors, power chokes, and other miniaturized magnetic components built from such composites could shrink power converters, cut energy waste in everything from electric drivetrains to server farms, and ease the thermal constraints that currently limit how densely power electronics can be packed. In a world hungry for efficient electrification, engineering matter at less than three nanometers may prove to be one of the most consequential tricks in the materials science playbook.

Subject of Research: Plasma-engineered supranano precipitates in amorphous soft magnetic composites for high-frequency power electronics

Article Title: Beyond conventional nanocrystallization: Supranano precipitates advance high-frequency soft magnetic materials

Article References: Beyond conventional nanocrystallization: Supranano precipitates advance high-frequency soft magnetic materials. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: soft magnetic composites, supranano precipitates, amorphous alloys, plasma treatment, coercivity, core loss, permeability, saturation magnetization, high-frequency electronics, nanocrystallization, magnetic-domain reversal, power electronics

A new study published in the Journal of Materials Science by Ester Kelly Starick Pellegrino and colleagues at the University of São Paulo, together with collaborators at the Federal University of Itajubá and the Federal University of Rio de Janeiro, has now filled that gap. The team constructed a liquidus projection for the cobalt-rich region of the Co-Si-B system, a two-dimensional map that shows which crystalline phases are the first to solidify from the molten alloy across the entire compositional space. This map is far more than an academic exercise. When engineers want to manufacture an amorphous metallic ribbon, they need to know exactly which competing crystalline phases will try to form as the melt cools, because those crystals are the enemies of glass formation and can destroy the delicate amorphous structure that gives the alloy its superior properties.

The logic behind these alloys is elegantly chemical. Amorphous metallic alloys typically contain 70 to 85 atomic percent transition metals, with the remaining 15 to 30 percent made up of metalloids such as silicon and boron. Boron, with its small atomic radius, promotes a denser and more complex liquid structure that hinders the atomic rearrangement needed for boride crystals to nucleate. Silicon works synergistically by increasing the viscosity of the melt and stabilizing the amorphous network against premature devitrification. Together, these metalloids allow molten metal to be rapidly quenched into a homogeneous glassy ribbon rather than a polycrystalline solid. But the glass is metastable, and upon heating it will always try to crystallize into the equilibrium phases. Knowing precisely what those phases are, and at what compositions they dominate, is therefore the foundation of rational alloy design.

To build their map, the researchers first performed a thermodynamic extrapolation using Thermo-Calc software, combining the most recent optimized assessments of the binary Co-Si, Co-B, and Si-B systems and accounting for the known ternary phase. They then synthesized a series of cobalt-rich alloys by arc melting high-purity elements in a water-cooled copper crucible under argon. Each composition was remelted four times to guarantee chemical homogeneity, with total mass losses kept below one percent so that the nominal compositions could be trusted as the true alloy compositions. The as-cast samples were then interrogated with an arsenal of characterization techniques: X-ray diffraction, scanning electron microscopy with backscattered electron imaging, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction, the latter used to definitively identify crystal phases in the microstructures.

The resulting liquidus projection identifies ten primary precipitation fields, meaning ten different crystalline phases that can be the first to appear as the liquid cools, depending on composition. These include the cobalt solid solution in its high-temperature and room-temperature allotropic forms, the silicides Co3Si, alpha Co2Si, beta Co2Si, and CoSi, the borides Co3B, Co2B, and CoB, and the ternary phase Co4.75Si2B. The map also traces the monovariant lines, the boundaries along which two phases crystallize simultaneously from the melt, and proposes nine ternary invariant reactions involving the liquid phase, including three ternary eutectic points where three phases solidify together. Twelve binary invariant reactions inherited from the Co-Si and Co-B edge systems anchor the projection, and the arrows along the monovariant lines point the way toward lower temperatures, tracing the solidification paths that molten alloys of any given composition will follow.

Perhaps the most striking finding concerns the ternary phase Co4.75Si2B, first identified in the literature more than sixty years ago but never before characterized in terms of its melting behavior. By preparing an alloy with exactly the stoichiometric composition of this phase, the researchers discovered that it does not melt congruently. Instead, the microstructure showed crystals of Co4.75Si2B enveloping primary grains of alpha Co2Si, a classic signature of a peritectic reaction. In other words, the ternary phase forms when the liquid reacts with pre-existing alpha Co2Si crystals rather than crystallizing directly from the melt on its own. This single observation, expressed as the reaction L plus alpha Co2Si yielding Co4.75Si2B, resolves a long-standing question about the phase and reshapes the topology of the entire liquidus surface around it.

Equally fascinating is the discovery of three thermal maxima along the monovariant lines, labeled m1, m2, and m3. These points act as thermodynamic watersheds on the liquidus surface. On one side of a maximum, the liquid composition evolves toward one ternary eutectic point during solidification; on the other side, it flows toward a completely different one. The researchers demonstrated this with pairs of alloys whose compositions straddled the maxima: alloy 41, for example, saw its liquid become richer in boron as it solidified toward the EI eutectic, while alloy 5a, on the opposite side of maximum m2, saw its liquid become richer in cobalt and terminate along a different monovariant line. Tiny shifts in the initial composition, therefore, send the solidification process down entirely different trajectories, a fact of enormous practical importance for anyone trying to control the microstructure of a cast or rapidly quenched alloy.

The monovariant line separating the alpha Co2Si and Co4.75Si2B primary fields turned out to have a dual personality. Between the thermal maximum m1 and the invariant point UIII, the line behaves as a eutectic valley, with the two phases crystallizing in a coupled fashion. Between m1 and the invariant point UVI, however, the line switches to peritectic behavior, with one phase reacting with the liquid to form the other. This kind of behavioral switch along a single monovariant line is a subtle feature of ternary phase diagrams, and detecting it required the careful microstructural detective work that characterizes the whole study, including the identification of fine-scale eutectic constituents that push the resolution limits of electron backscatter diffraction to roughly one micrometer.

The new projection is in good agreement with the partial liquidus map proposed by Omori and Hashimoto in 1977 for the region above 66.7 atomic percent cobalt, but it extends and refines that pioneering work substantially, adding fields for phases such as CoSi, CoB, Co3Si, and beta Co2Si that the earlier study could not resolve. The authors note that the actual temperatures of the invariant reactions, liquidus, and solidus were not determined in this study, leaving a clear target for future differential thermal analysis and thermodynamic modeling. Even so, the compositional framework alone provides what the field has lacked: an experimentally grounded prediction of solidification behavior across the cobalt-rich ternary space.

For the growing community working on soft magnetic materials, the implications are immediate. Cobalt-based metallic glasses are prized in high-precision applications where magnetic cores must be stable, efficient, and corrosion-resistant, and every improvement in glass-forming ability translates directly into better ribbons and devices. With the liquidus projection now in hand, alloy designers can anticipate which borides and silicides will compete with glass formation for any candidate composition, choose compositions that maximize the distance from troublesome primary phase fields, and understand why small compositional tweaks near the thermal maxima can dramatically alter the outcome of rapid solidification. It is a reminder that even in a field as mature as metallurgy, fundamental maps still hold the power to unlock the next generation of technology, one carefully melted button of alloy at a time.

Subject of Research: Phase equilibria and solidification behavior of the cobalt-rich Co-Si-B ternary alloy system

Article Title: Liquidus projection of the cobalt-rich Co–Si–B system

Article References: Pellegrino, E. K. S., Boas, S. B. V., da Silva, A. A. A. P., Ferreira, L. M., Faria, M. I. S. T., Coelho, G. C., & Nunes, C. A. (2026). Liquidus projection of the cobalt-rich Co–Si–B system. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13756-y

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13756-y

Keywords: metallic glasses, amorphous alloys, cobalt alloys, liquidus projection, phase diagrams, peritectic reaction, ternary system, solidification, magnetic materials, silicides, borides, thermodynamics