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

The material at the heart of the study is alpha double-prime iron nitride, Fe16N2, an ordered tetragonal phase that has fascinated magnet researchers for decades. It is made entirely of abundant, inexpensive elements, yet it boasts a theoretical saturation magnetization of roughly 290 emu per gram and a magnetocrystalline anisotropy near 1.0 times ten to the seventh erg per cubic centimeter, figures that rival or exceed those of many rare-earth compounds. The catch has always been coercivity, the field required to demagnetize the material, which determines whether a magnet can actually hold its grip in a motor. Powders of Fe16N2 made by scalable methods have historically shown coercivities too low for demanding applications, and closing that gap has become one of the central challenges in the search for supply-chain-proof permanent magnets.

The physics of the problem is well understood. Coercivity in ferromagnetic particles rises as particle size shrinks toward the single-domain limit, which for Fe16N2 sits at roughly 73 nanometers. That insight has driven a generation of bottom-up synthesis efforts, from coprecipitation to hydrothermal routes, all aimed at producing nanoscale iron oxide precursors that can later be reduced to iron and nitrided with ammonia. The trouble is that oxide nanoparticles love to agglomerate and coarsen during hydrogen reduction, destroying the fine features that made them attractive in the first place. The original size and shape of the nanoparticles are rarely preserved, and the resulting nitride inherits a compromised microstructure and a disappointingly low coercivity.

Aerosol-assisted synthesis offers an appealing way out because it produces micrometer-scale particles that resist coarsening while remaining compatible with continuous, high-throughput manufacturing. Previous studies explored salt-assisted porosity and hollow particle structures to aid nitridation, but the coercivities reported for aerosol-derived Fe16N2 powders remained modest, generally between 1.2 and 1.47 kilooersted. Most of that work focused on raising the fraction of the magnetic Fe16N2 phase rather than on engineering the particle microstructure itself. The new study, published in Advances in Industrial and Engineering Chemistry by researchers at the Korea Institute of Materials Science together with a collaborator from Hyundai Motor Company, takes the opposite approach: keep the chemistry of the final conversion steps identical, and instead vary the microstructure of the oxide precursor at the very start of the process.

The team prepared three distinct hematite, alpha-Fe2O3, precursors using two aerosol techniques and two different iron salts. The first route was ultrasonic spray pyrolysis, in which a 0.1 molar solution of iron nitrate was nebulized at 1.7 megahertz and carried by compressed air through a quartz tube reactor held at 700 degrees Celsius. Inside the hot zone, each droplet underwent solvent evaporation and thermal decomposition in a single step, yielding solid, spherical hematite particles with smooth, dense surfaces and an average diameter of just 0.5 micrometers. The second route was spray drying, a gentler two-step process in which droplets were atomized with a two-fluid nozzle and dried at only 220 degrees Celsius, leaving intermediate salt particles that were subsequently calcined in air at 450 degrees Celsius for four hours to form the oxide. Spray drying was performed with both iron nitrate and iron oxalate solutions at a much higher solid content of 10 weight percent, producing substantially larger particles, around 3.9 and 4.8 micrometers respectively.

The choice of salt turned out to matter enormously. The spray-dried nitrate powder retained its spherical shape but developed a rough surface of enlarged primary grains as hematite grew during calcination, with an average crystallite size of 31.6 nanometers measured by X-ray diffraction. The oxalate-derived powder, by contrast, emerged with a crumpled, fractured and highly porous texture. The reason lies in the thermal chemistry: iron oxalate decomposes at a higher temperature than iron nitrate, and as it breaks down it releases copious carbon monoxide and carbon dioxide gas that punches fine pores into the particle as it escapes. Because the decomposition happens later under identical calcination conditions, oxide formation is delayed, iron cation diffusion is limited, and grain growth is suppressed, leaving the oxalate-derived hematite with significantly finer crystallites of 20.7 nanometers on average.

All three precursors then passed through exactly the same conversion sequence. Hydrogen reduction at 330 degrees Celsius for four hours transformed the hematite into body-centered cubic alpha iron, and after a brief argon purge the gas flow was switched to ammonia for nitridation at 175 degrees Celsius for fifteen hours, yielding the body-centered tetragonal Fe16N2 phase. X-ray diffraction with whole-pattern profile fitting showed that every sample contained more than 90 weight percent of the desired phase, with the two nitrate-derived powders reaching purities of roughly 94 to 95 weight percent and the oxalate-derived powder coming in at about 90 percent. Remarkably, the final nitride crystallite size converged to a narrow window of 17 to 18 nanometers for all three samples, regardless of the crystallite size in the starting oxide. The researchers attribute this reset to the reduction step itself, in which oxygen removal and iron atom rearrangement govern the formation of new iron crystallites whose size is largely independent of the initial oxide state, while the subsequent low-temperature nitridation preserves that fine structure.

Electron microscopy revealed that the distinctive personalities of the three precursors survived the entire journey. The spray-pyrolyzed particles stayed as smooth spheres of about half a micrometer, merely roughened at the surface. The spray-dried nitrate particles shrank from 3.9 to 2.7 micrometers as oxygen left the lattice and kept their rough, porous surfaces. The oxalate-derived particles shrank only slightly, from 4.8 to 4.5 micrometers, but their porosity intensified during reduction and nitridation, producing a labyrinth of pore walls, edges and rough surfaces. Most of this architectural change occurred during hydrogen reduction, when vacancies and voids formed as oxygen was stripped away, while the low-temperature nitridation made only minimal further alterations. In effect, the microstructure engineered at the oxide stage was faithfully transmitted to the final magnetic powder.

The magnetic measurements delivered the study’s punchline. With crystallite size and phase purity held nearly constant across the three samples, coercivity varied systematically and dramatically: 1.14 kilooersted for the spray-pyrolyzed nitrate powder, 1.46 kilooersted for the spray-dried nitrate, and 1.86 kilooersted for the spray-dried oxalate. Because coercivity in iron nitride materials generally rises with Fe16N2 fraction, the fact that the least pure sample showed the highest coercivity rules out phase purity as the explanation, and the uniform crystallite size rules out that variable as well. The team points instead to domain-wall pinning, the mechanism by which defects, grain boundaries and surface irregularities impede the movement of magnetic domain walls and make the material harder to demagnetize. The oxalate-derived particles, with their abundant pore walls, edges and rough surfaces, simply offered far more pinning sites than their smooth-surfaced cousins. Notably, both spray-dried powders exceeded the 1.2 kilooersted recently achieved with salt-assisted spray pyrolysis, and they did so without any sacrificial templates or added process steps.

The trade-offs are honest and instructive. The high-coercivity oxalate powder showed a saturation magnetization at 2.5 tesla of about 153 emu per gram, lower than the roughly 190 and 185 emu per gram of the nitrate-derived samples, a consequence of its highly porous morphology reducing the density of magnetic material per unit volume alongside its slightly lower phase fraction. Even so, the study demonstrates something potentially transformative for magnet manufacturing: coercivity, the property that has most stubbornly resisted improvement in scalable iron nitride synthesis, can be tuned simply by choosing the aerosol route and the precursor salt. Spray pyrolysis and spray drying are both continuous, industrially mature processes that operate on gram-per-hour scales today, and the entire workflow, from dissolved iron salt to nitrided magnetic powder, involves nothing but water, air, hydrogen and ammonia. For a field racing to build high-performance magnets without rare earths, the message is that the path to a better magnet may begin not in the final nitridation furnace but in the microscopic architecture of a particle of rust.

Subject of Research: Aerosol synthesis and precursor microstructure control to enhance coercivity in rare-earth-free alpha double-prime Fe16N2 magnetic powders

Article Title: Scalable aerosol routes to enhance coercivity in α′′-Fe16N2 powders through α-Fe2O3 microstructure control

Article References: Jeong, J., Park, H. J., Koo, H. Y., Kim, D., Lee, J.-G., & Baek, Y.-K. (2025). Scalable aerosol routes to enhance coercivity in α′′-Fe16N2 powders through α-Fe2O3 microstructure control. Advances in Industrial and Engineering Chemistry, 1(1), Article 23. https://doi.org/10.1007/s44405-025-00026-9

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00026-9

Keywords: Fe16N2, rare-earth-free magnets, coercivity, aerosol synthesis, spray pyrolysis, spray drying, hematite precursor, iron nitride, domain-wall pinning, permanent magnets, microstructure control, hydrogen reduction

Researchers led by Kangmo Koo and Jimin Lee, working with Young-Tae Kwon of the Korea Institute of Materials Science and Yong-Ho Choa of Hanyang University, report in Advanced Composites and Hybrid Materials a soft actuator built from ultrafine particles of samarium-iron-nitride, Sm2Fe17N3, that keeps working reliably at temperatures up to 350 degrees Celsius. For comparison, actuators made from conventional Nd2Fe14B particles suffered severe degradation beyond 200 degrees Celsius. The gap of 150 degrees Celsius is not a marginal improvement; it opens an entirely new operating envelope for magnetic soft machines in environments such as engine bays, industrial furnaces, aerospace structures and minimally invasive medical devices that must survive sterilization.

The reason the field has been stuck with thermal fragility lies in the physics of ferromagnetism. Every ferromagnetic material has a Curie temperature, the point at which thermal energy overwhelms the quantum-mechanical exchange interactions that align atomic magnetic moments, and the material loses its permanent magnetization. Nd2Fe14B, despite holding the highest maximum energy product of any commercial permanent magnet, has a relatively modest Curie temperature, and even well below that point its coercivity, the field needed to demagnetize it, drops rapidly with heat. In a soft actuator, the embedded particles must retain their remanent magnetization to experience torque in an applied field; once heat erodes that magnetization, the programmed deformation collapses and the device simply stops working.

Samarium-based magnets have always been the obvious alternative. Sm2Fe17N3 combines a high Curie temperature with large magnetocrystalline anisotropy, the intrinsic property that anchors magnetization against reversal and gives the material high coercivity. The compound also offers strong remanent magnetization and a competitive energy product, making it a candidate to match the performance of neodymium magnets while shrugging off heat that would cripple them. The problem has been making it in the right form. High-performance magnetic composites need fine, uniform particles so they can be dispersed evenly in elastomers and magnetized into intricate patterns; coarse or irregularly shaped particles produce weak spots, rough surfaces and unpredictable actuation.

Synthesizing ultrafine Sm2Fe17N3 has proved notoriously difficult. The conventional route runs through a reduction-diffusion process, in which samarium oxide is reduced in the presence of iron and calcium, allowing samarium atoms to diffuse into the iron lattice to form the Sm-Fe intermediate phase, which is subsequently nitrogenated. At the fine particle sizes the field needs, the samarium species tend to migrate and coarsen aggressively, producing overgrown Sm-Fe intermediate phases that ruin the uniformity of the product. The result has historically been powders that are either too coarse for high-quality composites or too chemically heterogeneous to deliver the intrinsic magnetic performance the compound promises.

The team’s solution is an elegant materials-chemistry trick: a calcium oxide core-shell strategy. By engineering a CaO shell around the reacting particles, the researchers created a physical barrier that suppresses the overgrowth of the Sm-Fe intermediate phase during reduction-diffusion. The shell confines the diffusion pathway, so each particle transforms uniformly rather than cannibalizing its neighbors. After nitrogenation, the process yields ultrafine Sm2Fe17N3 particles with systematically enhanced magnetic properties. The measured intrinsic coercivity reached 12.59 kilo-oersted, and both the remanent magnetization and the maximum energy product improved markedly relative to control samples made without the CaO shell. That combination matters because an actuator needs high coercivity to survive heat and demagnetizing fields, but it also needs strong remanence and energy product to generate large forces and large bending deformations.

With the ultrafine particles in hand, the researchers embedded them in elastomer matrices and programmed the magnetization profiles needed for shape-morphing soft actuators. When they drove the devices under elevated temperature, the Sm2Fe17N3 composites maintained robust actuation all the way to 350 degrees Celsius, while otherwise comparable Nd2Fe14B-based actuators showed severe degradation beyond 200 degrees Celsius. The demonstration effectively redefines the thermal ceiling of magnetoactive soft robotics, replacing the neodymium workhorse with a samarium alternative that no longer has to be babied away from heat.

The implications stretch well beyond the laboratory bench. Soft actuators built on this material could operate inside industrial machinery, near combustion engines or within thermal processing equipment, where untethered magnetic control was previously impractical. In aerospace, magnetic soft structures that survive thermal cycling could enable adaptive surfaces and deployable mechanisms without the servo motors and wiring that add weight and failure points. In medicine, instruments that must endure autoclave sterilization at elevated temperatures could retain full magnetic functionality afterward. The core-shell synthesis strategy itself may also generalize: if a sacrificial oxide shell can tame diffusion during reduction-diffusion in samarium magnets, similar approaches could refine other hard-magnetic or reactive compounds where fine particle synthesis has been blocked by coarsening.

There are still engineering questions ahead. Scaling the CaO core-shell process from laboratory batches to tonnage production, integrating the ultrafine powders into existing composite fabrication workflows, and optimizing elastomer matrices so they survive the same 350-degree environments as the particles will all demand further work. But the central result stands on its own: the thermal limit that has constrained hard-magnetic soft actuators since their inception is not a law of nature but a limitation of one particular magnet. By combining a carefully engineered synthesis route with a magnetically superior compound, the team has shown that soft machines can be programmed with magnetic fields and still take the heat. For a field whose ambitions run from microsurgery to space exploration, that is a genuine step change.

Subject of Research: Development of thermally stable ultrafine Sm2Fe17N3 magnetic particles for high-temperature soft actuators

Article Title: Ultrafine Sm2Fe17N3 soft actuators enabling robust operation at elevated temperature

Article References: Ultrafine Sm2Fe17N3 soft actuators enabling robust operation at elevated temperature. (n.d.). https://doi.org/10.1007/s42114-026-02082-1

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02082-1

Keywords: Sm2Fe17N3, soft actuators, hard-magnetic soft composites, Nd2Fe14B, thermal stability, coercivity, CaO core-shell strategy, reduction-diffusion process, soft robotics, magnetic materials, Curie temperature, elevated temperature actuation