Advanced & Functional Materials
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ThMn12 Sm-Fe-Co permanent magnets
ThMn12 Sm-Fe-Co permanent magnets
Can coercivity at 150 °C in Sm(Fe,Co)11(Ti,V) be predicted within 2 kOe by composition alone, or do twin density and grain size determine the loss?
THE QUESTION
Across ThMn12-type rare-earth-lean Sm-Fe-Co compositions with V/Ti substitution, can coercivity at 150 C be predicted within 2 kOe — the property that decides dysprosium-free viability?
WORK ORDER
Coercivity at 150 °C, twin density, grain size and anisotropy field in melt-spun Sm(Fe1−xCox)11(Ti1−yVy)
BACKGROUND
What this Apodex Lab is
High-temperature electric traction motors require permanent magnets that retain resistance to demagnetisation under thermal load, a requirement currently met by neodymium-iron-boron alloys enriched with scarce dysprosium. Iron-rich ThMn12-type samarium compounds, such as SmFe11Ti substituted with cobalt, offer a pathway that eliminates heavy rare earths. Their intrinsic magnetic figures match incumbent materials: anisotropy fields reach 10–12 T, cobalt substitution raises saturation magnetisation to roughly 1.5–1.6 T, and Curie temperatures exceed 700 K. However, bulk coercivity in synthesized specimens falls far below these theoretical limits, leaving open whether dysprosium-free compositions can reliably sustain the 15–20 kOe coercivity required at 150 °C.
The core obstacle is that existing coercivity measurements come from disparate thin films, melt-spun ribbons, and small ingots prepared by different synthesis routes. As a result, alloy chemistry and microstructure have remained confounded. Cobalt additions alter the twin-formation energy, twin-boundary density, and grain size in Sm(Fe,Co)(Ti,V) alloys, meaning composition can govern coercivity through defect populations rather than intrinsic crystal anisotropy alone. Because twin density, grain size, anisotropy field, and coercivity at 150 °C have never been measured on a single, controlled series of specimens, the available data cannot establish whether coercivity at 150 °C is predictable from composition alone within 2 kOe.
The ThMn12 Sm-Fe-Co permanent magnets Apodex Lab evaluates 24 melt-spun and annealed ribbon specimens alongside aligned powder sets across cobalt fractions of x = 0, 0.15, 0.30 and titanium-to-vanadium ratios of y = 0, 0.5. By measuring coercivity at 150 °C, anisotropy fields, twin-boundary length densities, grain sizes, and α-(Fe,Co) fractions on the same specimen series, the work quantifies the residual error left behind by composition-only predictive models. If microstructural defect metrics reduce this residual below 1 kOe, magnet manufacturers can move away from pure composition screening and redirect development programmes toward processing controls that govern twin formation.
WHY NOW
Why the field is spending on an assumption
Rare-earth-lean Sm-Fe-Co compounds with ThMn12 structures match the intrinsic magnetisation of neodymium-based magnets, but their bulk coercivity falls far short. Existing coercivity data come from room-temperature tests across disparate processing routes, confounding composition with microstructure. A 2024 study shows that cobalt substitution alters twin-formation energy, twin density and grain size, suggesting high-temperature magnetic loss proceeds through defect populations rather than intrinsic anisotropy alone. Published studies also disagree on whether titanium or vanadium stabilisers best resist this degradation. Because twin density, grain size, anisotropy field and coercivity at 150 °C have never been measured on a single matched specimen series, whether coercivity loss is a composition or processing problem remains unresolved.
WHAT WE’D BUY
What we would ask a laboratory to run
We are not buying the answer. We are buying a measurement with an interval — and the bars it will be compared against.
The order commissions the fabrication and testing of 24 melt-spun ribbon specimens across six Sm(Fe1−xCox)11(Ti1−yVy) compositions (x = 0, 0.15, 0.30; y = 0, 0.5) annealed at 800 °C and 900 °C, alongside six aligned powder sets. Measurements quantify coercivity at 25 °C and 150 °C to a repeatability standard deviation of 0.2 kOe or better, saturation magnetisation, anisotropy field, grain size, and twin-boundary length density. The analysis returns the root-mean-square residual of coercivity at 150 °C from a composition-only fit alongside its 95% confidence bounds (0.76× to 1.48× the point estimate), the residual after adding microstructural covariates with its nested-model p-value, and the partial slope of coercivity loss against twin-boundary length density targeted to a 95% confidence interval half-width of 0.15 kOe per µm⁻¹.
SCOPE & LIMITS
Results apply directly to melt-spun and annealed ribbons, whose grain sizes and boundary chemistry serve as a single-route surrogate that may differ from hot-compacted or sintered bulk magnets.
WHO EXECUTES
The kind of lab that can run this
A magnet-alloy synthesis and characterization core facility (university or CRO) with arc melting, melt spinning and sintering capability, high-temperature vibrating-sample magnetometry or a permeameter rated to at least 200 °C, and TEM/EBSD microscopy for twin-density and grain-size metrology.
EXECUTOR KIND
wet-lab
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