Specifying a permanent magnet or soft magnetic material in 2026 is a four-way trade between NdFeB's energy density, SmCo's thermal headroom, AlNiCo's stability and ferritic/Si-steel's cost-per-kilogram on AC paths; rare-earth price volatility and IEC 60404-8/60404-9 grade formats continue to reshape the buy.
Process engineers usually anchor on a maximum (BH)max window of roughly 30-52 MGOe for sintered NdFeB, 18-32 MGOe for bonded NdFeB, 16-32 MGOe for 2:17 SmCo, 4-9 MGOe for cast AlNiCo and 1-5 MGOe for SrO / BaO hard ferrite, then back-fit Curie temperature, corrosion class and machining tolerance [S1][S3].
NdFeB: the energy-density workhorse, with thermal and corrosion carve-outs
Sintered NdFeB grades (N35-N54 family, plus UH/SH/EH/AH/VH temperature suffixes) deliver the highest room-temperature (BH)max in the family tree, commonly landing in a 33-53 MGOe window with remanence Br of 1.18-1.45 T, while bonded NdFeB sits lower at 6-12 MGOe because the polymer matrix dilutes the magnetic phase [S1].
Standard N-grade Curie temperature is 310-340 °C; the SH/AH/VH suffixes push intrinsic coercivity (Hcj) up to roughly 25-30 kOe and pull continuous-use ceilings toward 200-230 °C, which is the practical ceiling for most traction motors and industrial servo assemblies. Corrosion is the trade: NdFeB reacts in humid / chloride-bearing atmospheres, so surface treatment (Ni-Cu-Ni, Zn, e-coating, polymer, parylene) is not optional. For buyers who need to know how to shortlist grades and avoid a finish-failure, the gate sequence is BHmax → Hcj temperature suffix → coating class → machining class.
SmCo: thermal headroom and corrosion resistance, with cobalt price exposure
SmCo 2:17 (REC-26 to REC-32 class) gives 24-32 MGOe with a Curie temperature of 720-840 °C and intrinsic coercivity in the 15-25 kOe range, which is why aerospace, downhole and turbo-machinery applications route to it when the operating envelope goes past 200 °C or the atmosphere is wet [S1][S3].
The 1:5 variant (REC-16 to REC-22) trades energy density for a higher Hcj ceiling and is more machinable, but its (BH)max tops out near 22 MGOe. Buyers should expect roughly 3-5x the NdFeB unit price because of Sm and Co raw-material exposure, plus tighter tolerances: sintered SmCo is brittle, cannot be drilled or tapped with conventional tooling, and is usually supplied as OD/ID ground or wire-EDM-finished pieces.
AlNiCo: temperature-stable, mechanically tough, lower energy density
Cast AlNiCo 5/8/9 grades deliver 4-9 MGOe with a Curie temperature near 800-860 °C and a reversible temperature coefficient of -0.02 to -0.03 %/°C on Br, which is the lowest of the four families and the reason it is still specified for meters, sensors and high-temperature holding fixtures. Sintered AlNiCo trims (BH)max slightly but improves tolerance to ±0.05 mm and is the right pick for small precision components where machining is impractical. [S1]
Mechanically AlNiCo is the toughest of the four: it can be drilled, milled and ground with carbide tooling without the chipping and cracking risk that comes with sintered NdFeB and SmCo. Where buyers need to weigh magnetic path geometry against sensor IC compatibility, the relevant gates become temperature coefficient first, then mechanical machinability, then (BH)max.
Hard ferrite and soft magnetic composites: cost-down and AC-path families
Strontium- and barium-ferrite (SrO·6Fe2O3 / BaO·6Fe2O3) grades sit in a 1-5 MGOe (BH)max window with Br of 0.2-0.45 T and Hcj of 1.6-3.5 kOe; they are roughly 5-10x cheaper per kg than NdFeB, electrically non-conductive, corrosion-proof, and dominate DC motor arc segments, refrigerator magnets and loudspeaker rings. Curie temperature is around 450 °C, so thermal headroom is sufficient for most motor environments [S1].
For AC flux paths — stator laminations, chokes, transformer cores, solenoid yokes — soft-magnetic families take over: non-oriented Si-steel (1-3.5 wt% Si, 50-130 W/kg core loss at 1.5 T / 50 Hz), grain-oriented Si-steel (3 % Si, 0.3 mm or 0.23 mm gauge, used in power transformers), Fe-Si-Al sendust (6-9 % Al, lower losses at high frequency), Fe-Ni permalloy / mumetal (30-80 % Ni, μi of 20,000-100,000 in 0.1 mm tape) and soft-magnetic composites (sintered Fe powder with dielectric coating, 3D-flux capable, eddy-current-limited at high f). Lamination gauge is the dominant loss lever: 0.23 mm lamination cuts core loss 15-25 % vs 0.35 mm at 50 Hz, with the trade of higher stacking labour and lower stacking factor (0.93-0.95 vs 0.95-0.97).
Selection criteria stack: BHmax, Hcj, Tmax, corrosion, tolerance, cost
Use a six-gate stack to compare the four permanent-magnet families: [S2]
Gate 1 (BH)max — sintered NdFeB 33-53 MGOe, bonded NdFeB 6-12 MGOe, SmCo 2:17 24-32 MGOe, AlNiCo 4-9 MGOe, hard ferrite 1-5 MGOe. Gate 2 intrinsic coercivity (Hcj) — NdFeB N-grade 11-12 kOe, UH/AH/VH 25-30 kOe, SmCo 15-25 kOe, AlNiCo 0.6-1.6 kOe, ferrite 1.6-3.5 kOe. Gate 3 max operating temperature — NdFeB 80-230 °C depending on suffix, SmCo 250-350 °C continuous, AlNiCo 450-550 °C, ferrite 250 °C.
Gate 4 corrosion class — ferrite inert, AlNiCo inert, SmCo moderate (still takes a coating on chloride exposure), NdFeB reactive (Ni-Cu-Ni or e-coat baseline). Gate 5 tolerance and machinability — AlNiCo and ferritic Si-steel machine on conventional carbide, sintered rare-earths are ground or wire-EDM only; bonded NdFeB and SMC can be pressed to net shape and skip secondary machining. Gate 6 cost per kg of energy product — hard ferrite sits lowest, NdFeB highest; the crossover where SmCo becomes more cost-effective is generally above 180-200 °C or in tight-tolerance sub-5 g pieces where scrap rate on NdFeB dominates. For buyers mapping this stack against linear and crossed-roller motion components that share a machine, the same lot-level traceability and PPAP-style documentation should travel with the magnet PO.
Application map: which family goes into which 2026 build
EV traction motors, industrial servo spindles, robot-joint actuators and wind-generator PMSG rotors route to sintered NdFeB in the 38-52 MGOe range with a SH/EH/AH suffix for continuous operation above 150 °C, typically with Ni-Cu-Ni plus e-coat for humidity robustness. Aerospace actuators, downhole MWD/LWD tools, turbo-machinery speed sensors and military-spec solenoids route to SmCo 2:17 where the continuous-use ceiling sits above 250 °C or the atmosphere is wet/hot. [S3]
Instrumentation meters, Hall-sensor bias magnets, reed-switch carriers, motor tachometer rings, and high-temperature fixtures route to cast or sintered AlNiCo 5/8 because of the -0.02 %/°C coefficient. White goods, fractional-HP DC motors, speaker rings, separator/ferrite-rod applications route to SrO ferrite. Transformer cores, distribution and traction stator/rotor laminations, high-frequency chokes and CMC inductors route to Si-steel, sendust, permalloy/mumetal or SMC depending on frequency, flux density and form-factor. The 2026 laboratory R&D track — Co- and Fe-based ferromagnetic microwires tuned by field and stress — adds an in-situ waveguide tuning route for sensor and RF work [S2].
Limits, failure modes and verification levers
Failure modes are family-specific: NdFeB loses 30-50 % of Br at 200 °C unless the SH/AH/VH suffix is specified, and uncoated NdFeB swells and fractures in chloride-bearing humidity within 6-12 months; SmCo 2:17 cracks on aggressive mechanical impact and cannot be conventionally drilled; AlNiCo is magnetically "soft" in the sense that a small reverse field reorients magnetization, so it should not be specified for dynamic air-gap environments; hard ferrite saturates early and limits peak flux density; Si-steel laminations fail at high frequency (above ~400-500 Hz for 0.35 mm gauge) unless down-gauged to 0.1-0.2 mm or replaced with sendust / amorphous / nanocrystalline ribbon. [S1]
Verification levers: request IEC 60404-8-1 / 60404-8-5 grade certificates for hard ferrite and NdFeB; require ASTM A753 / IEC 60404-8-6 for permalloy; ask for Hcj-vs-temperature curves (not just room-temperature Br and Hcj), salt-spray test data (ASTM B117, 48-96 h) for NdFeB coating, dimensional report (CMM for ±0.02 mm features), and Dy / Tb / Co / Sm lot-level ICP-OES assay so you can audit rare-earth content against the cert. Trackable 2026 signals to watch: Dy / Tb spot price moves (NdFeB heat-stability cost driver), Sm / Co allocation policies on defence contracts, and Si-steel strip lamination gauge down-trends as more EV traction motors move from 0.35 mm to 0.25 / 0.20 mm to chase core-loss reduction.
For related coverage, see SCADA Software 2026 Price & Cost Guide: License, Tag and Sourcing Levers.