Soft magnetic MIM grades come in three practical families: Fe-50%Ni for high permeability and low coercivity, Fe-3%Si for low core loss and higher electrical resistivity, and cost-oriented Fe-2%Ni; published supplier examples run from roughly 3,300 to 30,000 permeability and 0.17 to 1.5 kA/m coercivity — treat every number as a typical band, not a constant.
This page compares the magnetic MIM families on the figures of merit engineers actually specify — maximum permeability, coercive force, saturation flux density and sintered density — and states where each one wins. For the full material family overview see the MIM materials guide; for a single deep alloy page see Fe-Ni 36 alloy characteristics.
What Soft Magnetic MIM Grades Exist
Metal injection molding serves the same soft magnetic alloy families that relay and sensor makers use conventionally: Fe-50%Ni (a high-nickel permalloy-type grade), Fe-3%Si (an electrical-iron type), and lower-nickel Fe-2%Ni / iron-based grades positioned on cost. Emitech’s material list includes soft-magnetic Fe-Ni alloys among its MIM families, aimed at solenoid components, pole pieces, sensor cores and magnetic structures.
What MIM adds over conventional press-and-sinter powder routes is density: published soft magnetic MIM densities sit around 7.5–8.0 g/cm³, and suppliers consistently tie that density gain to better magnetic performance. Complex near-net shapes — cores with integral flux paths, armatures with molded details — come in the same operation, which is why magnetic parts are one of the quieter MIM success stories.
Permeability, Coercivity and Density Compared
The table below collects published supplier example values. These are data-set-specific, not universal constants: composition, sintering cycle, heat treatment and test method all move the numbers. Compare grades within one supplier’s data set, and qualify actual values on real parts.
| Grade family | Typical permeability | Typical coercivity | Typical density | Positioning |
|---|---|---|---|---|
| Fe-50%Ni | ~30,000 (supplier example) | ~0.17 kA/m | 7.85–8.0 g/cm³ | High permeability, low coercive force |
| Fe-3%Si | ~6,700 (supplier example) | ~0.69 kA/m | ~7.55 g/cm³ | Low core loss, higher resistivity |
| Fe-2%Ni | ~3,300 (supplier example) | ~1.5 kA/m | ~7.75 g/cm³ | Cost-oriented soft magnetic iron |
One published bulk-alloy study illustrates the spread: Fe-Ni processed to 96% relative density reached coercivity as low as 20 A/m and full-field induction near 1.55 T, while Fe-Si reached about 32 A/m and 1.5 T — different processing, different test conditions, different answers. That is exactly why this page quotes bands.
Why Density and Interstitials Decide the Numbers
Magnetic response follows sintered density: pores interrupt domain walls the same way they cut load-bearing cross-section in structural parts. The density spread in the table — 7.55 g/cm³ for one Fe-3%Si grade versus up to 8.0 g/cm³ for Fe-50%Ni — is part of the performance story, and higher-temperature or longer sintering cycles that close porosity directly improve permeability and coercivity.
Interstitials are the other lever. Sources consistently emphasize that carbon, nitrogen and oxygen must sit at very low levels to preserve soft magnetic performance: carbon and nitrogen form precipitates that pin domains, and oxygen contaminates particle boundaries. A soft magnetic MIM program lives or dies on feedstock purity and a clean sintering atmosphere, which is why magnetic grades are quoted as a distinct material class rather than a side note.
Choosing by Application: Solenoids, Pole Pieces, Shielding
For solenoids, armatures, relays and switches, Fe-3%Si is the classic answer: moderate permeability, higher electrical resistivity for lower eddy-current loss, and low hysteresis loss in switching service. Where the design needs maximum permeability and the lowest magnetizing force — pole pieces, sensor cores, magnetic shielding, precision magnetic structures — Fe-50%Ni grades are positioned ahead despite higher cost, with published coercivity around 0.17 kA/m in one supplier data set.
When the magnetic requirement is modest and cost dominates, Fe-2%Ni-class grades at roughly 3,300 permeability and 1.5 kA/m coercivity do honest work. The selection logic is the same as any MIM decision: define the functional magnetic requirement first, then let the alloy and the density target follow — not the reverse. Emitech’s capabilities page lists the equipment behind these materials.
Heat Treatment and Testing Caveats
Soft magnetic MIM grades often need a post-sinter anneal to hit their published magnetic values — the sintered-then-cooled state is not automatically the optimized state, and suppliers describe magnetic performance against a specified heat-treat condition. Ask which condition a data sheet number refers to before comparing it with anything.
On testing: permeability is not one fixed value per alloy. Initial permeability, maximum permeability and DC versus AC excitation give different answers, and a headline number from one test method is not directly comparable with another supplier’s. When a program is serious, qualify magnetic performance on sintered sample parts in the actual magnetic circuit — the same discipline Emitech applies to material selection generally.
Frequently Asked Questions
Q: Which soft magnetic MIM alloy should I pick for a solenoid plunger?
Fe-3%Si is the classic solenoid, armature and relay choice: moderate permeability, higher electrical resistivity for lower eddy-current loss and low hysteresis loss in switching service. If the design needs maximum permeability and minimum magnetizing force, Fe-50%Ni grades are positioned ahead at higher cost. A DFM review against the actual magnetic circuit settles it.
Q: What permeability and coercivity can I expect from MIM Fe-50%Ni?
Published supplier examples show permeability on the order of 30,000 and coercivity around 0.17 kA/m for Fe-50%Ni, versus roughly 6,700 and 0.69 kA/m for Fe-3%Si. These are data-set-specific typical values, not constants — density, heat treatment and test method all move them.
Q: How much does sintered density affect magnetic performance in MIM?
Materially. Soft magnetic MIM densities run about 7.5–8.0 g/cm³, and suppliers consistently tie the density gain over press-and-sinter routes to better permeability and coercivity. Pores interrupt domain motion the same way they weaken structural cross-sections, so the sintering cycle is a magnetic decision, not just a mechanical one.
Q: Do soft magnetic MIM parts match wrought alloy magnetic performance?
Not automatically, and claims that they always do should be avoided. Published studies show processed Fe-Ni reaching coercivity as low as 20 A/m at 96% relative density, but values depend on interstitial content (C, N, O must be very low), heat treatment and test method. Qualify on sintered sample parts in the real magnetic circuit.
Q: Do MIM soft magnetic grades need heat treatment?
Often yes. The as-sintered condition is not automatically the optimized magnetic condition; suppliers quote magnetic performance against a specified post-sinter anneal. Always ask which condition a data sheet number refers to before comparing grades or suppliers.
If a solenoid, sensor core, pole piece or shielding component is on your drawing, send it through the contact page — Emitech answers quote requests within 24 hours, including magnetic grade and density-target recommendations.
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