Mu-metal
A nickel-iron alloy for magnetic shielding
Typical values for the temper in the title
Mu-metal is an alloy with about 80% nickel and about 4–5% molybdenum. Its magnetic permeability is very high, so it "draws" weak magnetic fields into itself and away from the shielded area. Saturation is low (about 0.75–0.8 T, typical).
It is used for magnetic shielding of sensors, medical devices, tubes and sensitive measuring equipment, and for cores of transformers and sensors for weak signals. In strong fields it saturates, so an outer iron shield is combined.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Density ρ | 8.7 g/cm³ | |
| Magnetic saturation Bs | ≈0.75–0.8 T (typical) | |
| Machinability | 60% | relative rating in the site database |
Chemical composition (wt %)
| Element | Range | Role |
|---|---|---|
| Ni nickel | about 80 (nominal) | high permeability |
| Mo molybdenum | about 4–5 | |
| Fe iron | balance |
Nominal composition (Carpenter HyMu 80). Standard: ASTM A753.
Conditions and product forms
In soft magnetic materials the magnetic properties are set by the final anneal. Any machining, bending or impact after the anneal lowers permeability and increases losses.
| Condition | Properties | When to choose it |
|---|---|---|
| Worked (before anneal) | low permeability | forming |
| Hydrogen annealed | maximum permeability | the finished shield |
Applications
- Magnetic shielding for sensors
- Shielding for medical devices
- Signal transformer cores
- Read heads
- Sensitive measuring equipment
Fabrication
Annealing
Required after any forming: in dry hydrogen at high temperature. Without annealing, permeability is far lower.
Handling after the anneal
Bending, welding, drilling or even impact lower permeability. Do all work before the anneal.
Strong fields
It saturates. In a strong field combine an outer layer of iron or 48% nickel.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| 48% Nickel-Iron (Permalloy 50) | — / | — | 48% nickel-iron: higher saturation · material page |
| Magnetic Pure Iron (Armco) | — / | Good | pure iron: for strong fields · material page |
| Invar 36 | 485 / 275 MPa | Good | Invar: nickel-iron for low expansion, not magnetics · material page |
Common mistakes
Bending or welding after the anneal
Permeability is destroyed. Re-anneal.
Using it alone in a strong field
It saturates.
Confusing it with Invar
Both are nickel-iron, but for different purposes.
Equivalents, standards and supply
| Standards | ASTM A753 |
|---|---|
| Forms | strip · sheet · formed parts |
| Producers | Carpenter (HyMu 80) · VAC · MuShield |
Learn more
Values are typical and for comparison only. For design, rely on the standard, the producer specification and the mill certificate. Sources: ASTM standards (B86, B386, B392/B393, B551, B708, B760 and others), producer data, and the METAL HUB materials database.
Updated: October 31, 2026