MuMvalues describe: Mu-metal
Big science (accelerators, light sources, public fusion)Quantum hardware
Why it wins
Extreme permeability soaks up stray field around beamlines, photomultipliers, and qubit cryostats where compensation coils cannot.
Why not the alternative
Ordinary iron saturates and remembers; active coils fight AC but not DC gradients well.
Watch out
Permeability dies if machined or shocked after the final hydrogen anneal.
Properties
The values below are candidate: compiled from the sources named, not yet individually validated.
Provisional provenance: ASM Handbook: properties, corrosion, heat treatment; CERN Accelerator School, vacuum and materials proceedings.
Wet cleaning
| Recipe | degrease and DI rinse before the final anneal, then handle only by the edges |
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| Forbidden | any mechanical work after annealing: bending, drilling, dropping |
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| Limit | the anneal, not the wash: cleaning happens before it and never after |
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Vacuum and outgassing
| Outgassing, unbaked (10 h) | 3e-9 mbar·L/s/cm² |
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| Outgassing, baked | 2e-11 mbar·L/s/cm² |
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| Vapour pressure | negligible |
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Temperature
| Bake, assembled | 200 °C |
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| Vacuum degas | 1100 °C |
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| Braze / H2 firing | 1150 °C |
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| Metallurgical limit | anneal 1100–1175 °C in H₂: and the anneal is last |
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Thermal
| CTE | 12.7 ppm/K |
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| Thermal conductivity | 35 W/m·K |
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| Specific heat | 460 J/kg·K |
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| Emissivity | 0.2 |
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| Melting / softening | 1425 °C |
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Mechanical
| Strength | 160 ys MPa |
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| Tensile | 480 MPa |
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| Elongation | 40 % |
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| Young's modulus | 210 GPa |
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| Hardness | 120 HV |
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| Density | 8.75 g/cm3 |
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Electrical and magnetic
| Relative permeability | 20 000–100 000 initial; Cryoperm keeps it at 4 K |
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| Resistivity | 60 µΩ·cm |
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Engineering
| Corrosion | moderate |
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| Joining | formed first, annealed last |
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| Process notes | a hot bakeout de-anneals it, so the shield caps the system bake |
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| Availability and cost | shield makers, to drawing |
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Grades
| Mu-metal (80Ni) | room temperature shields, final hydrogen anneal after forming |
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| Cryoperm 10 | annealed for permeability at 4 K: cryostat shields |
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Sources · 1
- Compact ion-trap demonstrator, magnetic hygiene
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