Permalloy

Permalloy is a nickel–iron alloy known for its exceptionally high magnetic permeability and very low coercivity. It comprises a family of soft magnetic alloys with compositions around 80% nickel and 20% iron (commonly Ni80Fe20), though practical grades typically range about 75–85% nickel and 15–25% iron. The name reflects its use as a high-permeability material for magnetic circuits.

The alloys exhibit very low magnetostriction, which reduces mechanical noise and Barkhausen noise, yielding stable magnetic behavior. When properly heat treated, often including annealing in a mild magnetic field, permalloy attains high initial permeability and low coercive force, making it highly responsive to weak magnetic fields. Core losses are relatively low at power frequencies, though permeability generally decreases with increasing frequency and depth of modulation.

Applications of permalloy include soft magnetic cores for transformers and inductors, magnetic shielding for sensitive instruments, and the read/write gaps in magnetic data storage heads. It is also used in various sensors, such as fluxgate magnetometers and other devices that require high permeability with minimal hysteresis loss. The properties of permalloy can be tuned by heat treatment and minor alloying to balance permeability, saturation flux density, and loss characteristics for specific applications.

Processing and variants: The magnetic performance of permalloy depends on composition and thermal history. Manufacturers often cold-work and then anneal the material to optimize domain structure and permeability. Small adjustments in alloying and processing are used to tailor properties for particular soft-magnetic applications.