Definition
A high-permeability alloy of nickel and iron (typically around 78% nickel and 22% iron) that is easily magnetized by a weak magnetic field and demagnetized when the field is removed. It is used in aircraft instruments such as flux valves and magnetic compass components where sensitivity to small magnetic fields is required.
Plain English
A special metal mix of nickel and iron that responds very easily to magnetic fields. It picks up magnetism quickly when a field is present and lets it go just as quickly when the field is gone, which makes it useful inside instruments that need to sense the Earth's magnetic field.
Context Anchor
Seen in descriptions of aircraft compass systems, remote magnetic sensors, magnetic shielding, and some electrical instrument components.
Derivation
The name combines 'permeability' (a material's ability to support a magnetic field within itself) with 'alloy' (a metal mixture). Knowing this tells you exactly what the material is built for: high magnetic permeability.
Why Pilots Care
Its strong magnetic response helps reduce interference in cockpit instruments such as compasses.
Analogy
Permalloy is like an easy path for magnetism: a weak magnetic field can pass through it readily, instead of being resisted or scattered.
Intuition Check
Do not read “Permalloy” as “permanent magnet alloy.” Its key feature is not that it stays magnetized; it is that it responds to magnetic fields very easily.
Example Sentence 1
The flux valve uses a permalloy core to sense the direction of the Earth's magnetic field.
Example Sentence 2
The instrument used a Permalloy core to improve the accuracy of the magnetic sensing element.