Definition
A ferromagnetic material that becomes strongly magnetized when placed in a magnetic field but loses most of its magnetism as soon as the field is removed. Soft magnetic materials, such as soft iron and silicon steel, have low magnetic retentivity and are used in transformer cores, relays, generator pole pieces, and electromagnets where the magnetism must turn on and off quickly with the applied current.
Plain English
A type of metal that becomes a magnet only while an electric or magnetic field is acting on it, then stops being magnetic almost immediately when that field is taken away.
Context Anchor
Seen in aircraft electrical and instrument-system discussions, especially around relays, solenoids, transformers, generators, and magnetic compass parts.
Derivation
The word 'soft' here is borrowed from metallurgy, where it described iron that was physically easy to work. Early electrical engineers noticed that this same easily-worked iron also let magnetism come and go easily, so the term carried over to describe magnetic behavior. It does not refer to physical softness in this context.
Why Pilots Care
Placing these materials too close to a magnetic compass can create temporary deviation that disappears when the influence is removed, requiring careful component siting during installation and maintenance.
Analogy
A small iron paper clip near a magnet acts like a magnet while the magnet is close, but it usually loses most of that effect after the magnet is taken away. That is the basic idea of soft magnetic behavior.
Intuition Check
Soft does not mean bendable, weak, or rubbery here. It means easy to magnetize and easy to demagnetize.
Example Sentence 1
The core of a relay is made from a soft magnetic material so the relay releases the moment current to the coil is cut.
Example Sentence 2
Certain avionics transformers rely on soft magnetic material because it responds efficiently to changing electrical currents without holding residual magnetism.