Definition
A material that is weakly repelled by a magnetic field and cannot be magnetized. When placed near a magnet, a diamagnetic material produces a very small magnetic force in the opposite direction to the applied field. Common examples include copper, gold, bismuth, and water.
Plain English
A material that pushes back slightly against a magnet instead of being pulled toward it, and that cannot itself be turned into a magnet.
Context Anchor
Seen in basic electricity, magnetism, and aircraft instrument discussions, especially when explaining how different materials behave near magnetic instruments.
Derivation
From the Greek 'dia-' meaning 'across' or 'through,' and 'magnetic.' The idea is that the magnetic effect passes through the material in a way that opposes the field, rather than aligning with it. Knowing 'dia-' means 'across' helps explain why these materials work against the field instead of with it.
Why Pilots Care
Materials near a magnetic compass must be chosen carefully. Diamagnetic and other non-magnetic materials are used in compass housings, instrument panels, and nearby fittings so they do not pull the compass off its true reading.
Analogy
Think of a magnet trying to pull on different objects. A diamagnetic material is like an object that gives the magnet a tiny push back instead of moving toward it.
Intuition Check
Do not read “diamagnetic” as simply “not magnetic.” It means the material has a very weak magnetic reaction in the opposite direction.
Example Sentence 1
Copper is a diamagnetic material, which is one reason it is safe to use in fittings close to the magnetic compass.
Example Sentence 2
The repair manual warned against using certain diamagnetic materials near the magnetic sensors in the attitude heading reference system.