Although we cannot see magnetic field lines, we can detect them using iron filings. The tiny pieces of iron line up in a magnetic field.

Iron filings ... flow of iron filings. [BitBlt_Korry] calls his creation “「時場(じば)」”. Google translates this to “Jiba”, which means “magnetic field”.

In this situation they act as a magnet - but only whilst in the magnetic field ... soft. Iron is magnetically soft – it can be easily magnetised and demagnetised. Magnetic fields lines are ...

Magnetotactic bacteria synthesize magnetic iron nanominerals ... the bacteria to passively align with Earth's geomagnetic field lines in both the Northern and Southern Hemispheres.