[hamdani yusuf (OP)]

If we put two opposing magnetic poles facing each other, those magnets will be pushed apart by a magnetic force. But if an iron plate is inserted between them, the pushing magnetic force can be reduced or even reversed into a pulling force.
Is there a formula determining how thick the iron plate is required to neutralize the pushing magnetic force between the same magnetic poles?

[evan_au]

how thick the iron plate is required

If the iron plate is driven into magnetic saturation, it acts as if the iron plate is no longer there.
- The magnetic saturation level is strongly dependent on the exact iron alloy
- The field strength of the magnet will also affect the plate thickness

It is also probably affected by the field shape of the two magnets(?)
- I expect that two "horseshoe" magnets (2 poles close together) would need a thinner sheet than a pair of bar magnets (poles apart)

See: https://en.wikipedia.org/wiki/Saturation_(magnetic)

[hamdani yusuf (OP)]

- I expect that two "horseshoe" magnets (2 poles close together) would need a thinner sheet than a pair of bar magnets (poles apart)

What is the reason?

[hamdani yusuf (OP)]

I guess that it depends on the material's permeability.
https://en.wikipedia.org/wiki/Permeability_(electromagnetism)#Values_for_some_common_materials
It should also depends on the strength of magnetic field on the surface of the magnetic poles