It's not that the particles in a flex magnet sheet turn into a magnet, but rather that they are already magnetic and are aligned in a way that creates a magnetic field.

Here's the breakdown:

* Flex magnet sheets are made from a flexible polymer material mixed with magnetic particles, typically iron oxide (Fe3O4 or Fe2O3).

* These iron oxide particles are ferrimagnetic, meaning they have a permanent magnetic moment even without an external magnetic field.

* However, in their natural state, these particles are randomly oriented, resulting in no overall magnetic field.

* During manufacturing, the sheet is exposed to a strong magnetic field, which aligns the magnetic moments of the particles in the same direction.

* This alignment creates a net magnetic field, making the sheet itself a magnet.

Here's the key takeaway: The particles themselves are already magnetic, but it's the alignment of their magnetic moments that gives the sheet its overall magnetic property.