using force or threats to make someone do something

The material should have

high retentivity so that the magnet is strong and high coercivity

so that the magnetisation is not erased by stray magnetic fields

Materials with high coercivity and high retentivity.

the coercivity is test by drawing B-H curve.Coericivity is defined as without giving any magnitising force it will produce magnetic field intensity.

Soft magnets are easily magnetized and demagnetized, while hard magnets retain their magnetism once magnetized. Soft magnets have low coercivity and high permeability, making them suitable for applications like electromagnets. Hard magnets have high coercivity and are used in applications where a strong, lasting magnetic field is needed, such as in permanent magnets.