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.

Urve Kangro has written:

'Divergence boundary conditions for vector helmholtz equations with divergence constraints' -- subject(s): Boundary conditions, Helmholtz equations, Coercivity, Boundary value problems, Divergence