Some tricks while solving magnetism problems

Magnetic moment for any toroid is zero

When a magnetic dipole of moment M moves from a unstable equilibrium to stable equilibrium position in the magnetic field B, the kinetic energy will decrease by 2MB.

The intensity of magnetisation is produced in materials due to spin motion of electrons.

Magnetic moment of straight current carrying conductor is zero

Atoms that has paired electrons have the magnetic moment as zero

Magnetostriction - The length of an ironbar changes when it is magnetised.  When a iron bar is magnetised its length increases due to alignment of spins parallel to the field. This increase is in the direction of magnetisation. This effect is known as magnetostriction.