Question

Which of the following can be done to demagnetize a permanent magnet

Answer 1

cutting the magnet in half
heating the magnet past the Curie point
bending the magnet
freezing the magnet to absolute zero

Answer 2

Heating a magnet past its Curie point will destroy the long range ordering.
Contact through stroking one magnet with another in random fashion will demagnetize the magnet being stroked, in some cases; some materials have a very high coercive field and cannot be demagnetized with other permanent magnets.