This is because the current kills the magnetized/domain
particles and so it becomes un-magnetized.
When the domains are magnetized they all face the direction of
the magnet but when they have been destroyed by an AC current...
they are pretty much jumbled together!
By heating the magnet,
By repeatedly stoking it with small hammer,
By winding the insulated copper wire around the magnet, like
electrical winders do and passing the electric current in right
direction to destroy magnetism in it.
An AC/DC voltage that flows through a coil with a steel bar
inside of it generates a powerful magnetism, depending on the
voltage applied, the number of spire, the section of the wire.
Transformers require AC to generate electromagnetic induction.
Take a strong magnet, and rub it across the weak one and it'll
make it stronger.
You can weaken or destroy an on objects magnetism with heat or
with physical shock such as banging it with something or on