ation of a single magnetic pole (north or south, but not
both) has not been done.
o
If a bar magnet is cut in half you get two new magnets.
o
If the cutting is repeated, more magnets are produced, each with a north
and a south pole.
o
Physicists have tried various ways to isolate a single magnetic pole
without success.
o
This is an active research field today since certain theories suggest they
should exist.

Microscopic examination reveals that a magnet is actually made up of tiny regions known
as domains
They are at most about 1mm in length or width.
Each domain behaves like a tiny magnet with a north and a south pole.
In an unmagnetized piece of iron, these domains are arranged randomly.
The magnetic effects of the domains cancel each other out, so this piece of iron is
not a magnet.


In a magnet, the domains are basically lined up in one direction.

A magnet can be made from an unmagnetised piece of iron by placing it in a strong
magnetic field.
In this case the domains may actually rotate slightly so they line up more to the
magnets field. More commonly, the borders of domains move so that the ones which already
line up with the magnetic field grow in size.

This explains how a magnet can pick up unmagnetised pieces of iron like paper clips.
The magnet's field causes a slight alignment of the domains in the unmagnetised
object.
The object becomes a temporary magnet with its north pole facing the south pole
of the permanent magnet.

An iron magnet can remain magnetized for a long time, and is referred to as a "permanent
magnet."
If you drop a magnet on the floor or strike it with a hammer, you may jar the
domains into randomness.
The magnet can lose some or all of its magnetism.
Heating a magnet can cause a loss of magnetism, since raising the temperature
increases the random thermal motion of the atoms which tends to randomize the
domains.
o
Above a certain temperature, known as the Curie temperature (1043 K for
iron), a magnet cannot be made at all.

But where are the domains coming from.
Even though a magnet might be at rest, the electrons in its atoms are in constant
motion.
The electrons basically move as though they are in little orbits around the
nucleus.
Soon we will be studying how a moving charge (current) creates its own
magnetic field.
More important, electrons spin on their own axis like tops, also making a
magnetic field.
Enough of these electrons moving the same way make a domain.