Making Bar Magnets: Heating & B Field Placement

[cragar]

If I wanted to make bar magnets would I heat up the metal and then place it in a B field of a solenoid and then cool it down in the field to keep the magnetization? It seems if i heated it up first the atoms would be more easily aligned in the B field, And then cool it down to preserve this state.

 

[xts]

That's not quite such that atoms get lose, but, of course, if you cool the ferromagnetic in presence of external field, the magnetisation stays. Just keep in mind that for iron the critical temperature (called Curie's temp - wiki on it and on ferromagnetism!) is about 1000K.

You may just put iron in sufficiently strong magnetic field even at low temperature to keep it magnetised.

You should also know that even small changes in proportion of steel components (and even its physical trechnological treatment) have dramatic influence on its magnetic properties. Some kinds of steel cannot be magnetised at all (e.g. the steel used for cores of transformers).

 

[cragar]

So what would be the best way to make a magnet. What temp should I have it when I place it in the B field.

 

[xts]

So what would be the best way to make a magnet. What temp should I have it when I place it in the B field.

Just a room temperature - place your iron bar in stron magnetic field (inside solenoid).
You must play with different kinds of steel - it is pretty unpredictable. Two nails looking the same may have pretty different magnetic properties. Rule of thumb is that soft low carbon steel is easier to magnetize than springy, hard one.

 

[regon]

im also trying to make a permanent magnet. so i have a couple of questions.
when magnetised how do you know which is the north and which is the south poles?
can you make a magnet with only one pole? north or south?
and what can dampen or insulate metals from being attracted by the magnet?

 

[xts]

how do you know which is the north and which is the south poles?

The Earth would tell you. Suspend your magnet on a thread. North pole tends to point towards North and south pole tends to point toward South.

can you make a magnet with only one pole? north or south?

No one ever succeed. Wiki on magnetic monopole.

and what can dampen or insulate metals from being attracted by the magnet?

Try it at home!
Put a nail into a plastic bottle and see if it is attracted by magnet.
Put it into carton box, and try again.
Put it in an alu-can and try again.
Put into steel can and try...

 

[regon]

thanks xts . one more question
electro magnets, how do can you tell north or south? for a solenoid electromagnet to be exact.

 

[xts]

electro magnets, how do can you tell north or south?

The Earth would tell you. Suspend your electromagnet on a [STRIKE]thread[/STRIKE] wires. North pole tends to point towards North and south pole tends to point toward South.

 

[henlus]

Another way to know the poles of an electromagnet is to use the direction of current flow. At the north end, current flows in anticlockwise direction while at the south end, current flows in clockwise direction.

 

[Gordianus]

I've always checked magnets with a cheap compass. Far simpler than suspending the magnet from threads/wires.