Science hopeful
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Hi

Are all things that are magnetic classed as magnets?

I know that a ferromagnetic material eg) iron can be temporarily turned magnetic by the application of an external magnetic field, say from a bar magnet. But although it can be magnetized, can the iron itself be used as a magnet to attract say a piece of steel? If not why is this so?

Do all the domains have to be pointing in the same direction for something to be a full magnet? Im guessing so since if a bar magnet is chopped in half, it makes 2 magnets and this could only happen if the above was true. If say only 50% are pointing one way, would the material merely become magnetic?
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Hi there,

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uberteknik
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(Original post by Science hopeful)
Hi

Are all things that are magnetic classed as magnets?
Hello and welcome to TSR. Some good questions which deserve some thought:

There is a blurring between the strict scientific definition of the EM (electro magnetic) forces and the everyday use of the term magnet or more specifically permanent magnet.

By scientific definition, all atoms are magnetic but because in most materials, the atoms/domains are randomly oriented, no useful force for everyday purposes is noticed.

By everyday definition then, all things that are magnetic are not classed as permanent magnets because we don't notice any magnetic forces on the human scale.

(Original post by Science hopeful)
I know that a ferromagnetic material eg) iron can be temporarily turned magnetic by the application of an external magnetic field, say from a bar magnet. But although it can be magnetized, can the iron itself be used as a magnet to attract say a piece of steel? If not why is this so?
Yes, the iron can and is used as a magnet. The application of the external field will cause the magnetic domains of the iron to align with it. In the process, the now aligned domain magnetic fields all sum to produce a much larger composite magnetic field. This is called induced magnetism.

When the external field is removed, not all of the domains will return to their original random orientations but will stay aligned. This leaves a residual magnetic field and is called remanance. The iron is therefore now a weak permanent magnet.

Stronger permanent iron magnets are made by increasing the remanent magnetic field alignment. Plaing it in a very strong external magnetc field, striking the magnet to physically align the domains, heating the iron to make alignment more likely, powdering the material to create smaller domains more easily ceorced into alignment etc.

(Original post by Science hopeful)
Do all the domains have to be pointing in the same direction for something to be a full magnet? Im guessing so since if a bar magnet is chopped in half, it makes 2 magnets and this could only happen if the above was true. If say only 50% are pointing one way, would the material merely become magnetic?
No. Only some of them - enough for the aligned domain fields to become useful in everyday terms.

When the domains all point in the same direction, there is a summation of the magnetic force now all acting in the same direction such that the magnetic properties become noticeable on the human scale of things.

But as explained previously, not all domains need to be aligned for it to be uselful as a permanent magnet, but some of them definitely do. The more that do, the stronger the magnet.
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Science hopeful
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Thank you - glad to be aboard!

Ahhh I see thats much clearer now.... So all materials once magnetized by an external means retain magnetic properties after the current is stopped, its just about the degree of magnetic force they retain. In basic terms its not a black and white situation?
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uberteknik
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(Original post by Science hopeful)
... So all materials once magnetized by an external means retain magnetic properties after the current is stopped, its just about the degree of magnetic force they retain. In basic terms its not a black and white situation?
Yes, it's a tad more complex (a bit beyond the A-level syllabus for a complete description) and all to do with the order and number of electrons of any given atom and a property of electrons called spin.

In non-magnetic (bulk) materials, the molecular structure is random, and/or, electron spin properties cancel resulting in no bulk net-magnetic force.

In ferromagnetic materials, electrons are arranged such that there is a net bulk sum of magnetic force.

From the periodic table, you will notice that ferromagnetic materials are grouped around certain shell configurations which obey the correct conditions of electron spin for the summation to occur.

If you want to learn more have a look at:

http://www.doitpoms.ac.uk/tlplib/fer...y_magnetic.php

http://en.wikipedia.org/wiki/Magnet
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Pessimisterious
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(Original post by uberteknik)
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Top info, thanks! You've given me a great start for the next semester. I start studying all this properly in a few days.

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Science hopeful
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Excellent advice..... much appreciated!

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