[wilsong77 (OP)]

Hi,
Does anyone know whether a bar magnet would lose some of its magnetism if it is bent and broken into two?
Thanks,
Wilson

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[CliffordK]

If you break a magnet in two, you end up with two smaller magnets.

The strength of a magnet is related to its size.  So, the two smaller magnets will be weaker than the one original magnet.  However, the relationship may not be linear.  So a needle shaped magnet may be weaker than a coin shaped magnet of equal mass.

Thus, the sum of your two broken magnets may in fact be stronger than the original.

[evan_au]

Magnets can also lose some of their magnetism if the method of breaking them involves:
- Severe vibration (eg repeatedly hitting them with a hammer)
- Severe heat (eg cutting with a blowtorch)

[wilsong77 (OP)]

Thanks guys...
So, would breaking the magnet by bending it once, cause disruption to the alignment of some magnetic domains in the magnet? 

[CliffordK]

Probably not significantly.

I believe that most magnets are formed, then magnetized with a powerful electromagnet. 
The magnetic field required to magnetize (or demagnetize) the magnet is greater than the magnetic field within the magnet.

I'm not sure about the old U shaped magnets.

[wolfekeeper]

As CliffordK says breaking a bar magnet into two would probably increase the total effective magnetism, while reducing the maximum intensity.

Basically, the surface field strength of a magnet is only a function of its shape, not its size.

Disk magnets or rectangular magnets that are roughly the same height/width ratio give a very strong field for their mass.

Long thin magnets with poles at each end have a very intense magnetic field at each pole, more so than a short fat magnet, but only over a small area. They do have good reach though, you'll still have significant, although not terribly strong field at about one length, much further than a shorter magnet of the same diameter.

Disks are actually quite weak, they're too thin to give much field intensity; although they will often be reasonably strong around the rim where the ampere currents can be said to flow.

If you want really intense permanent magnets, forming them into Halbach arrays works very well, the world record is over 5 Tesla (that's more than many MRI machine that use superconducting magnets) but only over a very tiny volume indeed relative to the magnets.

I would guess that snapping a magnet could cause a measurable decrease in strength; but it would depend on the material; neodymium magnets probably not very much at all, may not be measurable, whereas ferrites it could be quite a lot. Samarium magnets would be hardly affected. AlNiCo magnets, you breath on them hard and they lose strength, all bets are off on those!

[CliffordK]

One thing I was thinking.

If you had two bar magnets:

[diagram=675_0]

Two bar magnets stuck together end to end would be essentially the same as one longer bar magnet.  Breaking them apart is easy...  depending on the strength of the magnet.

If you stick the two magnets together side by side, they will try to orient themselves in opposite polarities.  You will loose a little strength in this configuration.

You will get a slightly stronger strength if you orient them in the same polarity.

As wolfekeeper says, for a small area, the longer the magnet, the stronger the field through the face.  Thus, if you made a generator/motor out of say 1/2" long magnets, and one made out of the same number and diameter of 2" long magnets, the one with the longer magnets would be more powerful.

But, if you are testing the attraction to a larger piece of metal, then the more width in the magnet the better.

As wolfekeeper noted, the Halbach array essentially forces the entire strength of the magnet array in the same direction (of different poles).  It must be fixed in place.