This is my recommendation to repairing neodymium magnets that have been broken.
Strong magnets break very easily - ever atom inside a magnet wants to pull away from each other. So when a magnet breaks in half, the two parts do not want to go back together. Magnets are possible to fix with a little effort following my simple instructions.
Things you will need:
-A good magnet the same size
-Clamps (Irwin recommended)
-Tinfoil or aluminum foil
First, cover a good magnet in foil. Place the two broken parts of the broken magnet on top of it of the good one, the magnet pieces should stay on the good magnet, but most likely will not touch each other. Mix up some JB weld - JB weld is a very strong epoxy and that easily available at most hardware stores. JB weld is magnetic (not be confused with magnetized), this is best for this application by allowing flux to flow better thru the epoxy, however, it makes it a little more challenging to apply. Apply enough to coat the broken edge completely. Then use the clamp to push the magnet back together, being careful not to tear the foil. You may want to leave or remove the excess epoxy.
Some times you might need to be creative depending on how the magnet broke. This one had only a small corner broken off it, not enough area to hold on to the good magnet, first I applied the JB Weld and then with three clamps I was able to line it up right.
Allow to cure for 24 hours. After cured, carefully remove and remove the foil . Your magnet is almost as good as new, however, I would still recommend being careful with it, just in case.