I did some research on line on how to de magnetize tools.
Some industrial procedures like grinding, sanding and polishing can make a piece of steel become magnetic. It seems that drill bits being subject to friction and spinning can also become magnetic with time.
I also read a post by a guy who had his garage hit by a lightning bolt, making every tool in there magnetic, and every nail holding the hardwood floor as well.
Some people said you can hit pieces of metal with a hammer to demagnetize it by misaligning the charges by the impact.
You can use a soldering gun to demagnetized small objects by passing it inside the loop in the tip while the gun is on, because the gun produces a strong alternating current that misalign the magnetic charges.
This guy made a homemade demagnetizer that works the same way: