If you "condition" the AlNiCo magnet, that might help keep it a little more stabilized. Conditioning is magnetizing the magnet to saturation and then demagnetizing it by 5-15% or whatever you need. I am not sure if this will work in your situation
If you need more magnetic field, you can switch to RareEarth magnets instead of Ferrites. They are 3-4 times stronger than Ferritte magnets. For samples, contact companies like Dexter Magnetics or Magnet Sales.
To measure magnets, www.magsys.de. They have inexpensive handheld gaussmeter.
