How to separate magnet from shaft?

[littlegiant]

I have this KB45 motor but I kinda screwed up the output shaft a little after grinding it down from 6 to 5mm diameter. The output shaft is sort of tapered now so pinions move around abit.

I intend to make a new motor shaft but how do I remove the magnet from the shaft? I've tried using acetone, freezing and hammering, twisting but they don't seem to work.

I wouldn't want to try using heat for fear of demagnetizing the rotor magnet.

Anyone has any good idea to go about doing this correctly?