Any permanent magnet demagnetizes partially whenever it is taken out of a closed magnetic circuit.
If the magnet is made from a material with very high coercivity, the demagnetization may be negligible, but it is always recommended to store permanent magnets only with a piece of soft iron in contact with their N and S poles.
To reach the maximum remanence possible for a given material, a permanent magnet must always be magnetized after being assembled in the final magnetic circuit.
They are used in these applications, typically very high grade, unless you're buying a legacy product line.
In, say, a hybrid stepper the magnet is usually a wide thin round disc, sandwiched between two steel rotor lamination stacks. With the link below you can examine the BH curve and load line for a Ø20 mm N52 disc magnet, 2mm thick, at 20 degrees C. (It's not exact because this assumes a magnet in free space and neglects the steel of the rotor - but it's an illustration).
You'll notice that the load line (which assumes the magnet is in free air) is already landing within the "knee" where the intrinsic magnetization starts dropping rapidly. That's working too far along the hysteresis curve, where the poles are already starting to flip and demagnetize.
However, if that magnet were surrounded by the steel of the stator, the high permeability of the magnetic circuit would put the load line at a steeper angle, where the magnetic field through the magnet would be much higher. Small changes in permeability around that point would not damage the magnet, but allowing it to fall all the way down below the knee-point would. It would not be completely demagnetized by that, but it would lose some of its original strength.
If the magnet is made from a material with very high coercivity, the demagnetization may be negligible, but it is always recommended to store permanent magnets only with a piece of soft iron in contact with their N and S poles.
To reach the maximum remanence possible for a given material, a permanent magnet must always be magnetized after being assembled in the final magnetic circuit.