Spin particles not in a magnetic field

[denjay]

If spin particles are in $\vec{B} = 0$, then is it impossible to determine their magnetic moment at a given time given any investigative method?

 

[Vanadium 50]

I think you could use something like Aharonov-Bohm: create a region where B is 0 but A is not and interfere. Alternatively, you could accelerate these particles and measure their electric polarization (a moving magnetization becomes a polarization)