The form of the Zeeman energy implies that the spins align with the direction of the effective magnetic field. What would happen, however, if the effective field would be allowed to point at any direction in space with no restrictions whatsoever?
The answer is very clear: the spins would then be allowed as well to orient at any given direction. This means that in such conditions, the spins can undergo significant changes in their orientation allowing to sense their motion easily. This is the principle behind our work presented in [PRL 116, 047204].
Later, we used this principle to sense the torques that originate from spin polarized currents that were injected using the spin Hall effect [Phys. Rev. B 95, 064401].
The ultra-high sensitivity of this method allows to measure the spin Hall effect in samples that are only two atoms thick.
Enhanced sensitivity for measurement of spins. Measurement concept and large angle nonlinear magnetisation response.