When the sample is removed from the external field the spins return to a random orientation. Another important distinction between compass needles and nuclear spins, is that spins possess angular momentum. Note that the Larmor frequency depends on the strength of the external magnetic field in which the spin finds itself. In other words, spins in different magnetic fields resonante at different Larmor frequencies. It is this property of NMR that can be used to localize spins in space for imaging or to determine what molecule they are a component of through spectroscopy.
Spins rotate around the direction of the external magnetic field.
This motion is reminiscent of a spinning top that has been tapped or is slowing down. The frequency at which a spin precesses is called the Larmor frequency and is proportional to the field in which a spin finds itself.