We describe the setup and the performance of a new pulsed Stern–Gerlach deflector and present results for small sodium-doped ammonia clusters Na(NH₃)_n (n = 1–4) in a molecular beam. NaNH₃ shows the expected deflection of a spin ½ system, while all lager clusters show much smaller deflections. Experimental deflection ratios are compared with the values calculated from molecular dynamics simulations. The comparison reveals that intracluster spin relaxation in NaNH₃ takes place on a time scale significantly longer than 200 μs. Assuming that intracluster relaxation is the cause of the reduced deflection, relaxation times seem to be on the order of 200 μs for all larger clusters Na(NH₃)_n (n = 2–4). Our work is a first attempt to understand the magnetic properties of isolated, weakly-bound clusters with relevance to the variety of diamagnetic and paramagnetic species expected in solvated electron systems.