Date of this Version
PRL 95, 237209 (2005)
Magnetizations and magnetic moments of free cobalt clusters CoN (12< N <200) in a cryogenic (25 K ≤ T ≤ 100 K) molecular beam were determined from Stern-Gerlach deflections. All clusters preferentially deflect in the direction of the increasing field and the average magnetization resembles the Langevin function for all cluster sizes even at low temperatures. We demonstrate in the avoided crossing model that the average magnetization may result from adiabatic processes of rotating and vibrating clusters in the magnetic field and that spin relaxation is not involved. This resolves a longstanding problem in the interpretation of cluster beam deflection experiments with implications for nanomagnetic systems in general.