Endohedral clusters, formed by incorporating it single Mn atom into a cage of tin atoms, have been generated in the gas phase. Mass spectrometry reveals that a cage size of 10 tin atoms is necessary for the efficient incorporation of one Mn atom. Some of the cluster compounds with one Mn atom attached to the tin Clusters display large intensities compared to the pure tin clusters, indicating that the compound clusters are particularly stable. The manganese-doped tin cluster assemblies Mn@Sn-12, Mn@Sn-13, and Mn@Sn-15 have been further analyzed within a molecular beam magnetic deflection experiment. Interestingly, although the effect of the magnetic field on the behavior of Mn@Sn-12 is quite different from that of Mn@Sn-13 and Mn@Sn-15, the magnetic dipole moments are the same within the uncertainty of the measurements. Magnetic dipole moments have been found in close agreement with the spin quantum number S = 5/2 predicted by theory for Mn@Sn-12, indicating that the magnetic moment of the Mn atom is not quenched. This supports the idea that within a tin cluster cage a single Mn atom can be encapsulated, resulting in the formation of endohedral clusters consisting of a central Mn2+ ion Surrounded by a particularly stable Zintl-ion cage Sn-N(2-). The observed molecular beam profiles indicate that at a nozzle temperature of 55 K the magnetic moment is strongly locked to the molecular framework of Mn@Sn-12; in contrast, the magnetic moment of Mn@Sn-13 and Mn@Sn-15 tends to align with the magnetic field. The experiments therefore demonstrate that the size of a presumably nonmagnetic cluster cage might have a fundamental influence on the magnetization dynamics of paramagnetic species. The influence of vibrational excitation on the Stern-Gerlach profile of Mn@Sn-12 IS further analyzed, and it is shown that the behavior of Mn@Sn-12 at elevated nozzle temperatures changes continuously toward a nonlocked moment, pointing to size- and temperature-dependent magnetization dynamics.