TABLE OF CONTENTS Since the clusters in a molecular beam are free from any interation with a matrix, it becomes possible to determine their intrinsic magnetic properties. The dependence of the magnetic properties on the cluster size can be determined in a Stern-Gerlach experiment, in which the clusters interact with an applied inhomogeneous magnetic field and are deflected from the original trajectory. The deflection of a cluster traveling with a velocity v transversally to the field gradient direction (defined as the z direction) is given by [1, 2]
| (9.1) |  |
where m is the cluster mass, ?B/ ?z is the magnetic field gradient and K is a constant which depends on the geometry of the apparatus. This equation indicates that the deflection is proportional to the cluster magnetization M( B). The experiments [1 8] are normally analyzed assuming that the ferromagnetic clusters are single-domain particles following the super paramagnetic behavior [9], which is true under conditions such that the thermal relaxation time is much lower than the time required by the clusters to pass through the poles of the Stern-Gerlach magnet [10]. In that case the atomic moments of a particle with N atoms are coupled by the exchange interaction, giving rise to a total magnetic moment ? N that is free of the cluster lattice. This orientational freedom allows the magnetic moment to align with an external magnetic field. For an ensemble of particles in thermodynamic equilibrium in...
