Molecular Beam Studies of the Magnetic Moments of Small Metal Particles
This dissertation is a report of the study of small metal particles in a molecular beam using a quadrupole separating magnet. The particles were formed by evaporation in a low pressure, low temperature, helium atmosphere. The in vacuo molecular beam was formed using a differential pumping technique. A time-of-flight mass spectrometer was employed to monitor cluster populations. A 12 kilogauss pole tip field, permanent quadrupole magnet was used to search for variations in the magnetic susceptibilities of species with an even versus an odd number of atoms. The primary material of study was bismuth with between 3 and 19 atoms per particle. No effect was observed in any cluster size. When the performance was checked with vacuum evaporations of bismuth clusters one through four; an effect from the magnet was only observed in the monomer. These results are discussed in relation to a computer simulation of the system. The trajectories of particles from a Monte Carlo Source were integrated through the magnet with a Runge Kutta Algorithom. The calculations show that fragmentation of the clusters during the electron impact ionization process (beam energy 45V) was significant. Fragmentation of the dimer to the monomer was derived from the program results. Assuming a one Bohr magneton minimum magnetic moment for the trimer, the results show all of the observed trimer was due to fragmentation. The dissociation of the dimer into the atomic species explains the small effects observed on the atomic particles. In addition to bismuth, some vacuum evaporation work on indium monomers and antimony one through four are also reported. Together with the experimental details of the program is presented a brief review of the theoretical and experimental developments of the field as well as a discussion of the various theoretical inputs required for predictions of the interaction of these particles with an external magnetic field. The behaviour of the source is briefly discussed in terms of elementary nucleation theory. A novel method for measuring the magnetic field strength inside the small aperture quadrupole (3mm) employing a single turn search coil integrator is described. Finally some thoughts on future work are presented.
- Pub Date:
- December 1985
- Physics: General