Signature of multimers on magnetic susceptibility curves for mass-selected Co particles

Even if efforts are currently made to produce nanoparticle samples by deposition of preformed clusters with a size dispersion as low as possible, the incident particle size distribution is necessarily degraded because of the statistical formation of multimers. Here we study diluted Co cluster samples synthesized by mass-selected low energy cluster beam deposition. Transmission electron microscopy is used to determine the cluster size distribution and, in particular, the proportion of dimers. We then show how multimers can have a strong impact on magnetic measurements even if they constitute only a small proportion of the total particles. However, a thorough analysis can be used to determine the respective proportion of dimers and trimers just from the magnetization curves. These proportions are found to be in excellent agreement with the model of random cluster deposition. (C) 2011 American Institute of Physics. [doi:10.1063/1.3535554]