This book details three main studies. The first is an investigation of the effect of coating Fe nanoparticles in a gas to isolate the magnetic moments. An isolation or enhancement of the already increased magnetic moment of a Fe nanoparticle would have the potential for exploitation in high-moment materials. The other two investigations are of the behaviour of Fe nanoparticles in the rare earth matrices Ho and Dy. Transition metals and rare earth metals normally couple antiferromagnetically at their interface, however the intention of this work was to determine if this also happens when the Fe is incorporated as pre-formed clusters. The motivation for this is: if the interactions between the rare earth and the transition metal is switched to be ferromagnetic then the Curie temperature of the rare earth could be increased without a large decrease in its saturation magnetisation. Samples were grown using a gas aggregation source and measurements were made using vibrating sample magnetometry (VSM), X-ray magnetic circular dichroism (XMCD) and transmission electron microscopy (TEM).