| As green technology advances, the need for cheaper, stronger permanent magnets becomes more and more vital everyday. Electric motors, like those used in wind turbines and electric cars, rely heavily on Dy doped Nd 2Fe14B in order to achieve the required efficiencies to be successful, however both Nd and Dy are expensive rare-earth elements that the field is trying to move away from relying on. In order to approach this issue, many are trying to combine these powerful permanent magnets with cheaper and more abundant soft magnetic materials in order to create exchange-spring magnets. While exchange coupling behavior has been studied for several decades now, there are major issues with controlling the uniformity in the generated materials leading to a limited understanding of the properties of these assemblies.;In order to address both of these issues at the same time, we devised an approach to create a hard magnetic nanoparticle of fcc-FePt, which was then shelled with the soft magnet Co. In order to gain the desired control of the final core shell particles, a mix and round bottom and microwave heating was utilized, the synthetic details of which are laid out in Chapter 2. Chapter 3 lays out the results from applying a layer-by-layer shell of Co onto a constant 5 nm FePt particle. From this shelling, the transition from hard-exchange to exchange-spring to decoupling of the core shell system can be observed. The limit of these regions were found to be very small, with the hard-exchange regime only being in the case of shell sizes smaller than 1.4 nm and decoupling occurring in the materials with >2nm of Co shelled on. This limited range is due to cobalt's short range coupling, which can not support strong coupling beyond 3-4 layers of Co. |
