Examining Relationships Between Synthesis, Structure and Magnetism in Nanomaterials with X-ray Spectroscopy
This talk details synchrotron x-ray investigations of two ferromagnetic materials that show unexpected magnetic properties on the nanoscale: cobalt carbide nanoparticles and epitaxial lanthanum cobaltite thin films. Cobalt carbide is not known to be a strong ferromagnet in the bulk phase, yet nanoparticles of this material synthesized by wet chemical methods have properties comparable to known rare-earth free permanent magnets. Lanthanum cobaltite is a paramagnetic material that becomes ferromagnetic when synthesized as a thin film. To gain insight into the unique magnetic properties of these materials, a variety of x-ray spectroscopy based experiments were carried out. In lanthanum cobaltite, the effects of epitaxial strain on the atomic and electronic structures of the material were measured using x-ray absorption fine structure (XAFS) spectroscopy and x-ray diffraction. From the observed atomic and electronic structures, the nature of the strain induced magnetic phase is deduced. A combination of x-ray magnetic circular dichroism (XMCD) spectroscopy and time resolved quick XAFS spectroscopy was used examine the relationship between the Co-carbide nanoparticle synthesis and the resultant magnetic properties. These results give insight into how to tailor the synthesis of nanomaterials to optimize magnetic properties.