Magnetic properties of shape anisotropic nanoparticles
Data storage applications require a maintained magnetisation state. Magnetic imaging and the experimental cancer treatment magnetic hyperthermia rely on electromagnetically-induced relaxation. Given that understanding magnetisation and relaxation in nanomaterials is critical to developing innovative applications, the EU-funded project JANUS DYNAMICS characterized them quantitatively. Next to shape anisotropic nanoparticles, scientists chose the novel configuration of colloidal Janus particles (named after the two-faced Roman god Janus) that consists of two hemispheres with different physical or chemical properties. The asymmetric nature of such particles makes them an appropriate model system for studying magnetisation relaxation effects. These are dependent on the interplay between magnetic anisotropy and volume, properties in turn influenced by nanoparticle composition, shape, interface effects and inter-particle interactions. Researchers employed advanced time-resolved X-ray and neutron scattering techniques to study static magnetisation and time-dependent magnetisation relaxation. The team focused on several cutting-edge topics in the field of magnetic materials including exchange bias and Néel relaxation. Exchange bias is related to giant magnetoresistance. It is critical to magnetic recording and important in many advanced electronics including computers and MP3 players. Néel relaxation is a phenomenon of superparamagnetism where magnetisation of ferromagnetic nanoparticles can randomly flip direction under the influence of temperature. Janus particles are quickly gaining interest due to the broad potential for applications associated with their varied shapes and components. Characterisation of magnetisation and relaxation behaviours of these anisotropic nanoparticles will thus be important to the development of novel technological applications exploiting them.
Keywords
Magnetisation, relaxation, anisotropic, Janus particles, magnetic anisotropy, exchange bias, Néel relaxation, nanoparticles
