Exploiting Spin Interaction in Magnetic Nanoparticles to Improve Magnetic Thermosensitivity and AC Field Response

Remote 3D magnetic thermometry is an emerging application of colloidal magnetic nanoparticles (MNPs). The technique employs MNPs to measure and image temperature remotely with high spatial resolution throughout a 3D volume. This metrology is based on the soft magnetic behavior found in many nanoscale ferrimagnets, which yields a strong and temperature-dependent collective response to applied AC magnetic fields. Here, we report MNPs specifically designed for remote 3D thermometry. A series of shape- and size-controlled colloidal MNPs based on ferrites were synthesized via solution routes and their AC magnetization response was determined as a function of temperature, frequency, and field amplitude. Further, we exploit compositional doping of transition metals and exchange coupling between core-shell heterostructures as means of generating improved magnetization and thermosensitivity from spin interaction within the MNPs. Extensive structural characterization was performed to better understand the underlying factors influencing the magnetic response, which revealed correlations between the nanoscale atomic structure of the particles and their magnetic performance. These studies constiute an important step in our effort to tune the response dynamics of MNPs under AC driving fields.