Thermosensitivity Through Exchange Coupling in Ferrimagnetic/Antiferromagnetic Nanocrystalline Composites for Spatially Resolved Thermometry

Temperature is a fundamental physical quantity critical to every scientific discipline. Noncontact measurement of temperature beyond the surface of a given 3D volume is generally not possible; however, a temperature-sensitive variant of magnetic particle imaging (MPI) hopes to remedy this metrological deficiency. In order to enable thermal magnetic imaging for near room temperature applications (200 K to 400 K), it is necessary to develop magnetic materials that exhibit a strong temperature dependent magnetization (thermosensitivity) in this range. We demonstrate that nanocrystalline composites of ferrimagnetic iron oxide embedded in antiferromagnetic CoO and Ni doped CoO produce a sharp change in magnetization with temperature; with one possibility being that this is due to the Néel temperature of the antiferromagnets. The nanocrystalline composites were synthesized by a seed mediated colloidal synthesis approach, and the structure and morphology were characterized by XRD, TEM, and STEM. Temperature dependent magnetization has been measured by DC liquid and powder magnetometry.