Colloidal magnetic nanoparticles (MNPs) are an important class of nanomaterials that have found use in a host of applications such as biomedical imaging, remote sensing, drug delivery, and hyperthermia. Additionally, thermal imaging with temperature control is an emerging potential use for these versatile colloids. Applications usually exploit the very soft magnetic behavior found in certain materials, often ferrites, when they are confined in size to tens of nanometers in diameter or less. These nanomagnets produce a strong collective response to applied alternating (AC) magnetic fields while simultaneously remaining dispersed in media, such as a heterophasic liquid solvent. Their synthesis relies on reproducible, scalable, solution chemistry routes. Further, the size, shape, structure, and composition are tunable, which serve as levers to design and manipulate the magnetic behavior of these functional nanoscale materials.<br/><br/>Here we report on our efforts to develop colloidal MNPs with an improved response to applied AC magnetic fields, specifically for liquid-phase thermometry. A series of shape- and size-controlled MNPs based on ferrites were synthesized <i>via</i> solution routes and their AC magnetization response was determined as a function of temperature, frequency, and field amplitude using a high-precision, field-stabilized, magnetic particle spectrometer. Further, we exploit compositional doping of transition metals (Co, Zn) as a means of generating improved magnetization and thermosensitivity deriving from spin interaction within the MNPs. Detailed structural characterization, including electron microscopy, optical spectroscopy, and X-ray/electron diffraction, was performed to better understand the underlying factors influencing the magnetic response. In addition to extensive liquid- and solid-phase DC magnetometry studies, we have thoroughly interrogated the magnetic susceptibility of these particles under applied AC fields. We find the relaxation dynamics in solution, which dictate the AC response, are strongly influenced by the inherent magnetic and structural properties of the particles, as well as the local environment in which they are suspended. Collectively, these studies illuminate the complex behavior of MNPs under AC driving fields, reveal extensive correlations between nanoscale atomic structure and their magnetic response, and provide guidelines for the design of MNPs used in magnetic thermal imaging and other remote sensing applications.

Designing colloidal magnetic nanoparticles with strong liquid-phase AC field response for thermometry and other remote sensing applications

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.