Synthesis and Characterization of Novel Magnetic Nanodiscs for Magnetothermal and Magnetomechanical Transduction

Nanocomposites of soft magnetic ferrite and hard magnetic ferrite can enhance the versatility of magnetic nanomaterials as transducers for remote manipulation of cell functions, improving the magnetothermal and magnetomechanical transducing properties of the magnetic nanoparticles. To exploit these advantages, we introduce a novel class of magnetic composites: Fe₃O₄-CoFe₂O₄ core-shell nanodiscs. The exchange-spring coupling effect could be generated at the epitaxial interface between magnetite and cobalt ferrite, which is known to enhance the specific loss powers (SLPs, heating efficiencies in W/g_[Metal]).^[1] The increase in the ratio of the thickness to the diameter of the nanodisc due to the formation of the CoFe₂O₄ ensures the nanoparticles to position closer to the cortex region in the magnetic domain state phase diagram.^[2] The stronger tendency to be in a vortex ground state in the absence of a magnetic field is anticipated to yield greater torques exerted on targeted entities during the transition from a vortex to an in-plane magnetization state under an applied weak magnetic field. We investigate atomistic origins of these effects via high-resolution electron microscopy of individual particles and via scanning transmission electron microscopy (STEM) of the cross-sectioned nanoparticles. We additionally apply convergent beam electron diffraction (CBED) and analyses under Lorentz lens in STEM to investigate potential strain changes in these coupled ferrites under the magnetic field. We then connect our structural findings with functional measurements of thermal and mechanical transduction of magnetic field stimuli in the context of magnetic modulation of cell signaling.<br/>The characterization methods developed in this work pave way to analyses of multiple classes of particles with multiferroic properties that may find applications as versatile transducers of biological signaling.<br/><br/>[1] Lee et al. “Exchange-coupled magnetic nanoparticles for efficient heat induction”, Nature Nanotechnology, 6, 418–422 (2011)<br/>[2] Gregurec et al. “Magnetic Vortex Nanodiscs Enable Remote Magnetomechanical Neural Stimulation”, ACS Nano, 14, 7, 8036–8045 (2020)