High‐Moment Antiferromagnetic Nanoparticles with Tunable Magnetic Properties

Chemically synthesized superparamagnetic nanoparticles are widely used in biology and medicine for applications that include biomolecule purifications and cell separations, magnetic resonance imaging (MRI) contrast agents, and biomagnetic sensing. Magnetic nanoparticles with high moments are often desired to produce large signals for biomagnetic sensing or to avoid restrictive requirements for high magnetic field gradients in separations. Increasing the size of single-grain superparamagnetic particles is not a viable route because these particles become coercive and, consequently, spontaneously aggregate at sizes above the superparamagnetic limit (ca. 12 nm for Fe). One solution is to incorporate numerous magnetic nanoparticles into larger composites using matrices comprised of dextran or silica. However, there are still limitations associated with controlling the monodispersity, magnetic response, and variations in the number and size of the embedded nanoparticles. Here we report the fabrication of strongly magnetic, zeroremanence, monodisperse nanoparticles with tailorable mag-

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