Internal magnetic structure of dextran coated magnetite nanoparticles in solution using small angle neutron scattering with polarization analysis

For many applications, the internal magnetic domain structure of magnetic nanoparticles may play a critical role in the determination of their collective magnetic properties. Here we utilize polarization analyzed small angle neutron scattering (PASANS) to study the individual magnetic morphologies of an interacting aqueous Fe₃O₄ nanoparticle system. Our results demonstrate that the total magnetic moment of the colloid is randomized, as expected in low fields, while the nuclear structure is anisotropic. Model fits indicate that the magnetic domains within the nanoparticle core at 1.5 mT have dimensions that approximate those of the structural grains perpendicular to the field, but the domains extend over multiple grains along the field direction. The asymmetry in the magnetic domain formation in weak fields undoubtedly contributes to the magnetic anisotropy and thus to the enhanced heating reported for hyperthermia applications of these systems.