Dynamics of paramagnetic nanostructured rods under rotating field

The dynamical rotational behavior of magnetic nanostructured rods based on the auto-association of maghemite nanoparticles and block-copolymers is probed by optical microscopy under rotating fields in a simple liquid. The re-orientation of the rods by a field rotated by 90° is first studied. The measured relaxation is characteristic of paramagnetic objects. Under a stationary rotating field, a synchronous rotational regime is observed at low field frequency. Above a frequency threshold which scales as H2, the dynamics becomes asynchronous with back-and-forth rotations. These behaviors are well predicted by the presented model.

Research Highlights►We explore the rotational dynamics of hybrid paramagnetic nanorods. ►They are based on γ-Fe2O3 nanoparticles glued together with di-block copolymers. ►They re-orientate as paramagnetic rods under a magnetic field rotated by 90°. ►Under rotating magnetic fields of low pulsation ω, they rotate synchroneously. ►Above a critical pulsation, back-and-forth dynamics and localized mode are observed.