Dynamic magnetic response of ferrofluids under a static electric field

Magnetic nanoparticles in a non-polar ferrofluid can reassemble in external electric fields. The resulting electric field-driven structural changes in ferrofluids are expected to influence the magnetic response of ferrofluids to an alternating magnetic field. Hence, it should be possible to control the magnetic susceptibility of ferrofluids by electric forces. To address the problem of a possible electro-magnetic coupling, a low-frequency alternating current magnetic susceptibility of a ferrofluid based on insulating oil and iron oxide nanoparticles is measured under a static electric field. The electric field is generated by applying a voltage on a pair of electrodes embracing the ferrofluid and acts parallel and perpendicular to the probing alternating magnetic field. The susceptibility is measured simultaneously with the ferrofluid's temperature and a leakage current. A noticeable susceptibility decrease with increasing voltage is found. The susceptibility decrease is partially caused by the temperature increase. Based on theoretical calculations, it is found that the detected temperature increase cannot be the only reason for the measured susceptibility decrease. Other mechanisms resulting from magnetic nanoparticle interactions with the electric field (nanoparticle trapping due to dielectrophoresis, electric field-induced nanoparticle aggregation) must contribute to the susceptibility drop in a static electric field.

Automated summary

Magnetic nanoparticles in a non-polar ferrofluid can reassemble in external electric fields, influencing the magnetic response of ferrofluids. Under a static electric field, the magnetic susceptibility of a ferrofluid based on insulating oil and iron oxide nanoparticles decreases with increasing voltage, partially due to temperature increase. Other mechanisms such as nanoparticle trapping and aggregation induced by the electric field also contribute to the susceptibility drop.