Biasing a ferronematic – a new way to detect weak magnetic field

Abstract

The magnetic properties of a ferronematic, i.e., a nematic liquid crystal doped with magnetic nanoparticles in low volume concentration are studied, with the focus on the ac magnetic susceptibility. A weak dc bias magnetic field (a few Oe) applied to the ferronematic in its isotropic phase increases the ac magnetic susceptibility considerably. Passage of the isotropic-to-nematic phase transition resets this enhancement irreversibly (unless the dc bias field is applied again in the isotropic phase).

Alternating current magnetic susceptibility of a ferronematic

“…Experimental studies on dynamics are very scarce [ 26 ], thus most theoretical predictions still await experimental justification. In a recent work [ 27 ], we investigated the response of FNs to a small alternating magnetic field, measuring the ac magnetic susceptibility. We found that, unexpectedly, a small bias magnetic field ( H dc above ca.…”

“…This increment vanished irreversibly at passing the isotropic-to-nematic phase transition on cooling (unless the bias field is applied again in the isotropic phase). A phenomenological explanation of the experimental results related this behavior to defect-mediated aggregation and magnetic-field-assisted disaggregation of MNPs [ 27 ].…”

“…In principle, the effect can provide a concept for potential future applications as sensors, or logical gates in micro- and nanodevices. However, the ferronematic composition investigated in [ 27 ] turned out to be sensitive to H dc > 8 Oe only. Moreover, the effect of the increase in the ac susceptibility saturated for H dc > 10 Oe.…”

“…Moreover, the effect of the increase in the ac susceptibility saturated for H dc > 10 Oe. Therefore, the ferronematic composition reported in [ 27 ] can serve as a logical gate with a “yes” or “no” response to a prior existence of the biasing magnetic field H dc > 8 Oe, rather than to function as a sensor that can sense and measure the magnitude of H dc .…”

Low Magnetic Field Response in Ferronematics

“…The spherical MPs were prepared by the co-precipitation method described in [8]. The rod-like MPs were synthesized through hydrolysis of FeCl 3 and FeSO 4 solutions containing urea [9]. The morphology and size distribution of the prepared nanoparticles were determined by transmission electron microscopy (TEM) [10].…”