Alternating current magnetic susceptibility of a ferronematic

Abstract

We report on experimental studies focusing on the dynamic ac magnetic susceptibility of a ferronematic. It has been shown recently, that in the isotropic phase of a ferronematic, a weak dc bias magnetic field of a few oersteds increases the ac magnetic susceptibility. This increment vanishes irreversibly if the substance is cooled down to the nematic phase, but can be reinduced by applying the dc bias field again in the isotropic phase [Tomašovičová, N. et al. Soft Matter2016, 12, 5780-5786]. The effect has no analogue in the neat host liquid crystal. Here, we demonstrate that by doubling the concentration of the magnetic nanoparticles, the range of the dc bias magnetic field to which the ferronematic is sensitive without saturation can be increased by about two orders of magnitude. This finding paves a way to application possibilities, such as low magnetic field sensors, or basic logical elements for information storage.

Keywords: ac magnetic susceptibility; ferronematics; magnetic particles.

Figure 1

Magnetization curve of the powder of Fe₃O₄ magnetic nanoparticles, measured at 285 K.

Figure 2

Temperature dependence of the capacitance of 6CB and of two ferronematic samples with different MNP concentrations, .

Figure 3

Magnetization curves of neat 6CB and the FN with a MNP concentration of = 10⁻⁴ in the nematic phase, as well as of the FN with a higher concentration of MNPs ( = 2 × 10⁻⁴ ) in the nematic (285 K) and isotropic (315 K) phases.

Figure 4

Temperature dependence of the real part χ′ of the ac susceptibility of the 6CB-based FN, measured in a cooling–heating cycle, after applying and switching off a dc magnetic field H_dc of (a) 1–6 Oe, (b) 7–100 Oe and (c) 100–2000 Oe. Solid symbols stand for cooling, while open symbols stand for heating.

Figure 5

Magnitude of the reduction in the ac susceptibility Δχ′ at the isotropic-to-nematic phase transition as a function of the dc bias magnetic field.