Ferromagnetism in suspensions of magnetic platelets in liquid crystal

Mertelj, Alenka; Lisjak, Darja; Drofenik, Miha; Čopič, Martin

doi:10.1038/nature12863

Cited by 270 publications

(291 citation statements)

References 28 publications

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“…This is often achieved by coating the surface with monomolecular organic materials, surfactants (stabiliser), or ligands. For instance, oleic acid, 7,10,17,20,21,[24][25][26][27] selenium docosane 28 and dodecylbenzenesulphonic acid 29,30 have been widely utilized for the coating of NPs.…”

Section: Reznikov Et Al Have Shown That a Low Concentration Of Ferromentioning

confidence: 99%

A comparison between size dependent paraelectric and ferroelectric BaTiO3 nanoparticle doped nematic and ferroelectric liquid crystals

Al-Zangana

Turner

Dierking

2017

Journal of Applied Physics

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The electro-optic and dielectric properties of barium titanate, BaTiO 3 , nanoparticle (NP) doped nematic and ferroelectric liquid crystal materials were examined with respect to different size and concentration of the NPs. Smaller size paraelectric NPs (≈80nm) are compared to larger, ferroelectric NPs (≈240nm). It is found that for concentrations larger than 0.5vol% the ferroelectric NPs exhibit an increasing effect on the electro-optic response of the nematic liquid crystal, which is demonstrated by the enhancement of the dielectric anisotropy. This could be induced by the coupling of the electrical dipole moments in the spherical NPs with the LC director field. The electro-optical properties of the SmC* phase, like tilt angle Θ, switching time and spontaneous polarisation are found to be independent of the concentration and size of the NPs. The rotational viscosity calculated from response times, polarization reversal current and dielectric properties is comparable for all three methods employed and practically independent of particle concentration and size. The relaxation frequency of the Goldstone mode is higher in the ferroelectric NPs suspensions of 2.0vol% as compared to the smaller paraelectric NPs.

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Section: Reznikov Et Al Have Shown That a Low Concentration Of Ferromentioning

confidence: 99%

A comparison between size dependent paraelectric and ferroelectric BaTiO3 nanoparticle doped nematic and ferroelectric liquid crystals

Al-Zangana

Turner

Dierking

2017

Journal of Applied Physics

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“…However, due to their weak diamagnetism, most liquid crystal devices are mainly driven by electric fields. Mixtures of liquid crystals and * emmanuelle.lacaze@insp.jussieu.fr ferronematic colloidal particles, the so-called ferronematics, have been the subject of a number of experimental and theoretical studies, related to modifications of liquid crystal magnetic [1][2][3][4][5] and electrical properties [6][7][8][9][10] in the presence of a magnetic field and the recent evidence of possible formation of ferromagnetic behavior in the presence of magnetic nano-platelets [11]. One main idea of ferronematics is to enhance the weak diamagnetic response of liquid crystals, which is associated with a large magnetic Fredericksz threshold field, of the order of 1-10 kG.…”

Section: Introductionmentioning

confidence: 99%

Influence of a dispersion of magnetic and nonmagnetic nanoparticles on the magnetic Fredericksz transition of the liquid crystal 5CB

et al. 2017

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Long time ago, Brochard and de Gennes predicted the possibility of significantly decreasing the critical magnetic field of the Fredericksz transition (the magnetic Fredericksz threshold) in a mixture of nematic liquid crystals and ferromagnetic particles, the so-called ferronematics. This phenomenon has rarely been measured, usually due to soft homeotropic anchoring induced at the nanoparticle surface. Here we present an optical study of the magnetic Fredericksz transition combined with a light scattering study of the classical nematic liquid crystal, 5CB, doped with 6 nm diameter magnetic and non-magnetic nanoparticles. Surprisingly, for both nanoparticles, we observe at room temperature a net decrease of the threshold field of the Fredericksz transition at low nanoparticle concentrations, which appears associated with a coating of the nanoparticles by a brush of polydimethylsiloxane copolymer chains inducing planar anchoring of the director on the nanoparticle surface. Moreover the magnetic Fredericksz threshold exhibits non-monotonic behaviour as a function of the nanoparticle concentration for both types of nanoparticles, first decreasing down to a value from 23% to 31% below that of pure 5CB, then increasing with a further increase of nanoparticle concentration. This is interpreted as an aggregation starting at around 0.02 weight fraction that consumes more isolated nanoparticles than those introduced when the concentration is increased above c = 0.05 weight fraction (volume fraction 3.5 × 10−2 ). This shows the larger effect of isolated nanoparticles on the threshold with respect to aggregates. From dynamic light scattering measurements we deduced that, if the decrease of the magnetic threshold when the nanoparticle concentration increases is similar for both kinds of nanoparticles, the origin of this decrease is different for magnetic and non-magnetic nanoparticles. For non-magnetic nanoparticles, the behavior may be associated with a decrease of the elastic constant due to weak planar anchoring. For magnetic nanoparticles there are non-negligible local magnetic interactions between liquid crystal molecules and magnetic nanoparticles, leading to an increase of the average order parameter. This magnetic interaction thus favors an easier liquid crystal director rotation in the presence of external magnetic field, able to reorient the magnetic moments of the nanoparticles along with the molecules.

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“…Previous investigations on liquid crystal based magnetic systems were directed towards nanoparticles [24,25] and observed optic [24] and magneto-optic effects [26], but also rod-like magnetic particles [27]. More recently, ferromagnetism and ferromagnetic ordering was demonstrated for magnetic platelets [26,28,29].…”

Section: Introductionmentioning

confidence: 99%

Ordering of ferromagnetic nanoparticles in nematic liquid crystals

et al. 2017

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Dispersions of magnetic nanoparticles in a nematic liquid crystal were investigated as magnetic fields were applied in three different boundary condition geometries: (i) planar substrates and B n, (ii) planar substrates and B n, and (iii) homeotropic substrates and B n. Particle chaining is observed when a magnetic field is applied, with a periodicity perpendicular to the chains.Furthermore, linear chains are observed for the magnetic field applied perpendicular to the director, while zigzag chains are formed when the magnetic field direction is parallel to the director field. This is attributed to a change from a dipolar defect configuration around dispersed nanoparticles, to a quadrupolar one, i.e. the change from satellite to Saturn-ring defects. This effect is largely independent of the sample thickness. The dynamic development of the chain length, as well as their two-dimensional order parameter was studied in all cases. Chain lengths increased rapidly until saturation at approximately l=30 m after a time of about t=10s. Similarly, the chain order parameters increased until saturation between S=0.8-0.9, independent of sample geometry.

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Ferromagnetism in suspensions of magnetic platelets in liquid crystal

Cited by 270 publications

References 28 publications

A comparison between size dependent paraelectric and ferroelectric BaTiO3 nanoparticle doped nematic and ferroelectric liquid crystals

A comparison between size dependent paraelectric and ferroelectric BaTiO3 nanoparticle doped nematic and ferroelectric liquid crystals

Influence of a dispersion of magnetic and nonmagnetic nanoparticles on the magnetic Fredericksz transition of the liquid crystal 5CB

Ordering of ferromagnetic nanoparticles in nematic liquid crystals

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