Name: measuring magnetically-tuned ferroelectric polarization in liquid crystals
Uploaded: 2018-08-15T14:45:00
Description: Watch this Scientific Journal Video about Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals at JoVE.com

We thank Prof. Takanishi for his help in our experiment. We also thank DIC Corporation for providing the compounds studied here. This work was supported by Grant-in-Aid for the JSPS Fellow (16J02711), JSPS KAKENHI Grant Number 17H01143, and the Program for Leading Graduate Schools &#34;Interactive Materials Cadet Program&#34;.

1. Preparation of Liquid-Crystal Cells and the Determination of the Cell Gap
<ol>
	<li>Preparation of liquid-crystal cells 
	<ol>
		<li>Cut glass substrates coated with indium/tin-oxide (ITO) on one side into the desired size (typical size: 10 x 10 x 1.1 mm, Figure 2A). To cut the substrates, scratch a line on their face with a glass cutter and break off excess glass manually.</li>
		<li>Wash the cut glass substrates using a detergent in an ultrasonic bath at 35 kHz for 30...

<ol>
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H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurements+of+empty+cell+gap+for+liquid-crystal+displays+using+interferometric+methods.">Measurements of empty cell gap for liquid-crystal displays using interferometric methods.</a> Journal of Applied Physics. 64 (9), 4780-4781 (1988).</li><li>Born, M., Wolf, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Principles of Optics. , (1987).</li><li>Dierking, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Textures of Liquid Crystals. , (2003).</li><li>Filipi&#269;, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dielectric+properties+near+the+smectic-C*+-smectic-A+phase+transition+of+some+ferroelectric+liquid-crystalline+systems+with+a+very+large+spontaneous+polarization.">Dielectric properties near the smectic-C* -smectic-A phase transition of some ferroelectric liquid-crystalline systems with a very large spontaneous polarization.</a> Physics Review A. 38, 5833-5839 (1988).</li><li>Carlsson, T., &#381;ek&#353;, B., Filipi&#269;, C., Levstik, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Theoretical+model+of+the+frequency+and+temperature+dependence+of+the+complex+dielectric+constant+of+ferroelectric+liquid+crystals+near+the+smectic-C*+-smectic-A+phase+transition.">Theoretical model of the frequency and temperature dependence of the complex dielectric constant of ferroelectric liquid crystals near the smectic-C* -smectic-A phase transition.</a> Physics Review A. 42, 877-889 (1990).</li><li>Michelson, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physical+realization+of+a+Lifshitz+point+in+liquid+crystals.">Physical realization of a Lifshitz point in liquid crystals.</a> Physical Review Letters. 39, 464 (1977).</li><li>Mu&#353;evi&#269;, I., &#381;ek&#353;, B., Blinc, R., Rasing, T., Wyder, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phase+diagram+of+a+ferroelectric+chiral+smectic+liquid+crystal+near+the+Lifshitz+point.">Phase diagram of a ferroelectric chiral smectic liquid crystal near the Lifshitz point.</a> Physical Review Letters. 48, 192 (1982).</li><li>Mu&#353;evi&#269;, I., &#381;ek&#353;, B., Blinc, R., Rasing, T., Wyder, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dielectric+study+of+the+modulated+smectic+C*-uniform+smectic+C+transition+in+a+magnetic+field.">Dielectric study of the modulated smectic C*-uniform smectic C transition in a magnetic field.</a> Physica Status Solidi(b). 119, 727-733 (1983).</li><li>Blinc, R., Mu&#353;evi&#269;, I., &#381;ek&#353;, B., Seppen, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ferroelectric+liquid+crystals+in+a+static+magnetic+field.">Ferroelectric liquid crystals in a static magnetic field.</a> Physica Scripta. 35, 38-43 (1991).</li><li>Blinov, L. 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The experimental results showed that the methods described here successfully demonstrated the ME coupling in the liquid crystal. The observed ME and magneto-dielectric effects can be associated with the orientational transition of molecular orientation in a fixed smectic layer structure. However, the layer normal direction n0 in the layer structure can be also changed by applying a magnetic field through magnetic anisotropy. This is because the molecules prefer to have a parallel arra...

Research on the magnetoelectric (ME) effect, the induction of electric polarization (magnetization) by a magnetic (electric) field, has been focused towards the novel types of applications such as sensors and storage technologies. With recent studies on ME multiferroics1,2,3,4, the target systems in the field of ME study are extended to various types of solid-state materials, including inorganic, organic, and metal-organic frameworks, by utilizing spin-lattice couplings dexterously5,6,7,8,9. However, room-temperature operation, which must be accomplished for practical utilization of ME materials with their ME couplings, is still a challenging issue, and a very limited number of single-phase materials have been reported as room-temperature magnetoelectrics to date10.
Liquid crystals, which possess an orientational order, sometimes with a partial positional one, have also been examined with respect to ME materials in recent years11,12,13,14,15. One of the advantages of liquid crystals as ME materials is their operation temperature, as liquid-crystal phases are typically stabilized around room temperature. An example of ME liquid crystals reported so far is a composite between magnetic nano-platelets with perpendicular magnetic anisotropy and liquid crystals showing the nematic phase, known as the simplest liquid-crystal phase possessing only one-dimensional orientational order15. It shows the converse ME effect, the induction of magnetization by an electric field, through the electric-field manipulation of the coupled platelet and molecular orientations.
More recently, another unique strategy to establish the ME effect in liquid crystals was proposed16. The focus of this strategy is to create a chiral smectic C (SmC*) phase with one-dimensional positional order, resulting in a diffused layer structure called the smectic layer. One characteristic of the SmC* phase is that a molecular orientation vector n is coupled with a local electric dipole moment p. This correlation is provided by the combination of tilted orientation of the rod-like constituent molecules with respect to the smectic layer normal n0 and the chirality-induced mirror (and inversion) symmetry breaking in the molecules. From the viewpoint of symmetries, the former changes the symmetry from D&#8734;h (the so-called SmA phase, Figure 1A) into C2h (the so-called SmC phase, Figure 1B), and the latter breaks the mirror symmetry of C2h so that the symmetry is reduced into C2 (the SmC* phase, see each layer in Figure 1C). In each SmC* layer, the presence of finite polarization is allowed along the C2 axis, which is normal to both n0 and n. The strong coupling between n and p is essential for ferroelectricity in liquid crystals. In the SmC* phase, n aligns in the helicoidal manner through layer by layer (Figure 1C), and thus there is no macroscopic polarization. Ferroelectricity in such liquid crystals is achieved by using strong surface effects, which stabilize the homogeneously oriented state of n known as a surface-stabilized ferroelectric liquid-crystal (SSFLC) state (Figure 1D). It should be noted that ferroelectric polarization reversal always accompanies a switching of the bi-stable orientation states through the coupling between n and p17. As the inverse effect, a change in molecular orientation of the SmC* phase is expected to give rise to a change in electric polarization. Through magnetic anisotropy caused by spins on magnetic elements and/or aromatic rings in liquid-crystal molecules and the flexibility of n in a liquid-crystal state due to weaker molecular interactions than in a solid crystal state, n is also tunable by a magnetic field. Thus, the SmC* phase can be transformed into a magnetic-field-induced homogeneously oriented state similar to an SSFLC state. Therefore, the direct ME effect, the induction of electric polarization by a magnetic field, is achieved as the development of macroscopic electric polarization is induced by a homogeneous alignment of n coupled with p, in all the layers.
We introduce procedures to prepare liquid-crystal cells for the investigation of ME couplings and methodologies to detect the ME effect. A method for the preparation of liquid-crystal cells was reported in detail previously18. Here, we modified this method for dielectric and ME measurements. With the method detailed here, we detected magnetically-tuned electric polarization, that is, the direct ME effect, in a liquid crystal showing the SmC* phase at room temperature.

<table>
	<tbody>
		<tr>
			<td>Material</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Compound 1: Figure 4(A)</td>
			<td>DIC Co., Ltd.</td>
			<td>&#8211;N/A</td>
			<td>PYP-8O8</td>
		</tr>
		<tr>
			<td>Compound 2: Figure 4(B)</td>
			<td>DIC Co., Ltd.</td>
			<td>N/A</td>
			<td>PYP-10O10F</td>
		</tr>
		<tr>
			<td>ITO-coated glass substrates</td>
			<td>Sigma-Aldrich Inc.</td>
			<td>703192-10PK</td>
			<td></td>
		</tr>
		<tr>
			<td>Detergent</td>
			<td>Wako Pure Chemical Industries, Ltd.</td>
			<td>031-10401</td>
			<td></td>
		</tr>
		<tr>
			<td>Alignment layer planer</td>
			<td>JSR Co., Ltd.</td>
			<td>AL1254</td>
			<td></td>
		</tr>
		<tr>
			<td>Spacer</td>
			<td>Teijin Film Solutions Co., Ltd.</td>
			<td>Q51-12</td>
			<td></td>
		</tr>
		<tr>
			<td>Glue</td>
			<td>Huntsman Inc.</td>
			<td>ARALDITE RT30</td>
			<td>For gluing two substrates</td>
		</tr>
		<tr>
			<td>Glue</td>
			<td>M&#38;I Materials ltd.</td>
			<td>Apiezon H Grease</td>
			<td>For gluing a cell and homemade insert</td>
		</tr>
		<tr>
			<td>Silver paste</td>
			<td>Fujikura Kasei Co., Ltd.</td>
			<td>D-753</td>
			<td></td>
		</tr>
		<tr>
			<td>Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrasonic cleaner</td>
			<td>AS ONE Corp.</td>
			<td>AS52GTU</td>
			<td></td>
		</tr>
		<tr>
			<td>Spin coater</td>
			<td>Mikasa Co. Ltd.</td>
			<td>1H-D7</td>
			<td></td>
		</tr>
		<tr>
			<td>Polarized optical microscope</td>
			<td>Nikon Co., Ltd.</td>
			<td>ECLIPSE LV100N POL</td>
			<td></td>
		</tr>
		<tr>
			<td>Short-pass filter</td>
			<td>Thorlabs Inc.</td>
			<td>FB600-40</td>
			<td></td>
		</tr>
		<tr>
			<td>Optical spectrometer</td>
			<td>Ocean Optics Inc.</td>
			<td>USB2000+UV-VIS</td>
			<td></td>
		</tr>
		<tr>
			<td>Differential thermal analyzer</td>
			<td>Rigaku Co., Ltd.</td>
			<td>Thermo plus EVO2</td>
			<td></td>
		</tr>
		<tr>
			<td>Superconducting magnet</td>
			<td>Quantum Design Inc.</td>
			<td>PPMS</td>
			<td></td>
		</tr>
		<tr>
			<td>LCR meter</td>
			<td>Keysight Technologies Ltd.</td>
			<td>E4980A</td>
			<td></td>
		</tr>
		<tr>
			<td>Electrometer</td>
			<td>Keithley Instruments Inc.</td>
			<td>6517A</td>
			<td></td>
		</tr>
	</tbody>
</table>

measuring magnetically-tuned ferroelectric polarization in liquid crystals

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due to their potential applications for future device technologies such as sensors and storage. However, conventional approaches, which usually utilize materials containing magnetic metal ions (or radicals), have a major problem: only a few materials have been found to show the coupling phenomena at room temperature. Recently, we proposed a new approach to achieve room-temperature magnetoelectrics. In contrast to conventional approaches, our alternative proposal focuses on a completely different material, a &#34;liquid crystal&#34;, free from magnetic metal ions. In such liquid crystals, a magnetic field can be utilized to control the orientational state of constituent molecules and the corresponding electric polarization through magnetic anisotropy of the molecules; it is an unprecedented mechanism of the magnetoelectric effect. In this context, this paper provides a protocol to measure ferroelectric properties induced by a magnetic field, that is, the direct magnetoelectric effect, in a liquid crystal. With the method detailed here, we successfully detected magnetically-tuned electric polarization in the chiral smectic C phase of a liquid crystal at room temperature. Taken together with the flexibility of constituent molecules, which directly affects the magnetoelectric responses, the introduced method will serve to allow liquid crystal cells to acquire more functions as room-temperature magnetoelectrics and associated optical materials.

The protocol is deemed a success only if the ME effect in liquid-crystal samples is observed. Here we measured the direct ME effect in a liquid-crystal sample prepared by the aforementioned procedures. For the measurements, an in-plane magnetic field was applied with the angle tilted by about 45&#176; from the rubbing direction (normal to smectic layers), because the largest magnetic-field-induced polarization was detected in this configuration16.
<p class="jov...

Watch this Scientific Journal Video about Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals at JoVE.com

Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals

In this report, we present a protocol to examine direct magnetoelectric effects, i.e., induction of ferroelectric polarization by applying magnetic fields, in liquid crystals. This protocol provides a unique approach, supported by the softness of liquid crystals, to achieve room-temperature magnetoelectrics.

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due ...

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