Name: measuring magnetically-tuned ferroelectric polarization in liquid crystals
Uploaded: 2018-08-15T14:45:00.000+00:00
Duration: 7 min 3 s
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 min. Rinse them with deionized water in the ultrasonic bath for 10 min. Replace deionized water and rinse the substrates 5 times to remove contaminants (Figure 2B). Blow off remaining water with an air-duster-gun with care not to touch the widest faces of the substrates.</li>
		<li>Drip polyimide solutions (alignment layer planer in Table of Materials) onto the ITO-coated side of the washed substrates, and spin-coat the solutions at 5000 rpm for 30 s (Figure 2C). Bake the substrates at 200 &#176;C for 1 h to remove the solvent and cure the polyimide thin films.</li>
		<li>Put the substrates on an XZ stage so that the ITO- and polyimide-coated side of the substrates faces upwards. Place the substrates under a roller covered with a velvet cloth and fix the substrates by air suctioning (Figure 2D). Apply a uniform and soft pressure on the substrates with the roller by adjusting the height of the stage. 
		Note: Here, the XZ stage was made by a machine shop at Osaka University.</li>
		<li>Rotate the roller and move the stage back and forth under the roller 5 times along the horizontal direction to rub the substrates by the velvet cloth. Dip the rubbed substrates into isopropyl alcohol in a 10 &#8211; 50 mL glass container for 1 min to remove contaminants, and dry them at 80 &#176;C for a few minutes.</li>
		<li>Glue the two substrates together with 12 &#956;m thickness flat resin films as spacers. Note that adhesive points are placed only at the edge of the substrates and the inner sides of the glued substrates are coated with the ITO and polyimide. Make sure that the opposite substrates have been rubbed antiparallel and are slightly shifted (about 2 mm) to provide enough spaces for electrical terminals on both of the substrates (Figure 2E).</li>
		<li>Glue the conducting wires on the above-mentioned spaces for terminals by using silver conducting paste (Figure 2F). Bake the substrates with conductive wires at 150 &#176;C for 1 h to remove the solvent in the silver conductive paste.</li>
	</ol>
	</li>
	<li>Determination of cell gap19
	<ol>
		<li>Irradiate the blank cells prepared in 1.1.7 with white light propagating normal to their widest face. Measure the transmission spectra using an optical spectrometer, and observe pseudo-sinusoidal oscillation (Figure 3), which appears due to the Fabry-P&#233;rot effect20.</li>
		<li>Estimate the cell gap d by using the relationship d = &#955;1&#955;2/2(&#955;2-&#955;1), where the wavelengths &#955;1 and &#955;2 denote a pair of adjacent peak-wavelengths in the transmission spectra.</li>
	</ol>
	</li>
</ol>
2. Preparation of the Liquid-crystal Mixture and Introduction into the Cells
<ol>
	<li>Mix two compounds, 5-octyl-2-(4-octyloxyphenyl) pyrimidine (compound 1: Figure 4A) and (S)-5-decyl-2-[4(2-fluorodecyloxy) phenyl] pyrimidine (compound 2: Figure 4B) with a mass ratio of 3:1 in a glass vial. Prepare 100 mg of the solution in total (75 mg of compound 1 and 25 mg of compound 2).</li>
	<li>Put the prepared blank cell from step 1.1.7 on a hot stage, keeping the temperature at 80 &#176;C, a temperature at which the mixture from 2.1 is in the isotropic liquid phase (Figure 5). Introduce the mixture from step 2.1 into the cell by using a spatula and capillary action. Keep the cell temperature at 80 &#176;C for 30 min, then cool down to room temperature at a rate of about 5 &#176;C/min.</li>
</ol>
3. Sample Characterization
<ol>
	<li>Place a cell filled with the mixture from step 2.2 on a hot stage between two crossed polarizers and irradiate it with light. Observe textures of the mixture with changing temperature from room temperature to 80 &#176;C at a rate of 5 &#176;C/min by using a microscope (and a short-pass filter with tuning range of ~600 nm to enhance the visibility, as necessary), and identify liquid-crystal phases from polarization micrographs21 (Figure 6).</li>
	<li>Determine the phase transition sequence and transition temperatures from the observed textures (Figure 5). For the SmC* phase, estimate the helicoidal pitch as double the stripe width.</li>
	<li>Confirm the first-order phase transition temperatures of the mixture prepared in 2.1 by differential thermal analysis (DTA; see Table of Materials and manufacturer&#8217;s instructions), which provides a peak (or dip) anomaly at a first-order phase transition (Figure 7).</li>
</ol>
4. Dielectric and Magnetoelectric Measurements
<ol>
	<li>Prepare a commercial superconducting magnet (see Table of Materials) equipped with temperature controllers (2 - 400 K) and magnetic field (up to 9 T).</li>
	<li>Prepare a homemade insert for the superconducting magnet, which consists of three major parts: sample space, a rod including four coaxial cables, and a connector terminal (Figure 8A).</li>
	<li>Glue the cell prepared in 2.2 on the sample space of the insert (Figure 8B). Connect the two conductive wires of the cell to the terminals (high and low) of the sample space by soldering. Make sure of the cell orientation so as to apply a magnetic field in the direction parallel to the substrates of the cell. Place a thermometer on the widest plane of the cell in order to measure the sample temperature accurately and introduce the insert into the superconducting magnet.</li>
	<li>Connect the connecter terminals to an LCR meter (see Table of Materials) with coaxial cables. Measure the dielectric constant as a function of temperature and magnetic field by means of quasi-four terminal methods with the LCR meter (see manufacturer&#8217;s instructions and our previous work16).</li>
	<li>Connect the connecter terminals to an electrometer (see Table of Materials) with coaxial cables. Measure the magnetic-field and temperature dependence of displacement current with the electrometer while sweeping a magnetic field and temperature at a constant rate (1.0 T/min for sweeping magnetic field and 5 K/min for sweeping temperature; see manufacturer&#8217;s instructions and our previous work16). Obtain electric polarization by integrating the displacement current as a function of time.</li>
</ol>

<ol>
	<li>Eerenstein, W., Mathur, N. D., Scott, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiferroic+and+magnetoelectric+materials.">Multiferroic and magnetoelectric materials.</a> Nature. 442, 759-765 (2006).</li><li>Cheong, S. -. W., Mostovoy, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiferroics:+A+magnetic+twist+for+ferroelectricity.">Multiferroics: A magnetic twist for ferroelectricity.</a> Nature Materials. 6, 13-20 (2007).</li><li>Tokura, Y., Seki, S., Nagaosa, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiferroics+of+spin+origin.">Multiferroics of spin origin.</a> Reports on Progress in Physics. 77, 076501 (2014).</li><li>Fiebig, M., Lottermoser, T., Meier, D., Trassin, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+evolution+of+multiferroics.">The evolution of multiferroics.</a> Nature Reviews Materials. 1, 16046 (2016).</li><li>Kagawa, F., Horiuchi, S., Tokunaga, M., Fujioka, M., Tokura, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ferroelectricity+in+a+one-dimensional+organic+quantum+magnet.">Ferroelectricity in a one-dimensional organic quantum magnet.</a> Nature Physics. 6, 169-172 (2010).</li><li>Stroppa, A., 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=Electric+Control+of+magnetization+and+interplay+between+orbital+ordering+and+ferroelectricity+in+a+multiferroic+metal-organic+framework.">Electric Control of magnetization and interplay between orbital ordering and ferroelectricity in a multiferroic metal-organic framework.</a> Angewandte Chemie International Edition. 50, 5847-5850 (2011).</li><li>Wang, W., 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=Magnetoelectric+coupling+in+the+paramagnetic+state+of+a+metal-organic+framework.">Magnetoelectric coupling in the paramagnetic state of a metal-organic framework.</a> Science Reports. 3, 2024 (2011).</li><li>G&#243;mez-Aguirre, L. 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=Magnetic+ordering-induced+multiferroic+behavior+in+[CH3NH3][Co(HCOO)3]+metal-organic+framework.">Magnetic ordering-induced multiferroic behavior in [CH3NH3][Co(HCOO)3] metal-organic framework.</a> Journal of the American Chemical Society. 138, 1122-1125 (2016).</li><li>Qin, W., Xu, B., Ren, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+organic+approach+for+nanostructured+multiferroics.">An organic approach for nanostructured multiferroics.</a> Nanoscale. 7, 9122-9132 (2015).</li><li>Scott, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Room-temperature+multiferroic+magnetoelectrics.">Room-temperature multiferroic magnetoelectrics.</a> NPG Asia Materials. 5, e72 (2013).</li><li>Suzuki, K., 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=Influence+of+applied+electric+fields+on+the+positive+magneto-LC+effects+observed+in+the+ferroelectric+liquid+crystalline+phase+of+a+chiral+nitroxide+radical+compound.">Influence of applied electric fields on the positive magneto-LC effects observed in the ferroelectric liquid crystalline phase of a chiral nitroxide radical compound.</a> Soft Matter. 9, 4687-4692 (2013).</li><li>Domracheva, N. E., Ovchinnikov, I. V., Turanov, A. N., Konstantinov, V. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=EPR+detection+of+presumable+magnetoelectric+interactions+in+the+liquid-crystalline+state+of+an+iron+mesogen.">EPR detection of presumable magnetoelectric interactions in the liquid-crystalline state of an iron mesogen.</a> Journal of Magnetism and Magnetic Materials. 269, 385-392 (2004).</li><li>Toma&#353;ovi&#269;ov&#225;, N., 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=Capacitance+changes+in+ferronematic+liquid+crystals+induced+by+low+magnetic+fields.">Capacitance changes in ferronematic liquid crystals induced by low magnetic fields.</a> Phys. Rev. E. 87, 014501 (2013).</li><li>Lin, T. -. J., Chen, C. -. C., Lee, W., Cheng, S., Chen, Y. -. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrical+manipulation+of+magnetic+anisotropy+in+the+composite+of+liquid+crystals+and+ferromagnetic+nanorods.">Electrical manipulation of magnetic anisotropy in the composite of liquid crystals and ferromagnetic nanorods.</a> Applied Physics Letters. 93, 013108 (2008).</li><li>Mertelj, A., Osterman, N., Lisjak, D., &#268;opi&#269;, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Magneto-optic+and+converse+magnetoelectric+effects+in+a+ferromagnetic+liquid+crystal.">Magneto-optic and converse magnetoelectric effects in a ferromagnetic liquid crystal.</a> Soft Matter. 10, 9065-9072 (2014).</li><li>Ueda, H., Akita, T., Uchida, Y., Kimura, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Room-temperature+magnetoelectric+effect+in+a+chiral+smectic+liquid+crystal.">Room-temperature magnetoelectric effect in a chiral smectic liquid crystal.</a> Applied Physics Letters. 111, 262901 (2017).</li><li>Clark, N. A., Lagerwall, S. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Submicrosecond+bistable+electro-optic+switching+in+liquid+crystals.">Submicrosecond bistable electro-optic switching in liquid crystals.</a> Applied Physics Letters. 36, 899-901 (1980).</li><li>Vantomme, G., Gelebart, A. H., Broer, D. J., Meijer, E. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+liquid+crystal+networks+for+macroscopic+oscillatory+motion+induced+by+light.">Preparation of liquid crystal networks for macroscopic oscillatory motion induced by light.</a> Journal of Visualized Experiments. (127), e56266 (2017).</li><li>Yang, K. 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. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Electrooptical and Magnetooptical Properties of Liquid Crystals. , (1983).</li></ol>

The authors have nothing to disclose.

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>&lt;strong&gt;Material&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Compound 1: Figure 4(A)</td><td>DIC Co., Ltd.</td><td>&amp;ndash;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&amp;amp;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>&lt;strong&gt;Equipment&lt;/strong&gt;</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 ...

measuring-magnetically-tuned-ferroelectric-polarization-liquid

Research

JoVE Journal

Engineering

8.7K Views.  Osaka University. 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.

Video: Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals

Chemical Vapor Deposition of an Organic Magnet, Vanadium Tetracyanoethylene

Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in traditional materials, including low cost and mechanical flexibility. In a similar vein, it would be advantageous to expand the use of organics into high frequency electronics and spin-based electronics. This work presents a synthetic process for the growth of thin films of the room temperature organic ferrimagnet, vanadium tetracyanoethylene (V[TCNE]x, x~2) by low temperature chemical vapor deposition (CVD). The thin film is grown at &#60;60 &#176;C, and can accommodate a wide variety of substrates including, but not limited to, silicon, glass, Teflon and flexible substrates. The conformal deposition is conducive to pre-patterned and three-dimensional structures as well. Additionally this technique can yield films with thicknesses ranging from 30 nm to several microns. Recent progress in optimization of film growth creates a film whose qualities, such as higher Curie temperature (600 K), improved magnetic homogeneity, and narrow ferromagnetic resonance line-width (1.5 G) show promise for a variety of applications in spintronics and microwave electronics.

We present the synthesis of the organic-based ferrimagnet vanadium tetracyanoethylene (V[TCNE]x, x~2) via low temperature chemical vapor deposition (CVD). This optimized recipe yields an increase in Curie temperature from 400 K to over 600 K and a dramatic improvement in magnetic resonance properties.

Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in ...

Chemistry

Phase Diagram Characterization Using Magnetic Beads as Liquid Carriers

Magnetic beads with ~1.9 &#181;m average diameter were used to transport microliter volumes of liquids between contiguous liquid segments with a tube for the purpose of investigating phase change of those liquid segments. The magnetic beads were externally controlled using a magnet, allowing for the beads to bridge the air valve between the adjacent liquid segments. A hydrophobic coating was applied to the inner surface of the tube to enhance the separation between two liquid segments. The applied magnetic field formed an aggregate cluster of magnetic beads, capturing a certain liquid amount within the cluster that is referred to as carry-over volume. A fluorescent dye was added to one liquid segment, followed by a series of liquid transfers, which then changed the fluorescence intensity in the neighboring liquid segment. Based on the numerical analysis of the measured fluorescence intensity change, the carry-over volume per mass of magnetic beads has been found to be ~2 to 3 &#181;l/mg. This small amount of liquid allowed for the use of comparatively small liquid segments of a couple hundred microliters, enhancing the feasibility of the device for a lab-in-tube approach. This technique of applying small compositional variation in a liquid volume was applied to analyzing the binary phase diagram between water and the surfactant C12E5 (pentaethylene glycol monododecyl ether), leading to quicker analysis with smaller sample volumes than conventional methods.

Here, we present a protocol to investigate multi-component phase diagrams using externally controlled magnetic beads as liquid carriers in a lab-in-tube approach. This approach can aid in applications that seek to gather further information on phase change in complex liquid systems.

Magnetic beads with ~1.9 &#181;m average diameter were used to transport microliter volumes of liquids between contiguous liquid segments with a tube for ...

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

Herein, we demonstrate that a bottom-up approach, based on halogen bonding (XB), can be successfully applied for the design of a new type of ionic liquid crystals (ILCs). Taking advantages of the high specificity of XB for haloperfluorocarbons and the ability of anions to act as XB-acceptors, we obtained supramolecular complexes based on 1-alkyl-3-methylimidazolium iodides and iodoperfluorocarbons, overcoming the well-known immiscibility between hydrocarbons (HCs) and perfluorocarbons (PFCs). The high directionality of the XB combined with the fluorophobic effect, allowed us to obtain enantiotropic liquid crystals where a rigid, non-aromatic, XB supramolecular anion acts as mesogenic core.
X-ray structure analysis of the complex between 1-ethyl-3-methylimidazolium iodide and iodoperfluorooctane showed the presence of a layered structure, which is a manifestation of the well-known tendency to segregation of perfluoroalkyl chains. This is consistent with the observation of smectic mesophases. Moreover, all the reported complexes melt below 100 &#176;C, and most are mesomorphic even at room temperature, despite that the starting materials were non-mesomorphic in nature.
The supramolecular strategy reported here provides new design principles for mesogen design allowing a totally new class of functional materials.

A protocol for the synthesis of a new type of mesogens, based on the halogen-bonded supramolecular anion [CnF2n+1-I&#183;&#183;&#183;I&#183;&#183;&#183;I-CnF2n+1]&#8722;, is reported.

Herein, we demonstrate that a bottom-up approach, based on halogen bonding (XB), can be successfully applied for the design of a new type of ionic liquid ...

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve desired molecular orientation states in LC displays, the "static" surface property of LCs, so-called surface anchoring, has been intensively studied. As a rule of thumb, once the initial orientation of LCs is "locked" by specific surface treatments, such as rubbing or treatment with a specific alignment layer, it hardly changes with temperature. Here, we present a system exhibiting an orientational transition upon temperature variation, which conflicts with the consensus. Right on the transition, the bulk LC molecules experience the orientational rotation, with 90&#176; between the planar (P) orientation at high temperatures and the vertical (V) orientation at low temperatures in the first-order transitional manner. We have tracked thermodynamic surface anchoring behavior by means of polarizing optical microscopy (POM), dielectric spectroscopy (DS), high-resolution differential scanning calorimetry (HR-DSC), and grazing incidence X-ray diffraction (GI-XRD) and reached a plausible physical explanation: that the transition is triggered by a growth of surface wetting sheets, which impose the V orientation locally against the P orientation in the bulk. This landscape would provide a general link explaining how the equilibrium bulk orientation is affected by surface-localized orientation in many LC systems. In our characterization, POM and DS are advantageous by offering information on the spatial distribution of the orientation of LC molecules. HR-DSC gives information about the precise thermodynamic information on transitions, which cannot be addressed by conventional DSC instruments due to limited resolution. GI-XRD provides information on surface-specific molecular orientation and short-range orderings. The goal of this paper is to present a protocol for preparing a sample that exhibits the transition and to demonstrate how the thermodynamic structural variation, both in the bulk and on surfaces, can be analyzed through the abovementioned methods.

Here, we present a protocol to trigger an orientational transition of a liquid crystal in response to temperature. Methodologies are described for preparing a sample in order to observe the transition and the detailed transitional evolution.

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve ...

Fabrication Procedures and Birefringence Measurements for Designing Magnetically Responsive Lanthanide Ion Chelating Phospholipid Assemblies

Bicelles are tunable disk-like polymolecular assemblies formed from a large variety of lipid mixtures. Applications range from membrane protein structural studies by nuclear magnetic resonance (NMR) to nanotechnological developments including the formation of optically active and magnetically switchable gels. Such technologies require high control of the assembly size, magnetic response and thermal resistance. Mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and its lanthanide ion (Ln3+) chelating phospholipid conjugate, 1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylene triaminepentaacetate (DMPE-DTPA), assemble into highly magnetically responsive assemblies such as DMPC/DMPE-DTPA/Ln3+ (molar ratio 4:1:1) bicelles. Introduction of cholesterol (Chol-OH) and steroid derivatives in the bilayer results in another set of assemblies offering unique physico-chemical properties. For a given lipid composition, the magnetic alignability is proportional to the bicelle size. The complexation of Ln3+ results in unprecedented magnetic responses in terms of both magnitude and alignment direction. The thermo-reversible collapse of the disk-like structures into vesicles upon heating allows tailoring of the assemblies&#39; dimensions by extrusion through membrane filters with defined pore sizes. The magnetically alignable bicelles are regenerated by cooling to 5 &#176;C, resulting in assembly dimensions defined by the vesicle precursors. Herein, this fabrication procedure is explained and the magnetic alignability of the assemblies is quantified by birefringence measurements under a 5.5 T magnetic field. The birefringence signal, originating from the phospholipid bilayer, further enables monitoring of polymolecular changes occurring in the bilayer. This simple technique is complementary to NMR experiments that are commonly employed to characterize bicelles.

Fabrication procedures for highly magnetically responsive lanthanide ion chelating polymolecular assemblies are presented. The magnetic response is dictated by the assembly size, which is tailored by extrusion through nanopore membranes. The assemblies&#39; magnetic alignability and temperature-induced structural changes are monitored by birefringence measurements, a complimentary technique to nuclear magnetic resonance and small angle neutron scattering.

Bicelles are tunable disk-like polymolecular assemblies formed from a large variety of lipid mixtures. Applications range from membrane protein structural ...

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational spectroscopy and time-resolved electron diffraction. Liquid crystal phase is an important state of matter that exists between the solid and liquid phases and it is common in natural systems as well as in organic electronics. Liquid crystals are orientationally ordered but loosely packed, and therefore, the internal conformations and alignments of the molecular components of LCs can be modified by external stimuli. Although advanced time-resolved diffraction techniques have revealed picosecond-scale molecular dynamics of single crystals and polycrystals, direct observations of packing structures and ultrafast dynamics of soft materials have been hampered by blurry diffraction patterns. Here, we report time-resolved IR vibrational spectroscopy and electron diffractometry to acquire ultrafast snapshots of a columnar LC material bearing a photoactive core moiety. Differential-detection analyses of the combination of time-resolved IR vibrational spectroscopy and electron diffraction are powerful tools for characterizing structures and photoinduced dynamics of soft materials.

Here, we present the protocols of differential-detection analyses of time-resolved infrared vibrational spectroscopy and electron diffraction which enable observations of the deformations of local structures around photoexcited molecules in a columnar liquid crystal, giving an atomic perspective on the relationship between the structure and the dynamics of this photoactive material.

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational ...

A Fabrication and Measurement Method for a Flexible Ferroelectric Element Based on Van Der Waals Heteroepitaxy

Flexible non-volatile memories have received much attention as they are applicable for portable smart electronic device in the future, relying on high-density data storage and low-power consumption capabilities. However, the high-quality oxide based nonvolatile memory on flexible substrates is often constrained by the material characteristics and the inevitable high-temperature fabrication process. In this paper, a protocol is proposed to directly grow an epitaxial yet flexible lead zirconium titanate memory element on muscovite mica. The versatile deposition technique and measurement method enable the fabrication of flexible yet single-crystalline non-volatile memory elements necessary for the next generation of smart devices.

In this paper, we present a protocol to directly grow an epitaxial yet flexible lead zirconium titanate memory element on muscovite mica.

Flexible non-volatile memories have received much attention as they are applicable for portable smart electronic device in the future, relying on ...

An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation

We demonstrate a method for fabricating a prototype reflective display device that contains cholesteric liquid crystal (LC) as an active component. The cholesteric LC is composed of a nematic LC 4&#39;-pentyloxy-4-cyanobiphenyl (5OCB), redox-responsive chiral dopant (FcD), and a supporting electrolyte 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIm-OTf). The most important component is FcD. This molecule changes its helical twisting power (HTP) value in response to redox reactions. Therefore, in situ electrochemical redox reactions in the LC mixture allow for the device to change its reflection color in response to electrical stimuli. The LC mixture was introduced, by a capillary action, into a sandwich-type ITO glass cell comprising two glass slides with patterned indium tin oxide (ITO) electrodes, one of which was coated with poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) doped with perchlorate (PEDOT+). Upon application of +1.5 V, the reflection color of the device changed from blue (467 nm) to green (485 nm) in 0.4 s. Subsequent application of 0 V made the device recover the original blue color in 2.7 s. This device is characterized by its fastest electrical response and lowest operating voltage among any previously reported cholesteric LC device. This device could pave the way for the development of next generation reflective displays with low energy consumption rates.

A protocol for the fabrication of a reflective cholesteric liquid crystalline display device containing a redox-responsive chiral dopant allowing quick and low-voltage operation is presented.

We demonstrate a method for fabricating a prototype reflective display device that contains cholesteric liquid crystal (LC) as an active component. The ...

Spectral and Angle-Resolved Magneto-Optical Characterization of Photonic Nanostructures

Photonic crystals are periodic nanostructures that can support a variety of confined electromagnetic modes. Such confined modes are usually accompanied by local enhancement of electric field intensity that strengthens light-matter interactions, enabling applications such as surface-enhanced Raman scattering (SERS) and surface plasmon enhanced sensing. In the presence of magneto-optically active materials, the local field enhancement gives rise to anomalous magneto-optical activity. Typically, the confined modes of a given photonic crystal depend strongly on the wavelength and incidence angle of the incident electromagnetic radiation. Thus, spectral and angular-resolved measurements are needed to fully identify them as well as to establish their relationship with the magneto-optical activity of the crystal. In this article, we describe how to use a Fourier-plane (back focal plane) microscope to characterize magneto-optically active samples. As a model system, here we use a plasmonic grating built out of magneto-optically active Au/Co/Au multilayer. In the experiments, we apply a magnetic field on the grating in situ and measure its reciprocal space response, obtaining the magneto-optical response of the grating over a range of wavelengths and incident angles. This information enables us to build a complete map of the plasmonic band structure of the grating and the angle and wavelength dependent magneto-optical activity. These two images allow us to pinpoint the effect that the plasmon resonances have on the magneto-optical response of the grating. The relatively small magnitude of magneto-optical effects requires a careful treatment of the acquired optical signals. To this end, an image processing protocol for obtaining magneto-optical response from the acquired raw data is laid out.

Photonic band structure enables understanding how confined electromagnetic modes propagate within a photonic crystal. In photonic crystals that incorporate magnetic elements, such confined and resonant optical modes are accompanied by enhanced and modified magneto-optical activity. We describe a measurement procedure to extract the magneto-optical band structure by Fourier space microscopy.

Photonic crystals are periodic nanostructures that can support a variety of confined electromagnetic modes. Such confined modes are usually accompanied by ...

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such as on-demand switchable adhesion technologies, actuators, molecular clutches, and nano-/microscopic mass transporters. Recently it was found that through a special solid-liquid transition, rheological properties can exhibit significant changes, thus providing suitable smart viscoelastic materials. However, designing materials with such a property is complex, and forward and backward switching times are usually long. Therefore, it is important to explore new working mechanisms to realize solid-liquid transitions, shorten the switching time, and enhance the contrast of rheological properties during switching. Here, a light-induced crystal-liquid phase transition is observed, which is characterized by means of polarizing light microscopy (POM), photorheometry, photo-differential scanning calorimetry (photo-DSC), and X-ray diffraction (XRD). The light-induced crystal-liquid phase transition presents key features such as (1) fast switching of crystal-liquid phases for both forward and backward reactions and (2) a high contrast ratio of viscoelasticity. In the characterization, POM is advantageous in offering information on the spatial distribution of LC molecule orientations, determining the type of liquid crystalline phases appearing in the material, and studying the orientation of LCs. Photorheometry allows measurement of a material&#8217;s rheological properties under light stimuli and can reveal the photorheological switching properties of materials. Photo-DSC is a technique to investigate thermodynamic information of materials in darkness and under light irradiation. Lastly, XRD allows studying of microscopic structures of materials. The goal of this article is to clearly present how to prepare and measure the discussed properties of a photorheological material.

This protocol demonstrates the preparation of a photorheological material that exhibits a solid phase, various liquid crystalline phases, and an isotropic liquid phase by increasing temperature. Presented here are methods for measuring the structure-viscoelasticity relationship of the material.

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such ...