Author name used in this publication: Siu Wing OrAuthor name used in this publication: Helen Lai Wa Chan2005-2006 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Chan, HLW

Jia, Y

Luo, H

Or, DSW

Zhao, X

Applied Physics Letters

PolyU Institutional Repository

Magnetoelectric effect in laminate composite of magnets/0.7Pb„Mg1/3Nb2/3…O3–0.3PbTiO3 single crystalYanmin JiaaState Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Instituteof Ceramics, Chinese Academy of Sciences, 215 Chengbei Road, Jiading, Shanghai 201800, China;Graduate School of the Chinese Academy of Sciences, Beijing 10039, China; and Department of AppliedPhysics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong KongXiangyong Zhao and Haosu LuoState Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Instituteof Ceramics, Chinese Academy of Sciences, 215 Chengbei Road, Jiading, Shanghai 201800, ChinaSiu Wing Or and Helen Lai Wa ChanDepartment of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong KongReceived 12 October 2005; accepted 18 February 2006; published online 4 April 2006A magnetoelectric ME laminate composite was fabricated by sandwiching one0.7PbMg1/3Nb2/3O3–0.3PbTiO3 PMN-PT piezoelectric single crystal layer between two NdFeBmagnet layers along the thickness direction. The high ME effect was obtained by the product of themagnetic attractive-repellent effect in the magnet layers and the piezoelectric effect in thepiezoelectric layer. The magnetoelectric voltage coefficient of the composite was measured to be12.5 mV/cm Oe with a flat frequency response in the range of 0.1–20 kHz. The induced MEvoltage showed an excellent linear relationship to the applied ac magnetic field with field amplitudevarying from 10−3 to 10 Oe. Other advantages included low heat generation, no bias magnetic fieldrequired, and high scale-down capability. These made the composite to be a promising ME materialfor realizing high-performance, small-size, and low-cost magnetic sensors. © 2006 AmericanInstitute of Physics. DOI: 10.1063/1.2191948The magnetoelectric ME effect is an electric polariza-tion response of a material to an applied magnetic field.1 Thiseffect has been a remarkable research topic in recent yearsdue to its important application in magnetic sensors withhigh transduction efficiency between magnetic and electricenergies. Hereinto, magnetostrictive/piezoelectric laminatecomposites, especially laminates of Terfenol-D alloy and0.7PbMg1/3Nb2/3O3–0.3PbTiO3 PMN-PT single crystal,have shown enhanced ME effect compared to single-phaseand other multiphase ME materials.2–4 While extended stud-ies concerning the ME effect in Terfenol-D/PMN-PT lami-nate composites have been published,5,6 focuses were mainlyput on obtaining good coupling between the two laminatephases. It is known that monolithic Terfenol-D suffers intrin-sically from high cost, high eddy current-induced bandwidthlimitation to a few kilohertz, and the need of an externaldc bias magnetic field to maximize its magnetostrictiveresponse.7,8 Thus, configurations of magnetic sensors basedon such laminate composites are generally complicated andnot amenable to the miniaturization.In this work, we fabricated a ME laminate composite bysandwiching one PMN-PT piezoelectric single crystal layerbetween two NdFeB magnet layers along the thickness di-rection. Figure 1 illustrates the geometry and working prin-ciple of the proposed composite. The north N and south Spoles of the magnet layers are arranged in such a way thattheir faces are normal to the thickness direction. The polar-ization direction of the piezoelectric layer is also in the thick-ness direction. The NdFeB magnet layers were commerciallysupplied in the form of a plate with 10.6 mm long, 4 mmwide, and 1 mm thickness. They were galvanized usingnickel, and their magnetic pole strength qm is known to be14.7 Wb. The PMN-PT piezoelectric layer was grown in-house by a modified Bridgman technique.9 It has the samedimensions as the magnet layers, and its thickness is orientedin the 001 direction. After being electroded with silver andpolarized along its thickness direction in a silicone oil bath,the relative dielectric constant 33T /0 of the piezoelectriclayer was evaluated to be 7990 at 1 kHz using an HP 4194Aimpedance analyzer. The piezoelectric charge coefficientd33 was measured to be 1700 pC/N using a quasistaticBerlincourt d33 meter. The piezoelectric voltage coefficientg33=d33/33T  was determined to be 24 mV m/N. ThePMN-PT piezoelectric layer was bonded between thetwo NdFeB magnet layers using a silver-loaded epoxy Ap-plied Products E-Solder 3021 to form the ME laminatecomposite.aElectronic mail: yanminjia@yahoo.com.cnFIG. 1. Schematic diagram of NdFeB magnets/PMN-PT crystal laminatecomposite. The externally applied ac magnetic field H3 can exert the at-tractive or repellent forces on the two magnet layers simultaneously.APPLIED PHYSICS LETTERS 88, 142504 20060003-6951/2006/8814/142504/3/$23.00 © 2006 American Institute of Physics88, 142504-1The working principle of the proposed ME laminatecomposite is as follows Fig. 1. Applying an external acmagnetic field H3 along the thickness direction of the com-posite exerts the attractive or repellent forces on the twomagnet layers simultaneously. These magnetic forces thusact on the sandwiched piezoelectric layer, causing it to pro-duce piezoelectric voltages or charges. It is important tonote that this magnetic force-induced ME effect is essentiallydifferent from the magnetostrictive strain-induced ME effectused in operating traditional magnetostrictive/piezoelectriclaminate composites.3–6According to the Coulomb law of magnetostatics, themagnitude of attractive or repellant force applied on eachmagnet layer F3 isF3 = H3 · qm, 1where H3 is the externally applied ac magnetic field and qmis the magnetic pole strength of magnet layer. For a certainmagnet, qm is a constant. In our design, qm is known to be14.7 Wb. As our piezoelectric layer has been thickness po-larized, the piezoelectric constitutive equations for the layercan be expressed as10S3 = s33D T3 + g33D3, 2aE3 = − g33T3 + 33T D3, 2bwhere E3 and D3 are the electric field and electric displace-ment along the thickness direction, respectively; T3 and S3are the stress and strain along the thickness direction, respec-tively; s33D is the elastic compliance coefficient at constantelectric displacement; g33 is the piezoelectric voltage con-stant; and 33T is the dielectric impermittivity at constantstress. The stress in the piezoelectric layer T3 as a result oftransferring F3 from the top and bottom magnet layers can beexpressed asT3 =2F3A, 3where A is the interfacial area of the magnet layers and thepiezoelectric layer. Putting Eqs. 1 and 3 into Eq. 2, themagnetoelectric voltage coefficient E of the composite isobtained as follows:E =dE3dH3= − 2qmg33A. 4From Eq. 4, it is clear that E depends on qm of themagnet layers, g33 of the piezoelectric layer, and the interfa-cial area A. Substituting the corresponding material param-eters of NdFeB magnet layers and PMN-PT piezoelectriclayer into Eq. 4, E of the proposed composite is predictedto be 13.2 mV/cm Oe.Figure 2 shows the ME voltage V3 induced by an ap-plied ac magnetic field H3 of 1 Oe peak as a function oftime at the frequency of 1 kHz. Agreed with Eq. 4, V3 andH3 are of opposite phase. Besides, V3 follows steadily H3 andhas the maximum amplitude of 1.25 mV when H3 peaks at1 Oe.Figure 3 plots the induced ME voltage V3 as a functionof applied ac magnetic field H3 in the field range of10−3–10 Oe under a drive frequency of 1 kHz. It is seen thatV3 has a good linear relationship with H3 over this magneticfield range. The result also demonstrates that the compositeis very sensitive to H3 variations even at a small H3 of10−3 Oe. A higher sensitivity of 10−5–10−6 Oe could beobtained if shielding of magnetic noises could be adoptedand composite fabrication techniques could be improved.11From the slope of the plot, E is determined to be12.5 mV/cm Oe at 1 kHz. This measured E coincidesreasonably well with the predicted value of 13.2 mV/cm Oe.Nevertheless, E 12.5 mV/cm Oe of this composite issmall in comparison with that 320 mV/cm Oe at an opti-mal bias magnetic field of 500 Oe of Terfenol-D/PMN-PTlaminate composites with transverse-transverse configurationat the same frequency.3Figure 4 shows the frequency dependence of the MEvoltage coefficient E at an applied ac magnetic field H3of 1 Oe peak. It is obvious that E has a flat response inmeasured frequency range from 0.1 to 20 kHz. Owing to theinsulation of the magnet layers, not like the low-resistiveTerfenol-D alloy resistivity 0.6  m,7,8 the eddycurrent-induced thermal losses in the magnet layers are ne-glectable even the composite is exposed to a high drive fre-quency of 20 kHz. Consequently, while possessing a reducedE, the current composite can work stably for frequencies upto and, great probably, beyond 20 kHz without subject toredundant thermal-induced depolarization of its piezoelectriclayer. This permits promising applications of the compositein solid-state magnetic sensors. Another important advantageof using the composite is that no external dc bias magneticfield is needed as compared with the traditionalmagnetostrictive/piezoelectric laminate composites.3–6 ThisFIG. 2. ME voltage induced by an applied ac magnetic field of 1 Oe peak asa function of time at the frequency of 1 kHz.FIG. 3. Induced ME voltage as a function of applied ac magnetic field in thefield range of 10−3–10 Oe under a drive frequency of 1 kHz.142504-2 Jia et al. Appl. Phys. Lett. 88, 142504 2006is favorable for the miniaturization and cost saving of prac-tical devices.10 In addition, magnetic sensors based on theME effect are field sensors; they are different from searchcoils or superconducting quantum interface devicesSQUIDs, which are flux sensors. This suggests that a con-stant sensitivity may be provided as the sensor size is scaleddown, giving great potential of using this composite in mi-croelectromechanical system MEMS scale system.In summary, we have fabricated a ME laminate compos-ite by sandwiching a PMN-PT piezoelectric single crystallayer between two NdFeB magnet layers in the thicknessdirection. The experimental results have demonstrated thatthis composite possess a high E of 12.5 mV/cm Oe, a flatfrequency response from 0.1 to 20 kHz, an excellent linearrelationship between V3 and H3 in the field range of10−3–10 Oe, and a high sensitivity to small H3 of 10−3 Oe.Comparing with the conventional magnetostrictive/piezoelectric laminate composites, the current compositedoes not need any bias magnetic field, can be made muchsmaller in size, and is more effective in cost. The excellentME performance together with the inherent benefits makethis composite to be a promising and practicable ME mate-rial for magnetic sensors.The research was supported by the Natural ScienceFoundation of China 50272075, 50432030, and 50331040,Shanghai Municipal Government 05JC14079, InnovationFunds from the Shanghai Institute of Ceramics of theChinese Academy of Sciences SCX200411, the ResearchGrants Council of the HKSAR Government PolyU 5122/05E, and the Center for Smart Materials of The Hong KongPolytechnic University.1L. D. Landau and E. Lifshitz, Electrodynamics of Continuous MediaPergamon, Oxford, 1960.2V. J. Folen, G. T. Rado, and E. W. Stalder, Phys. Rev. Lett. 6, 607 1961.3S. Dong, F. Bai, J. F. Li, and D. Viehland, IEEE Trans. Ultrason. Ferro-electr. Freq. Control 51, 794 2004.4J. Ryu, A. V. Carazo, K. Uchino, and H. Kim, J. Electroceram. 7, 242001.5S. Dong, J. F. Li, and D. Viehland, Appl. Phys. Lett. 85, 5305 2004.6S. Dong, J. Y. Zhai, Z. P. Xing, J. F. Li, and D. Viehland, Appl. Phys. Lett.86, 102901 2005.7S. W. Or, T. Li, and H. L. W. Chan, J. Appl. Phys. 97, 10M308 2005.8G. Engdahl, Magnetostrictive Materials Handbook Academic, New York,2000.9H. S. Luo, G. S. Shen, P. C. Wang, X.-H. Le, and Z.-W. Yin, Int. J. Inorg.Mater. 12, 768 1997.10T. Ikeda, Fundamentals of Piezoelectricity Oxford University Press,Oxford, 1990.11S. Dong, J. F. Li, and D. Viehland, Appl. Phys. Lett. 85, 2307 2004.FIG. 4. Frequency dependence of ME voltage coefficient at an applied acmagnetic field of 1 Oe peak.142504-3 Jia et al. Appl. Phys. Lett. 88, 142504 2006

Magnetoelectric effect in laminate composite of magnets/0.7Pb(Mg[sub ⅓]Nb[sub ⅔])O₃-0.3PbTiO₃ single crystal

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