Scholarly article on topic 'Magnetic field-induced ferroelectric domain structure evolution and magnetoelectric coupling for [110]-oriented PMN-PT/Terfenol-D multiferroic composites'

Magnetic field-induced ferroelectric domain structure evolution and magnetoelectric coupling for [110]-oriented PMN-PT/Terfenol-D multiferroic composites Academic research paper on "Materials engineering"

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Academic research paper on topic "Magnetic field-induced ferroelectric domain structure evolution and magnetoelectric coupling for [110]-oriented PMN-PT/Terfenol-D multiferroic composites"

Magnetic field-induced ferroelectric domain structure evolution and magnetoelectric coupling for [110]-oriented PMN-PT/Terfenol-D multiferroic composites

F. Fang and W. Q. Jing

Citation: AIP Advances 6, 015008 (2016); doi: 10.1063/1.4940130 View online: http://dx.doi.Org/10.1063/1.4940130 View Table of Contents: http://aip.scitation.org/toc/adv/6Z1 Published by the American Institute of Physics

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Magnetic field-induced ferroelectric domain structure evolution and magnetoelectric coupling for [110]-oriented PMN-PT/Terfenol-D multiferroic composites

F. Fanga and W. Q. Jing

School of Aerospace, Tsinghua University, Beijing 100084, China

(Received 9 September 2015; accepted 5 January 2016; published online 13 January 2016)

Magnetic field-induced polarization rotation and magnetoelectric coupling effects are studied for [110]-oriented (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3/Tb0.3Dy0.iFe2 (PMN-xPT/Terfenol-D) multiferroic composites. Two compositions of the [110]-oriented relaxor ferroelectric single crystals, PMN-28PT and PMN-33PT, are used. In [110]-orientedPMN-28PT, domains ofrhombohedral (R) andmonoclinic (MB) phases coexist prior to the magnetic loadings. Upon the applied magnetic loadings, phase transition from monoclinic MB to R phase occurs. In [110]-oriented PMN-33PT, domains are initially of mixed orthorhombic (O) and MB phases, and the phase transition from O to MB phase takes place upon the external magnetic loading. Compared to PMN-28PT, the PMN-33PT single crystal exhibits much finer domain boundary structure prior to the magnetic loadings. Upon the magnetic loadings, more domain variants are induced via the phase transition in PMN-33PT than that in PMN-28PT single crystal. The finer domain band structure and more domain variants contribute to stronger piezoelectric activity. As aresult, the composite of PMN-33PT/Terfenol-D manifests a stronger ME coupling than PMN-28PT/Terfenol-D composite. © 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http:llcreativecommons.orgllicenseslbyl4.0i). [http://dx.doi.org/10.1063/L4940130]

I. INTRODUCTION

Multifunction and miniaturization are the key requirements for the modern electronic devices. Multiferroic materials which combine ferroelectricity, ferromagnetism, as well as the magnetoele-cric (ME) coupling are among the top candidates.1-4 Multiferroics in the form of the single phase typically possesses much lower ME effect than that of the composite form. In order to engender a strong ME coupling in the composites, piezoelectric/piezomagnetic materials with high piezoelec-tric/piezomagnetic coefficients are selected. The alloy of Terfenol-D is termed as the giant magnetostrictive material and is frequently employed as the magnetostrictive phase in the ME compos-ites.5-8 In the piezoelectric materials, single crystals of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) and Pb(Zn1 /3Nb2/3)O3-PbTiO3 (PZN-PT) attract extensive attention due to their extraordinary high piezoelectric properties.9-14 Efforts were made to reveal the ME coupling effects of the PMN-PT based multiferroic composites.5,15-19 Gao et al.16 reported giant ME coefficients with the maximum value reaching 42 V/cmOe at 10 Oe of the static magnetic bias for Metglas/PMN-PT laminates. Wang et al.11 further demonstrated that such high ME coefficients were attainable by optimizing the poling process for Metglas/PMN-PT laminates. Shen et al.18 investigated on the non-linear ME behavior in Metglas/PMN-PT/Metglas laminates and reported a maximum ME coefficient of 30 V/cm Oe under zero direct current magnetic bias. Chen et al.19 prepared laminated composites consisting of Ni43Mn41Co5Sn11 alloy and PMN-PT ferroelectric single crystal, and studied the electric field induced Hall resistivity and magnetization behaviors. As for all-thin-film ME heterostructures, Onuta et al.20,21

Corresponding author. Tel. 86-10-62113331 E-mail address: fangf@mail.tsinghua.edu.cn

2158-3226/2016/6(1 )/015008/6 6,015008-1 ~ " iilli if j "HIT \

was able to obtain a maximum ME coefficient up to 30-50 V/cmOe for Feo.7Gao.3/Pb(Zro.5Tio.48)O3 (500nm/600nm) on a silicon wafer buffered with oxide/nitride/oxide multilayers using a Pt/Ti (90-100nm/20nm) bilayer as the bottom electrode.

PMN-PT single crystals offer a rich system for multiple phase transitions. There are plenty of studies concerning the polarization rotation and phase transitions upon thermal and electric loadings for the PMN-PT single crystals.22-28 Upon the electric loading, existence of R, MA or/and MC, and T phases was identified for [001]-oriented PMN-PT single crystals,22-25 while R, MB, and O phases are revealed for [110]-oriented ones by many in situ experiments.26-28 However, investigations on the phase transition under the applied magnetic field, as well as their effects on the ME coupling are rarely reported. Recently, the authors observed the polarization rotation from R to MA for [001]-oriented PMN-28PT/Terfenol-D composite, and from O to MC and then to R for the [001]-oriented PMN-33PT/Terfenol-D composite under the applied magnetic loadings.29 The later possesses a magneto-electric coefficient (aME) up to 2 V/cmOe at a static magnetic field of 200 Oe and 1 kHz of the alternating magnetic field.29 By using piezoresponse force microscopy, Miao et al.30 reported the magnetic-field-induced ferroelectric polarization reversal in bilayer Terfenol-D/PMN-33PT composite. In this study, the ME composites are prepared by cementing together thin sheet of [110]-oriented PMN-PT single crystal and Terfenol-D plate using epoxy resin. Observations of the magnetic field-induced domain structure evolution, and measurements of ME coupling coefficient are performed simultaneously for the PMN-PT/Terfenol-D composites. The results offer basic understandings for the magneto-mechanical-electric coupling of the multiferoic composites.

II. EXPERIMENTAL PROCEDURES

When preparing the multiferroic composites, the piezomagnetic plates of Terfenol-D with a dimension of 12x10x1.5mm3 are used, which are purchased from Grirem Advanced Materials Co., Ltd., Beijing, China. At the center of the Terfenol-D plate, a through-thickness opening with a dimension of 4x4 mm2 is introduced. Single crystals of [110]-oriented PMN-28PT and PMN-33PT are provided by Shanghai Institute of Ceramics, Chinese Academy of Sciences. The single crystal plates were poled along the thickness direction and were carefully polished to a dimension of 6x5x0.1 mm3. Gold electrodes were sputtered on the top and the bottom surfaces (6x5 mm2) of the single crystal, and silver leads were attached to the electrodes with air-dry silver paste. Then, thin sheet of the PMN-PT single crystal and Terfenol-D plate are cemented together with their centers coincide with each other. The detailed experimental setup can be referred in Ref. 29.

When performing the ME measurements, a static magnetic field HS from 0 to 100 Oe is exerted on the composites using an electromagnet via a dc power supply (BOP 36-12M, KEPCO INC. NY, USA). The required ac magnetic field of 1 Oe at 1 kHz is engendered by a pair of Helmholtz coils which are connected with a digital function generator (TG1010A, ThurlbyThandar Instruments, Huntingdon, UK), and a high voltage power amplifier (PZD350A, TREK, INC. NY, USA). The applied magnetic fields, both static and alternating, are along the longitudinal direction of the sample. The induced voltage in the thickness direction is measured by a lock-in amplifier (7265, Signal Recovery, TN, USA).

When measuring the ME coefficient as a function of the applied HS, evolution of the domain structure is observed and recorded by a polarized light microscope with a video imaging system. The symmetry of domains is detected by their optical extinction angle(s). For [110]-oriented single crystals, the optical extinction angles are 0o, 35o, and 55o for the R and O phases.31 However, domains of the monoclinic phases do not follow the strict extinction angles.

III. RESULTS AND DISCUSSIONS

As shown in Fig. 1(a), for [110]-oriented PMN-28PT, prior to the magnetic loading, parallel domain bands in 50o directions are found together with some areas which show optical extinction when the polarizer is set at an angle of 35o with respect to the horizontal direction ([110]). The parallel

FIG. 1. Domain morphology change for [110]-oriented PMN-28PT single crystal (a) prior to, and (b) under a static magnetic field of 1000 Oe. The polarizer is set at 35o with respect to the horizontal direction. The applied magnetic load is in the horizontal direction. (c) Schematics for phase transition from monoclinic MB to rhombohedral R phase. Directions of the poling (P), and the applied magnetic field (H) are shown. The elongation in the applied magnetic field direction is exaggerated for clarification.

domain bands show no optical extinction whatever the angle, and one concludes that the domains belong to monoclinic lattice symmetry.

In [110]-oriented PMN-PT single crystals, existence of three types of phases, namely, R (R3m space group), MB (Cm space group), and O have been reported after poling.26-28 Based on the optical extinction angle, as well as the phase diagram for the PMN-PT solid solution system,23,32 the extinction area in Fig. 1(a) is designated as "R" phase. The regions with the parallel domain bands are labeled as "MB" with regard to the single crystals poled in [110] directions.26-28 Similar domain bands of the MB phase were previously reported by the authors.28

Upon the applied magnetic field, the Terfenol-D plate undergoes elongation along the applied magnetic field direction. Via the strain transfer, the single crystal elongates along the same direction. In-situ observation demonstrates that the region of optical extinction gradually expands. Fig. 1(b) shows the domain morphology for [110]-oriented PMN-28PT single crystal under a static magnetic field of 1000 Oe. Fig. 1(c) schematically illustrates the polarization rotation from MB to R phase for the PMN-28PT single crystal under the applied magnetic field. For the monoclinic MB phase, there are altogether 24 equivalent polarization vectors which lie along [uuv] crystallographic directions on {110} planes with u>v. However, domains tend to rotate their directions toward the applied P after electric poling. Therefore, only the polarization vectors close to the P are shown for the MB phase (Fig. 1(c)). Upon the magnetic loading, phase transition from MB to R phase occurs. The polarization vectors for the R phase are along the body diagonals as shown in Fig. 1(c), which are in accordance with the optical extinction angle of 35o with respect to the horizontal direction. The elongation in the applied magnetic field direction is exaggerated for clarification.

In PMN-33PT/Terfenol-D composite, the single crystal of PMN-33PT exhibits a much finer domain band structure than that of PMN-28PT. As shown in Fig. 2(a). Some of the areas show optical extinction on the condition that the polarizer is set 55o to the horizontal direction. These areas are

FIG. 2. Domain morphology change for [110]-oriented PMN-33PT single crystal (a) prior to, and (b) under a static magnetic field of 1000 Oe. The polarizer is set at 55o with respect to the horizontal direction. The applied magnetic load is in the horizontal direction. (c) Schematics for phase transition from orthohombic O to monoclinic MB phase. Directions of the poling (P), and the applied magnetic field (H) are shown. The elongation in the applied magnetic field direction is exaggerated for clarification.

designated as "O" phase according to the optical extinction angle, as well as the phase diagram for the PMN-PT single crystals.23,32 In other areas, domain bands in -50o direction can be seen, which resemble the domain bands structure shown in Fig. 1 and can be designated as MB phase. Upon the applied magnetic field, the extinction areas shrink and they were partly substituted by the domain bands in -50o direction, indicating the phase transition from O to MB phase. Fig. 2(c) schematically shows the polarization rotation from O to MB phase for the PMN-33PT single crystal under the applied magnetic field. Only 4 of all the 12 polarization vectors are indicated for an orthorhombic O phase due to poling, and these vectors accord with the optical extinction angle of 55o with respect to the horizontal direction (Fig. 2(a) and 2(b)). As shown in Fig. 2(c), the phase transition induces more polarization variants for the PMN-33PT single crystal, which is on the contrary with that for the PMN-28PT single crystal (Fig. 1(c)).

Fig. 3 shows the aME versus HS curves for the [110]-oriented PMN-28PT/Terfenol-D and PMN-33PT/Terfenol-D composites measured at 1 kHz of the alternating magnetic field. Both the curves show that values of aME reach a maximum at 250 Oe. Compared with the composite of PMN-28PT/Terfenol-D, PMN-33PT/Terfenol-D shows a stronger ME coupling. The maximum value of aME is 550 mV/cm Oe at Hs =250 Oe and 1 kHz of the alternating magnetic field. However, this value is much lower than the [100]-oriented counterpart, which is 2V/cm Oe.29

For composites of PMN-28PT/Terfenol-D and PMN-33PT/Terfenol-D, the different ME coupling behavior depends on the piezoelectricity of PMN-28PT and PMN-33 PT single crystals. Supposing a is the stress transfer between the Terfenol-D plate and the PMN-PT single crystal, the ME coefficient aME of the composites can be evaluated from29

dV 1 d ¿31, p<r ¿31, p da

d H Ct p d H s ■ AP d H

H (Oe)

FIG. 3. The aME versus HS curves for [110]-oriented PMN-28PT/Terfenol-D and PMN-33PT/Terfenol-D composites at 1 kHz of the applied alternating magnetic field.

Where d31,p is the piezoelectric constant of the single crystal with the induced polarization in the thickness direction upon the applied longitudinal stress. Symbols e and AP are the dielectric constant and surface area of the PMN-PT single crystal. The Equation indicates that aME is proportional to the piezoelectric voltage constant g31,p which has the formula,

d31, p

g31, p = --(2)

For single crystals of PMN-xPT with 0.26 < x < 0.34, the dielectric constant at room temperature does not change much.33 The piezoelectric behavior depends on the extent of dipole reorientation under external field. The single crystal of PMN-33PT possesses a much finer domain structure prior to the magnetic loading than that of PMN-28PT (Fig. 1(a) and 2(a)). Upon the applied magnetic loadings, phase transition from MB to R phase takes place in [110]-oriented PMN-28PT, while phase transition from O to MB phase occurs in [110]-oriented PMN-33PT. The monoclinic phase has altogether 24 polarization variants, much more than that for the R or O phases, which has 8 and 12 variants respectively. More polarization variants contribute to a higher net polarization. The finer domain band structure and the more domain variants contribute to a stronger piezoelectric activity, and higher ordering degree of dipole orientation. Consequently, a strong ME coupling is induced in Terfenol-D/PMN-33PT than that in Terfenol-D/PMN-28PT composite.

IV. CONCLUSIONS

The polarization rotation and ME coupling behavior are studied for [110]-oriented PMN-28PT/Terfenol-D and PMN-33PT/Terfenol-D multiferroic composites under the external magnetic loadings. Prior to the magnetic loadings, a mixed domain state of MB and R phases are found in the PMN-28PT single crystal, while MB and O phases coexist in the PMN-33PT single crystal. Under the applied magnetic loading, phase transition from MB to R takes place in the PMN-28PT single crystal, while that from O to MB phase occurs in PMN-33PT single crystal. ME measurements revealed that the composite of PMN-33PT/Terfenol-D shows stronger ME coupling than that of the PMN-28PT/Terfenol-D. The results indicate that the finer the domain band structure and the more the domain variants, the stronger the piezoelectric activity for the single crystal. Consequently, stronger ME coupling are induced in the PMN-33PT/Terfenol-D than that in Terfenol-D/PMN-28PT multiferroic composite.

ACKNOWLEDGEMENTS

The financial support by National Natural Science Foundation of China through Grant No. 11272174 is sincerely acknowledged. The authors also wish to give sincere thanks to Prof. H. S. Luo and Prof. X. Y. Zhao in Shanghai Institute of Ceramics, Chinese Academy of Sciences, for providing us the single crystal samples, and helpful discussions and suggestions.

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