Scholarly article on topic 'Two-range magnetoelectric sensor'

Two-range magnetoelectric sensor Academic research paper on "Nano-technology"

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Academic research paper on topic "Two-range magnetoelectric sensor"

Two-range magnetoelectric sensor

M. Bichurin, V. Petrov, V. Leontyev, and A. Saplev

Citation: AIP Advances 7, 015009 (2017); doi: 10.1063/1.4973875 View online: View Table of Contents: Published by the American Institute of Physics

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Two-range magnetoelectric sensor

M. Bichurin,a V. Petrov, V. Leontyev, and A. Saplev

Institute of Electronic and Information Systems, Novgorod State University, 41 B.S.-Peterburgskaya Street, 173003 Veliky Novgorod, Russia

(Received 24 November 2016; accepted 28 December 2016; published online 5 January 2017)

In this study, we present a two-range magnetoelectric ME sensor design comprising of permendur (alloy of Fe-Co-V), nickel, and lead zirconate titanate (PZT) laminate composite. A systematic study was conducted to clarify the contribution of magnetostrictive layers variables to the ME response over the applied range of magnetic bias field. The two-range behavior was characterized by opposite sign of the ME response when magnetic dc bias is in different sub-ranges. The ME coefficient as a function of magnetic bias field was found to be dependent on the laminate composite structure. © 2017 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license ( (]

A multiferroic is a material that exhibits two or more of primary ferroic properties (ferromag-netism, ferroelectricity, ferroelasticity). A composite made of ferromagnetic and ferroelectric phases allows for coupling between the electric and magnetic order parameters and, thereby represents an engineered multiferroic. The magnetoelectric (ME) coupling in the composite is mediated by mechanical forces. Systems studied so far include ferrites, manganites, or transition metals/alloys for the ferromagnetic phase and barium titanate, polyvinylidene fluoride (PVDF), lead zirconate titanate (PZT), lead magnesium niobate-lead titanate (PMN-PT) or lead zinc niobate-lead titanate (PZN-PT) for the ferroelectric phase. There are recent reports on similar ME composites in which the ferroelectric phase is replaced by a piezoelectric such as langatate. The strain-mediated ME coupling is quite strong in several composites and has enormous potential for novel functional devices.1-4 Key advantages of the ME effect based functional devices include operation at room temperature, simple fabrication requirements, and low cost.

There have been considerable activities in recent years on ME magnetic sensors that are shown to be passive, operate at room temperature, and can be miniaturized to form an array and have performance and/or cost advantages over traditional magnetic sensing devices, including SQUID, fluxgate, Hall effect, giant magnetoresistance.5 The highest sensitivity for ME sensors are reported for composites with Metglas, a ferromagnetic alloy with high ur (required for field confinement) and high piezomagnetic coefficient. Amorphous Metglas, in general, are available as ribbons of thickness ~ 25 ^m made by rapid quenching. Ribbons of higher thickness, however, have poor magnetic parameters due to crystallization. It is therefore necessary to bond several layers of Metglas in an ME sensor to increase the effective thickness of the ferromagnetic layer in order to enhance the sensitivity. Epoxy layers of thickness 2-10 ^m used for bonding, being non-magnetic, are a potential source of demagnetizing fields.

Here we report on ME coupling in multilayers of permendur (P), an alloy with 49%Fe, 49% Co and 2% V, nickel, and PZT. We consider the 5-layer structure of P-Ni-PZT-Ni-P to avoid flexural deformations due to the structure symmetry (Fig. 1). Flexural deformations are known to decrease the ME coupling strength. The high positive piezomagnetic coefficient for permendur and high negative piezomagnetic coefficient for nickel give rise to the low-frequency ME outputs opposite in sign. The two-range behavior is characterized by opposite sign of the ME response when magnetic dc bias

aAuthor to whom correspondence should be addressed. Electronic mail: 2158-3226/2017/7(1)/015009/4 7,015009-1 © Author(s) 2017



FIG. 1. 5-layer structure of P-Ni-PZT-Ni-P.

is in different sub-ranges. The ME coefficient as a function of magnetic bias field was found to be dependent on the laminate composite structure. Details of theoretical estimates are provided here.

Next we provide a theory for the ME effect in the P-Ni-PZT-Ni-P multilayer. We consider a sample in the (1,2) plane with its thickness along the 3- direction as in Fig. 1. A bias magnetic field H and an ac field H1 are applied along the x-axis. The PZT is poled along the z-axis with an electric field E3. The sample thickness t is assumed to be much less than the width w that, in turn, is assumed to be small compared to length L. Thus, t << w << L and the only nonzero stress components are the X-components. The theoretical modeling described here is based on the equations for the strain and electric displacement of individual layers:

pSi = ps11 pTi + pd31 pE3; pD3 = pd31 pT1 + p s 33 pE3; m1 S1 = m1 s11 m1 T1 + m1 q11 m1 H1; m2 S1 = m2 sn m2 T1 + m2 qn m2 H1;

where S1 and T1 are strain and stress components, E3 and D3 are the vector components of electric field and electric displacement, s11, q11 and d31 are compliance, piezomagnetic and piezoelectric coefficients, s33 is the permittivity. The superscripts p, m1 and m2 correspond to PZT, Permendur, and nickel layers, respectively. The symmetry of piezoelectric and magnetic phase is assumed to be rc>m and cubic. For ideal mechanical coupling at the interface, the boundary conditions are as follows:

S1 = m2 S1 = pS1; pT1 ■ pt + m1 T1 ■ m11 + m2 T1

t = 0,

where pt, m1t and m2t are thicknesses of piezoelectric and two magnetostrictive components, correspondingly.

Eqs. 1 and 2 enable one to find the stress components. The output voltage induced across the piezoelectric layer can be found from open circuit condition, pD3 =0. Explicit expression for ME output voltage per unit ac magnetic field is given by

U = _ (m1 qn m1 Y11 n + m2qn m2Y11 r2)pd31 ptpY

pS33[pYn + (1 - pK^1)(nm2Yn + r2 m1 Y11)],

wherepK31 is the electromechanical coupling coefficient, r1=m1t/pt and r2=m2t/pt.

Estimated bias field dependence of induced voltage per unit ac magnetic field for P-PZT- P and Ni-PZT- Ni structures for PZT layer thickness of 1 mm is shown in Fig. 2. The material parameters used for theoretical estimates are listed below:pdn=17510-12 m/V,ps11=15.3^10-12 m2/N, s33/e0 = 1750, m1sn = 7.810-12 m2/N, m2sn=4.910-12 m2/N. Permendur and nickel plates with different thickness were used in the study. The in-plane magnetostriction A for nickel saturates at 35 ppm for H > 100 Oe and piezomagnetic coupling coefficient m2q has a maximum value of 0.440_6/Oe for H = 50 Oe.6 With increasing bias field H, one observes an increasing in-plane magnetostriction A for permendur and it saturates at 70 ppm for H > 200 Oe.7 The piezomagnetic coupling coefficientm1 q = dA1 /dH1 for Permendur is found to have a maximum value of 10"6/Oe for H =100 Oe. The data on bias

Bias field (Oe)

FIG. 2. Estimated bias field dependence of output voltage per unit ac magnetic field for P- PZT- P (1) and Ni-PZT-Ni (2) structures for PZT layer thickness of 1 mm.

field dependence of piezomagnetic coefficient for Ni from Ref. 6 and data on magnetostriction for Permendur from Ref. 7 were used to get the curves in Fig. 2.

One can see that the bias field dependence of the output voltage in Fig. 2 is different in sign for the P-PZT- P and Ni-PZT- Ni structures. This is due to positive magnetostriction for permendur and negative magnetostriction for Ni.

Using the P-Ni-PZT-Ni-P multilayer leads to the bias field dependence of ME output determined byEq. (3) (Fig. 3).

We prepared the five-layer samples by bonding a 1 cm long, 0.5 cm wide, and 1 mm thick PZT, 1 mm thick Permendur, and 1.75 mm thick Ni layers. The piezoelectric component was polarized in an electric field of 50 kV/cm. Permendur was bonded with 2 ^m thick epoxy to PZT and Ni plates. The output voltage was induced across the PZT layer and measured by an oscilloscope. The ac magnetic field of 1 Oe was produced by a Helmholtz coil driven by a signal generator. The samples were subjected to bias field H generated by electromagnet. To study the two-range behavior, we measured the ME voltage per unit ac magnetic field for frequency f = 1 kHz as a function of applied bias field. To reduce the influence of the demagnetizing effect, the in-plane ac and dc magnetic fields were applied to the sample.

Results in Fig. 3 indicate a two-range behavior that is characterized by opposite sign of the ME response when magnetic dc bias is in different sub-ranges (H<75 Oe and H>75 Oe). However, for equal thickness of permendur and nickel layers (r1=r2=1), one can see a voltage unsymmetry due to difference in magnetostrictive layers variables. The apparent unsymmetry of negative and positive peaks can be avoided by using the magnestrictive layers with different thickness. Selection of r1=1

Bias field (Oe)

FIG. 3. Estimated bias field dependence of ME output voltage per unit ac magnetic field for P-Ni-PZT-Ni-P structure for PZT layer thickness of 1 mm.

and r2=1.75 results in approximately equal negative and positive peaks in dc bias field dependence of induced voltage as in Fig. 2.

The measured values of ME voltage are shown in Fig. 2 for the P-Ni-PZT-Ni-P structure. One can see that the estimated ME voltage is in satisfactory agreement with the experimental data.

In conclusion, we demonstrate a two-range behavior of magnetostrictive-piezoelectric multilayer using permendur and nickel plates. The opposite signs of the ME response are obtained when magnetic dc bias is in different sub-ranges (H<75 Oe and H>75 Oe) for P-Ni-PZT-Ni-P structure. The apparent unsymmetry of negative and positive peaks can be avoided by using the magnestrictive layers with different thickness. We found the optimal thickness ratio for initial components and demonstrated a working prototype of the two-range sensor.

The work was supported by the Russian Science Foundation (project no. 16-12-10158).

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