Magnetoelectric magnetic field sensors
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osite magnetoelectric effect for magnetic field sensing Single-phase magnetoelectrics (MEs) have the potential to function as magnetic field sensors. However, this is impractical, as the Curie temperatures of MEs are low. Equivalently, two-phase ME composites can serve this purpose. This idea, that an artificial, top-down, ferroelectric/ferromagnetic composite would transduce a magnetic signal directly into a voltage originated at The Pennsylvania State University1 whereas natural, bottom-up ME composites were first developed at Phillips Laboratories.2–4 In such a composite, the two phases are stress-coupled, thereby producing the desired ME signal. The zero-order magnitude of the ME susceptibility, α, is given by the product rule:3 α=
∂P ∂P ∂σ ∂λ M = × × . ∂H ∂σ ∂λ M ∂H
(1)
Here, ∂λΜ/∂H describes the magnetostrictive susceptibility (i.e., the magnetostriction, λΜ, induced by the magnetic field, H); ∂σ/∂λΜ is the transduction of the magnetostrictive strain to a stress, σ, in the piezoelectric material, and the polarization change with stress, ∂P/∂σ, is the piezoelectric
effect in the piezoelectric phase. Thus, these three partial derivatives are equal to the piezomagnetic coefficient dm, the coupling coefficient kc, and the piezoelectric coefficient d, respectively. Enhancing AC susceptibility requires additional attention to the imaginary part of α (i.e., to the damping of the composite). This article reviews the various approaches used to achieve a good performance as sensitive magnetic field sensors, especially for low-frequency magnetic fields.
General properties of ME magnetic field sensors The ME effect in composite structures is mediated through an elastic interaction between the magnetostrictive and piezoelectric phases. The material is driven into excitation while two types of layers are configured in one of various operational modes, such as L–L, L–T, T–T, and c–c (where L is longitudinal, T is transverse, and c is circumferential). The ME voltage coefficient (αME) primarily depends upon the materials combination, interface quality, DC magnetic bias, and operational mode.5,6 The highest value of αME (f = 1–103 Hz) reported to date in laminated composites is ∼20 V/cm-Oe.7 As first shown in 2003,8 αME is dramatically enhanced by nearly 100× near the electromechanical resonance frequency, fr.
Dwight Viehland, Department of Materials Science and Engineering, Virginia Tech, USA; [email protected] Manfred Wuttig, University of Maryland, USA; [email protected] Jeffrey McCord, Institute for Materials Science, Kiel University, Germany; [email protected] Eckhard Quandt, Kiel University, Germany; [email protected] doi:10.1557/mrs.2018.261
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• VOLUME 43 • NOVEMBERUniversity 2018 • www.mrs.org/bulletin ©available 2018 Materials Downloaded MRS fromBULLETIN https://www.cambridge.org/core. of Winnipeg, on 25 Dec 2018 at 22:24:44, subject to the Cambridge Core terms of use, at https://www.cambridge.org/core/terms. https://doi.org/10.1557/mrs.2018.261
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Magnetoelectric magnetic field sensors
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