L. Y. Fetisov

Piezoelectric single crystal langatate and ferromagnetic composites: Studies on low-frequency and resonance magnetoelectric effects

Mechanical strain mediated magnetoelectric (ME) effects are studied in bilayers and trilayers of piezoelectric single-crystal lanthanum gallium tantalate (LGT) and magnetostrictive permendur (P). The ME voltage coefficient ranges from 2.3 V/cm Oe at 20 Hz to 720 V/cm Oe at bending resonance and is higher by an order of magnitude than in composites with ferroelectric lead zirconate titanate or lead magnesium niobate-lead titanate. The low-frequency magnetic noise for P-LGT-P is a factor of 2-10 smaller than for ferroelectrics based composites. Langatate is free of ferroelectric hysteresis, pyroelectric effects, and phase transitions up to 1450 °C and is of interest for ultrasensitive, high temperature magnetic sensors.

Resonance mixing of alternating current magnetic fields in a multiferroic composite

Theory for nonlinear mixing of harmonic magnetic fields in a ferromagnetic-ferroelectric composite structure has been developed and compared with data. In the voltage response of the composite, the model predicts a dc voltage proportional to the magnetostriction λ and its second derivative p with respect to the bias field H, an ac voltage due to linear magnetoelectric effect that is proportional to the piezomagnetic coefficient q, and a third term due to nonlinear mixing of the ac magnetic fields that is proportional to p. Doubling of the frequency and generation of voltages with sum and difference frequencies are expected due to nonlinearity of λ (H). The theoretically predicted effects are investigated in a sample of amorphous ferromagnetic film FeBSiC and a bimorph of lead zirconate titanate. Both the efficiency of frequency doubling and nonlinear mixing of the ac magnetic fields are found to be proportional to p. The effects discussed here are of interest for magnetic field sensors and signal processi...

Nonlinear resonant magnetoelectric interactions and efficient frequency doubling in a ferromagnetic-ferroelectric layered structure

Mechanical strain mediated non-linear magnetoelectric (NLME) coupling is studied in layered composites of ferromagnetic FeBSiC and piezoelectric lead zirconate titanate (PZT) bimorph. The NLME manifests as frequency doubling in the voltage response of the sample to an applied ac magnetic field. It is shown that NLME is strong (i) in the absence of DC magnetic bias, (ii) when the frequency of h is tuned to half the frequency for bending oscillations, and (iii) a PZT bimorph (instead of a single layer of PZT) is used. A model is discussed for the non-linear magnetoelectric coupling that is of interest for RF frequency doublers.

Converse magnetoelectric effects in a galfenol and lead zirconate titanate bilayer

Polycrystalline samples of galfenol Fe1−xGax (x=0.17–0.3) have been prepared and used in a bilayer with lead zirconate titanate for studies on the magnetoelectric (ME) effect. The converse ME effect which is the magnetic response of the sample to an applied ac electric field has been investigated. Piezoelectric deformations due the electric field result in an induced magnetization in galfenol that is measured as a voltage U in a pick-up coil wound on the bilayer. A resonance enhancement in the magnitude of U is evident for bending oscillations and longitudinal acoustic oscillations in the bilayer. Data on U as a function of the strength and orientation of bias field H show a maximum in ME coupling strength for in-plane component of H≈250Oe. The data have been analyzed in terms of H dependence of the magnetostriction for galfenol. The converse ME coupling is strong enough for use of the bilayer as a sensor of magnetic and electric fields.

Resonance magnetoelectric interactions in an asymmetric ferromagnetic-ferroelectric layered structure

Strain mediated magnetoelectric (ME) interactions have been investigated in a sample consisting of oppositely poled lead zirconate titanate (PZT) and asymmetric magnetostrictive layers. A thin layer of Ni with negative magnetostriction and amorphous ferromagnetic Metglas with positive magnetostriction are bonded to the PZT layers. It is shown that the magnetic layers facilitate effective excitation of bending oscillations in the structure, whereas the use of oppositely poled PZT layers results in an increase in the ME voltage at the bending resonance frequency, suppression of the voltage at the longitudinal electromechanical resonance frequency, and cancellation of thermal fluctuation in the voltage. The ME voltage coefficient at resonance is 18 V/(cm Oe); that is an order of magnitude higher than the value measured for a Ni–PZT bilayer of similar dimensions. Theoretical estimates of the ME voltage and resonance frequency are in good agreement with the data.

Influence of bias electric field on magnetoelectric interactions in ferromagnetic-piezoelectric layered structures

The nature of magnetoelectric (ME) interactions has been investigated under a dc electric field E in Ni-lead zirconante titanate bilayer for bending and acoustic modes. Both the ME voltage and the resonance frequencies are sensitively dependent on E and are attributed to variations in the permittivity and piezoelectric coefficient. A 40% increase in the ME voltage and 12% increase in the resonance frequency in comparison to zero bias were observed for bending modes. A similar behavior was observed for ME coupling at acoustic modes. The results are of interest for enhancing the sensitivity of magnetic field sensors based on ME composites.

DC magnetic field sensing based on the nonlinear magnetoelectric effect in magnetic heterostructures

Recently, highly sensitive magnetic field sensors using the magnetoelectric effect in composite ferromagnetic-piezoelectric layered structures have been demonstrated. However, most of the proposed concepts are not useful for measuring dc magnetic fields, because the conductivity of piezoelectric layers results in a strong decline of the sensors sensitivity at low frequencies. In this paper, a novel functional principle of magnetoelectric sensors for dc magnetic field measurements is described. The sensor employs the nonlinear effect of voltage harmonic generation in a composite magnetoelectric structure under the simultaneous influence of a strong imposed ac magnetic field and a weak dc magnetic field to be measured. This physical effect arises due to the nonlinear dependence of the magnetostriction in the ferromagnetic layer on the magnetic field. A sensor prototype comprising of a piezoelectric fibre transducer sandwiched between two layers of the amorphous ferromagnetic Metglas® alloy was fabricated. The specifications regarding the magnetic field range, frequency characteristics, and noise level were studied experimentally. The prototype showed the responsivity of 2.5 V mT−1 and permitted the measurement of dc magnetic fields in the range of ~10 nT to about 0.4 mT. Although sensor operation is based on the nonlinear effect, the sensor response can be made linear with respect to the measured magnetic field in a broad dynamic range extending over 5 orders of magnitude. The underlying physics is explained through a simplified theory for the proposed sensor. The functionality, differences and advantages of the magnetoelectric sensor compare well with fluxgate magnetometers. The ways to enhance the sensor performance are considered.

Resonance magnetoelectric effects in a layered composite under magnetic and electrical excitations

A novel three-layer composite consisting of a lead zirconate titanate (PZT) substrate, a PZT film on one side, and a film of ferromagnetic alloy on the other side is fabricated and used for studies on the nature of magneto-electric (ME) interactions. The strain mediated ME voltage under an ac magnetic excitation is compared with the voltage produced by pure piezoelectric response of the sample to an ac electric field. The ME voltage response measured across PZT substrate or PZT film under an ac magnetic field shows peaks at bending modes and longitudinal acoustic modes, with a higher voltage at bending mode than for the longitudinal acoustic mode. A variation in the bending mode frequency with bias magnetic field or electric field is observed and is attributed to variation in the Young’s modulus of the magnetic or piezoelectric layers. Estimates of resonance frequencies and ME coefficients are in agreement with the data. Under an ac electric excitation, piezoelectric effects result in a resonance in the v...

FREQUENCY DEPENDENCE OF MAGNETOELECTRIC VOLTAGE FOR A MULTILAYER FERRITE-PIEZOELECTRIC STRUCTURE WITH FINITE CONDUCTIVITY

ABSTRACT The frequency dependence of the magnetoelectric (ME) voltage is investigated in a thick film multilayer consisting of nickel zinc ferrite and lead zirconate titanate. A maximum in the ME voltage is observed at 1.5–2 kHz, well below the frequency for bending or acoustic modes in the sample. A model that takes into account the frequency dependence of the sample resistance and permittivity is developed. The theory is in good agreement with the data.

Magnetic Properties of Heusler-Type Microwires and Thin Films

In this paper, we studied magnetic properties of Heusler-type glass-covered microwires and thin films. The results have shown that we succeeded to prepare Ni-Mn-In thin films and Ni-Mn-Ga and Ni-Mn-In microwires that have martensitic and austenitic phases at room temperature.