Y. K. Fetisov

Ferrite-Piezoelectric Multilayers for Magnetic Field Sensors

A magnetic field sensor based on magnetoelectric effects in a ferrite-piezoelectric layered sample is proposed. Such sensors are passive, provide direct conversion of magnetic fields into an electrical signal, and allow measurements of both ac and dc magnetic fields. A multilayer sample of nickel zinc ferrite-lead zirconate titanate has been used to characterize the sensor response to ac and dc fields, field orientations, frequency, and temperature. The sample shows a linear response for dc fields up to a maximum of 1750 Oe. The sensor output is temperature independent over 273-337 K, but is dependent on frequency of the ac excitation field. Operating at electromechanical resonance for the element enhances the sensor sensitivity by an order of magnitude. For ac magnetic field sensors, the output varies linearly with amplitude

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.

High-Sensitivity Wideband Magnetic Field Sensor Using Nonlinear Resonance Magnetoelectric Effect

A wideband ac magnetic field sensor using the nonlinear magnetoelectric effect of magnetic fields mixing in a planar structure consisting of a piezoelectric langatate and an amorphous ferromagnet has been described. The measured and pumping fields mix due to nonlinearity of the ferromagnetic layer magnetostriction. The voltage of the total frequency generated by the langatate layer is recorded at the frequency of the structure planar acoustic oscillations that provide both frequency selectivity and enhancement of the voltage by Q ≈ 1400. The maximum sensitivity of the sensor is 1.8 V/Oe, which is ~320 times higher than the sensitivity of the sensor using the linear magnetoelectric effect, but ~4 times lower than the sensitivity of the linear sensor at the resonance. The sensor operates without a dc bias magnetic field and allows registration of fields as low as ~10-5 Oe in the frequency band of 1-70 kHz with a frequency resolution of ~50 Hz.

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.

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.

Magnetic and microwave properties of nanocomposite films on the basis of Fe–Co–Ni particles of various shapes

The problem of the physical mechanisms of collective magnetic behavior, both static and dynamic, of an assembly of ferromagnetic particles comprising a nanocomposite material has been addressed. Detailed measurements of magnetization curves and microwave absorption spectra of films prepared from chemically synthesized (polyol technique) Fe–Ni–Co particles of various shapes and sizes have been performed. It has been shown that the dipole-dipole interparticle interactions play an important role in the magnetic behavior of such systems. An original method, relying on the shift of the magnetization curves in parallel and perpendicular geometry due to the planar anisotropy, allowing estimation of the concentration of magnetic particles has been proposed. The measurements of microwave absorption spectra at 9.5 GHz have revealed the features typical of local resonances localized on individual nanoparticles (Kittel mode and the lowest SWR) as well as those that can be attributed to collective behavior due to dipo...

Magnetic and microwave properties of (Ni,Co)Fe2O4-ferroelectric and (La,Ca,Sr)MnO3-ferroelectric multilayer structures

Abstract Magnetization curves and ferromagnetic resonance parameters have been measured on multilayer ferromagnetic–ferroelectric structures that show strong magnetoelectric coupling. The structures contained thick films of ferrites or substituted lanthanum manganites for the ferromagnetic phase and lead zirconate titanate for the ferroelectric phase, and were sintered at high temperatures. Results indicated defect free ferrite films with magnetic properties corresponding to their bulk ferromagnetic counterparts and deterioration of manganite film magnetic parameters due to diffusion at the interfaces.

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...