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The magnetoelectric response of bi and symmetric trilayer composite structures to pulsed magnetic fields is experimentally investigated in detail. The structures comprise layers of commercially available piezoelectric (lead zirconate titanate) and magnetostrictive (permendur or nickel) materials. The magneticfield pulses have the form of a halfwave sine function with duration of 450 μs and amplitudes ranging from 500 Oe to 38 kOe. The time dependence of the resulting voltage is presented and explained by theoretical estimations. Appearance of voltage oscillations with frequencies much larger than the reciprocal pulse length is observed for sufficiently large amplitudes (∼1–10 kOe) of the magneticfield pulse. The origin of these oscillations is the excitation of bending and planar acoustic oscillations in the structures. Dependencies of the magnetoelectric voltage coefficient on the excitation frequency and the applied magnetic field are calculated by digital signal processing and compared with those obtained by the method of harmonic field modulation. The results are of interest for developing magnetoelectric sensors of pulsed magnetic fields as well as for rapid characterization of magnetoelectric composite structures.
Magnetoelectric (ME) interactions in planar composite structures comprising mechanically coupled ferromagnetic (FM) and piezoelectric (PE) layers have been investigated intensively in recent years due to the prospects of their application as sensitive magnetic field sensors [
From the literature it is clear that the behavior of ME structures in harmonic lowfrequency magnetic fields has already been intensively investigated. It was shown that the amplitude of the voltage
When the ME structure is placed into a permanent or slowly varying field
Only a few experimental studies [
The purpose of this paper is a study of the ME response of planar FMPE structures to magneticfield pulses with fixed duration in a submillisecond range. The most interesting case when the pulse amplitude exceeds the saturation field of the FM layer and various types of acoustic oscillations in the structures are excited is considered. No bias magnetic field is applied. The pulse length is sufficiently short for neglecting the charge compensation due to the finite conductivity of the PE layer. On the other hand, the magnetic pulse is much longer than the period of observed oscillations. As the object of studies the structures containing layers of commercially available cobaltiron alloy (CoFe) or nickel (Ni), possessing high magnetostriction and large enough saturation fields, and the layers of PZT ceramics, having large piezoelectric modulus, are selected. The paper starts with the description of the samples and the research methodology. Then the results of measurements together with their discussion and theoretical estimates are presented. The possibility of using the described pulsed technique for rapid characterization of ME interactions in composite structures is demonstrated. In conclusion the main findings of the work are summarized and the recommendations for the use of ME structures for the measurement of pulsed magnetic fields are given. The notation used in the paper is summarized in
Measurements were made on bi and symmetric trilayer structures, containing layers of FM metallic materials (CoFe alloy or Ni) and the piezoceramic layer of PZT: CoFe/PZT, Ni/PZT, CoFe/PZT/CoFe and Ni/PZT/Ni (see
The block diagram of the measuring apparatus is shown in
The frequency spectrum of the voltage pulse
With the increase of the amplitude of the field pulse its shape
The maximum value
Substituting the known parameters of FM and PE layers into
The oscillations of
The oscillations of
The growth of the oscillation amplitudes
To explain the origin of the modulation of generated voltage pulses, let us estimate the frequency of acoustic oscillations in the CoFe/PZT bilayer structure. The eigenfrequencies of the lowest mode for flexural (
The quality factor of bending (
Similar measurements were made for bi and trilayer structures (Ni/PZT and Ni/PZT/Ni) containing layers of ferromagnetic nickel. In this case the clipping of the generated voltage pulse (
Finally, how the results of pulse measurements can be used to rapidly characterize a ME material must be demonstrated. The measured output voltage
Indeed, the coefficient
The peculiarities of the ME response of planar composite structures with FM (CoFe alloy or Ni) and PE (PZT) layers on magneticfield pulses with a length of about 450 μs and amplitudes from 500 Oe to 38 kOe have been investigated.
It is found that when the amplitude of the field pulse exceeds the saturation field of magnetostriction in the FM layer (more than ≈ 1.5 kOe for the CoFe alloy and more than ≈ 0.5 kOe for Ni) there is a clipping of the amplitude of the generated pulse voltage. The time dependence of the generated voltage follows the time dependence of the magnetostriction in the FM material.
With further increase in pulse amplitude fields in the bilayer structures, first bending oscillations, leading to lowfrequency modulation of the voltage pulse, are excited and then the planar acoustic oscillations, leading to highfrequency modulation of the voltage pulse, appear. In symmetric trilayer structures only highfrequency planar acoustic oscillations are efficiently excited with large amplitudes of the magnetic field pulse.
It is shown that the data of pulse measurements enables one to quickly find the frequency and field dependences of the efficiency of direct ME interaction in composite structures. Note that these dependences are obtained from a single measurement as compared to two separate measurements required in the HFM method.
The results obtained can be useful for developing ME sensors of pulsed magnetic fields. To extend the working field range of these sensors FM layers with high magnetostriction saturation field strength should be selected. The appearance of the oscillations of the generated voltage due to the excitation of acoustic oscillations in the structure may lead to limitations in dynamic range of such sensors.
Financial support by the International Bureau of the German Federal Ministry of Education and Research (Project RUS 10/016) is gratefully acknowledged. The research at MIREA was supported by the Ministry of Science and Education of Russian Federation and The Russian Foundation for Basic Research. The work in Regensburg was also supported by BayStMWIVT/European Union. The manufacturers of PE and FM materials are gratefully acknowledged for providing the free samples.
Notation.
Cross sectional area of the sample  mm^{2}  
Total thickness of the sample  mm  
Thickness of the FM layer  mm  
Thickness of the PE layer  mm  
Sample width  mm  
Piezoelectric coefficient  V^{−1}·m  
Frequency of bending oscillations  Hz  
Frequency of planar oscillations  Hz  
Sampling frequency for discrete Fourier transform  Hz  

Amplitude spectrum of the voltage pulse, 
V 
V  
V  
V  

Amplitude spectrum of a rectangular pulse  Vs 

Amplitude spectrum of a halfsine pulse  Vs 

Magnetic field strength  Oe 
Magnetic field strength where 
Oe  
Saturation field of magnetostriction  Oe  
Amplitude of the magnetic pulse  Oe  

Amplitude spectrum of the magnetic pulse, 
Oe 
Electric current  A  
Cross sectional moment of inertia  m^{4}  
  
Sample length  mm  
Number of measurement points for Fourier transform    
Piezomagnetic coefficient  Oe^{−1}  
Quality factor at 
  
Quality factor at 
  
^{m} 
Compliance coefficient of the FM layer  m^{2}·N^{−1} 
^{p} 
Compliance coefficient of the PM layer  m^{2}·N^{−1} 
Generated ME voltage (see 
V  
Amplitude of voltage pulse without oscillations (see 
V  
Amplitude of voltage pulse at 
V  
Amplitude of voltage pulse at 
V  
Induced voltage in the pickup coil (see 
V  
Volume fraction of the PE phase    
Young's modulus  N·m^{−2}  
Nonlinear ME coefficient  V·Oe^{−1}·cm^{−1}  
Linear ME coefficient  V·Oe^{−1}·cm^{−1}  
ME coefficient according to [ 
V·Oe^{−1}·cm^{−1}  
Effective permittivity  A·V^{−1}·m^{−1}·s  
Magnetostriction coefficient    
Saturation magnetostriction    
Density of FM layer  kg·m^{−3}  
Density of PE layer  kg·m^{−3}  
Pulse duration  s  
Poisson's ratio    
Vacuum permeability  H·m^{−1} 
Geometry of bilayer (
Schematic diagram of the measurement setup.
The time dependence
The time dependence
Dependencies of the characteristics of the generated pulse (
Dependence of the ME interaction efficiency
Dependence of the ME coefficients
Dependence of the ME coefficients
Material parameters.
PZT  14.20  −3.7  −315  8.1    4,500 
CoFe  4.76  −1.66    8.12  60   