Magnetoelectric properties of Ni/PZT/Ni layered composite for low field applications

A composite material when placed under the external magnetic/electric fields exhibits voltage/induced magnetization is known as magnetoelectric (ME) composite. Such composite materials should have ferroelectric and ferro/ferri magnetic phases as constituents. The magnetoelectric output is exhibited as a product property. Magnetoelectric composites are being used for variety of applications including resonators, filters, phase shifters, optical isolators, actuators and magnetic field sensors. Metal/ferroelectric/metal magnetoelectric composite using Ni and PZT as constituent phases has been fabricated in 2-2 composite pattern to study its product property. The paper presents magnetoelectric studies of Ni/PZT/Ni composite using low dc magnetic field magnetoelectric set-up. Using this ME set-up ME output of Ni/PZT/Ni composite is studied as a function of dc magnetic field. The results were analyzed to identify the useful magnetic field (dc and ac) range in which Ni/PZT/Ni sensor can be utilized for applications.     

Enhanced magnetoelectric coupling in Pb(Zr0.52Ti0.48)O3 film-on-CoFe2O4 bulk ceramic composite with LaNiO3 bottom electrode

By chemically depositing a conductive LaNiO₃ (LNO) electrode layer onto dense CoFe₂O₄ (CFO) ceramics, the magnetoelectric (ME) response in Pb(Zr_0.52Ti_0.48)O₃ (PZT)/CFO film-on-substrate system was significantly enhanced. Structural, morphological, ferroelectric, and piezoelectric analysis was performed for the present PZT/LNO/CFO film-electrode-substrate composites, whereby improved electric-related output was demonstrated. It was further shown that the maximum ME coefficient α _E31 could reach up to 155 mV/cm Oe, which was about 2.6 times higher than that in PZT film-on-CFO ceramics without bottom electrode layer. Further enhancement of ME response could be expected by preparing high-quality electrode layer with optimal thickness and improved fabrication processing for such film-electrode-substrate composites.     

Magnetoelectric performance of cylindrical Ni–lead zirconate titanate–Ni laminated composite synthesized by electroless deposition

The cylindrical Ni–lead zirconate titanate (PZT)–Ni laminated composites with various magnetostrictive–piezoelectric phase thickness ratios were synthesized by electroless deposition. The influences of the bias magnetic field (H _dc) and the ac magnetic field frequency (f) on magnetoelectric (ME) effect are discussed. It is seen that the ME voltage coefficient depends strongly on H _dc and f. The ME voltage coefficient and electromechanical resonance frequency increase as the magnetostrictive–piezoelectric phase thickness ratio increases. The calculated resonant frequency increases with the magnetostrictive–piezoelectric phase thickness ratio, which agrees well with the experimental results. The maximum ME voltage coefficient of the cylindrical Ni–PZT–Ni laminated composite is 3.256 V cm⁻¹ Oe⁻¹, which is much higher than that of the plate laminated composite with the same magnetostrictive–piezoelectric phase thickness ratio. Electroless deposition is an efficient method to prepare ME laminated composites with complex structures. Proper resonant frequency and stronger ME effect can be obtained by optimizing the structure.     

Dielectric and magnetoelectric properties of co-fired PbZr0.52Ti0.48O3–Co0.6Zn0.4Mn0.3Fe1.7O4–PbZr0.52Ti0.48O3 trilayer composites

In this paper we report the dielectric and magnetoelectric (ME) properties of co-fired Pb_0.52Ti_0.48O₃–Co_0.6Zn_0.4Mn_0.3Fe_1.7O₄–PbZr_0.52Ti_0.48O₃ (PZT–CZFMO–PZT) trilayer composites prepared using Mn and Zn simultaneously substituted CoFe₂O₄ (Co_0.6Zn_0.4Mn_0.3Fe_1.7O₄) as a magnetostrictive phase. For PZT–CZFMO–PZT composites, the maximum values of longitudinal and transverse ME voltage coefficient (α _E33 and α _E31 ) were observed to be comparable in magnitude contrary to the usual trend (α _E31 much greater than α _E33 ) for ME composite structures. The highest transverse ME voltage coefficient α _E31 ~64 mV/cm Oe (at an applied ac magnetic field of frequency ~1 kHz) was obtained for the composite containing the thickest layer of CZFMO. The dielectric constant spectra for PZT–CZFMO–PZT composites demonstrated very high values of resonance frequency (~47–81 MHz) and band width (~9–13 MHz).     

Influence of mechanical failure on the magnetoelectric response of magnetostrictive/piezoelectric multiferroic composite

Based on modified multi-field coupling equations, the magnetoelectric (ME) response of a new kind of Ni_47.4Mn_32.1Ga_20.5/PZT multiferroic composites are calculated by considering the mechanical failure of the brittle PZT substance. It is theoretically revealed that the Ni_47.4Mn_32.1Ga_20.5/PZT bilayer composites could produce an ideal giant ME (GME) response up to 120 V/cm Oe, much larger than the best reports up to now. However, the real ME response will be strongly limited by the mechanical strength of the brittle PZT. Reducing the PZT layer and using a mechanically stronger PZT material have been suggested to enhance the ME response.     

Hydrothermal temperature effect on magnetoelectric coupling of Ni/Pb(Zr0.52Ti0.48)O3 bilayers

Magnetoelectric (ME) Ni/Pb(Zr_0.52Ti_0.48)O₃ bilayers have been prepared by hydrothermal method. The structure and ferroelectric properties of the Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films prepared at various hydrothermal temperatures are characterized by X-ray diffraction and ferroelectric testing. With the hydrothermal temperature increasing the grain size of the PZT thin films gradually decreases leading to a gradual increase of the coercive field and a decrease of the remnant polarization of the Ni/PZT bilayers. The ME voltage coefficient of the Ni/PZT bilayers gradually decreases as hydrothermal temperature increases. The large ME coefficient makes these Ni/PZT bilayers possible for applications in multifunctional devices such as electromagnetic sensor, transducers and microwave devices.     

Magnetoelectric interaction phenomena in materials

Following the phenomenological approach of Landau and Lifshitz the existence of linear magnetoelectric effect in antiferromagnetic Cr₂O₃ was predicted by Dzyaloshinskii which was later experimentally confirmed by Astrov and Folenet al. Magnetoelectric phenomenon has been observed in several single-phase materials in which simultaneous electric and magnetic ordering coexists and in two-phase composites in which the participating phases are the ferroelectric and magnetic. The author’s group has recently undertaken a systematic study of the preparation, characterization and detection of the (ME) _H output in a few single-phase materials and two-phase composites. This article describes the magnetoelectric phenomenon in general and recent work carried out in the author’s group.     

Processing and magneto-electric properties of sol–gel-derived Pb(Zr0.52Ti0.48)O3–Ni0.8Zn0.2Fe2O4 2-2 type multilayered films

Pb(Zr_0.52Ti_0.48)O₃–Ni_0.8Zn_0.2Fe₂O₄ (PZT–NZFO) multilayered thin films with various volume fractions of the PZT phase (100, 74, 58, 48, 33, and 0%) were prepared on Pt/Ti/SiO₂/Si substrates using sol–gel spin-coating method. X-ray diffraction shows polycrystalline structure and scanning electron microscopy reveals good multilayer morphology of the composite thin film as annealed at 700 °C in air. The thickness of the composite films was estimated in the range of ~400 to ~600 nm. The ferroelectric and magnetic properties were measured as function of the volume fractions of the PZT phase. The magnetoelectric (ME) effect was investigated under various bias magnetic fields. The maximum ME voltage coefficient (α _E  = dE/dH) is 278 mV/cmOe for the composite film with the volume fractions of the PZT phase of ~48%.     

Effect of interface bonding on the phase-transformation-aided magnetoelectric effect in ferromagnetic/ferroelectric composites

Based on modified constitutive equations and finite element method, calculations have been performed to study the effect of interface bonding on the phase-transition-aided magnetoelectric (ME) response in a new kind of NiMnGa/lead–zirconate–titanate (PZT) multiferroic laminate composites. The results quantitatively show that the ME effect is remarkably dependent on both the interface layer characteristics and the interface layer thickness. Stiffer and thinner interface layers are apt to produce higher ME effect. Calculations are in good agreement with available experimental results. Furthermore, the theoretical approach was improved to consider the enhancement in the magnetostriction of martensites induced by pre-applied opposing stress. Predictions reveal that the usage of single crystal Fe₇Pd₃ as ferromagnetic phase to form magnetoelectric composite with PZT can produce a high ME up to ~1 V/cm Oe.     

Studies on magnetic and magnetoelectric properties of the NiFe2O4–Ba0.7Sr0.3TiO3 composites

The magnetic and magnetoelectric properties of magnetoelectric (ME) composites consisting of with nickel ferrite (NiFe₂O₄) and barium strontium titanate (Ba_0.7Sr_0.3TiO₃) were investigated. The composites were prepared by standard double sintering ceramic method. The X-ray diffraction analysis was carried out to confirm the phases formed during sintering and also to calculate the lattice parameters. The hysteresis measurements were done to determine saturation magnetization (M_s), remenance magnetization (M_r) and coercivity (H_c) of the samples. The magnetoelectric voltage coefficient (dE/dH)_H was studied as a function of intensity of the magnetic field. The measured magnetoelectric (ME) response demonstrated strong dependence on the volume fraction of NiFe₂O₄ and the applied magnetic field. A large ME voltage coefficient of about 560 μVcm⁻¹Oe⁻¹ was observed for 15% NiFe₂O₄ + 85% Ba_0.7Sr_0.3TiO₃ composite.     

Magnetoelectric and electrical properties of WO3-doped (Ni0.8Zn0.1Cu0.1)Fe2O4/[Pb(Ni1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3–PbTiO3] composites

A total of 5 mol% WO₃-doped (1−x)(Ni_0.8Zn_0.1Cu_0.1)Fe₂O₄/xPb(Ni_1/3Nb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃–PbTiO₃ ((1−x)NZCF/xPNN-PZN-PT) magnetoelectric particulate ceramic composites were prepared by conventional solid-state reaction method via low-temperature sintering process. X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM) observation indicate that piezoelectric phase and ferrite phase coexist in the sintered particulate ceramic composites. Dielectric property of the (1−x)NZCF/x0.53PNN–0.02PZN–0.05Pb(Ni_1/2W_1/2)O₃–0.40PT ((1−x)NZCF/xPNN-PZN-PNW-PT, nominal composition) composites is improved greatly as compared to that of the undoped (1−x)NZCF/xPNN-PZN-PT composites. The WO₃-doped (1−x)NZCF/xPNN-PZN-PT composites exhibit typical P–E hysteresis loops at room temperature accompanied by the decrease of saturation polarization (P _s) and remnant polarization (P _r). At the same time, piezoelectric property of the composites deteriorates greatly with the increase of ferrite content. The (1−x)NZCF/xPNN-PZN-PNW-PT composites can be electrically and magnetically poled and exhibit apparent magnetoelectric (ME) effect. A maximum ME voltage coefficient of 13.1 mV/(cm Oe) is obtained in the 0.1NZCF/0.9PNN-PZN-PNW-PT composite at 400 Oe d.c. magnetic bias field superimposed 1 kHz a.c. magnetic field with 5 Oe amplitude. The addition of WO₃ in the piezoelectric phase decreases sintering temperature greatly from 1180 °C to 950 °C and decreases dielectric loss sharply of the composites, thus the ME voltage coefficient increases. Such ceramic processing is valuable for the preparation of magnetoelectric particulate ceramic composites with excellent ME effect.     

Effect of heat treatment on the properties of Metglas foils, and laminated magnetoelectric composites made thereof

Annealing of magnetostrictive Metglas foils, subsequently incorporated into laminated Metglas/Pb(Zr, Ti)O₃ magnetoelectric (ME) composites, is shown to result in improved magnetic properties, as well as ME coefficients. Annealing of the foils at 350 °C resulted in partial crystallization, without oxidation or magnetic cluster formation that would reduce the magnetization. Laminate composites made with these annealed Metglas foils had improved ME coefficients.     

用于磁传感器的新结构磁电复合材料

研究了可用于磁场传感器的磁电复合材料, 对传统的磁电复合材料进行了结构创新, 采用条状PZT和 Terfenol-D 的材料体系, 用热固树脂进行粘合, Terfenol-D 沿长度方向磁化且PZT条沿厚度方向极化。与传统的1-3型复合不同的是: 每根PZT的输出极被串联起来。在同样的磁场激励下, 新型复合材料的输出电压为相同体积的同种结构复合材料的2.2倍, 增强了材料对磁场的灵敏度和抗噪声性能。      

An experimental setup for dynamic measurement of magnetoelectric effect

An experimental setup is developed for the measurement of dynamic magnetoelectric effect (ME) in polycrystalline materials, using a time varying DC magnetic field on which an AC magnetic field is superimposed. The experimental data on ME on Bi₅FeTi₃O₁₅ and a solid solution of (90%)BiFeO₃-(10%)BaTiO₃ are obtained using this setup. The linear and higher order ME coefficients can be evaluated from the output voltage. The temperature variation of ME data gives additional information corroborating with the data on magnetization.     

Magnetoelectric properties of CoFe2O4–Pb(Zr0.52Ti0.48)O3 multilayered composite film via sol–gel method

CoFe₂O₄–Pb(Zr_0.52Ti_0.48)O₃ (CFO–PZT) multilayered composite film was prepared on Pt/Ti/SiO₂/Si substrate via a sol–gel method and spin-coating technique. Results show that PZT and CFO phases exist in the composite film, calcined at 700 °C, besides substrate phase, and no obvious impurity phases can be detected. The composite film exhibits layered structure with obvious boundary between CFO and PZT films. Ferroelectric and ferromagnetic properties were simultaneously observed in the composite film, evidencing the ferroelectric and ferromagnetic properties in the composite film. The composite film exhibits both good magnetic and electric properties, as well as, magnetoelectric (ME) effect. The saturation magnetization value of the composite film is lower than that of the pure CFO film derived by the same processing as a result of the effect of the nonferromagnetic PZT layers. Ferroelectric hysteresis loops reveal that saturated polarization and remanent polarization of the composite film are lower than those of the pure PZT films. The composite film exhibits a very large ME effect, which makes the composite film attractive for technological applications as devices.     

Dielectric and magnetoelectric properties of (x)Ni0.8Co0.1Cu0.1Fe2O4/(1 − x)PbZr0.8Ti0.2O3 composites

Ceramic composites of Ni_0.8Co_0.1Cu_0.1Fe₂O₄ and lead–zirconate–titanate (PZT) were prepared using conventional solid state reaction method. The presence of constituent phases in composites was confirmed by X-ray diffraction (XRD). The variation of dielectric constant with frequency (100 Hz–1 MHz) and temperature has been studied. The variation of loss tangent (tan δ) with temperature (at frequency 1 kHz) has also been studied. The magnetoelectric (ME) output was measured as a function of dc magnetic field. The maximum value of ME output (625 mV/cm) was observed for 25% ferrite + 75% ferroelectric phase. The maximum ME response can be explained in terms of the content of ferrite, permittivity of dielectric material and the intensity of magnetic field. The ME response of these composites was observed to be linear within low dc magnetic field. These composites may form the basis for the development of magnetic sensors and transducers for use in solid state microelectronics and microwave devices.     

Magnetoelectric effect of the multilayered CoFe2O4/BaTiO3 composites fabricated by tape casting

This paper presents the structural, ferroelectric, ferromagnetic, resonance and magnetoelectric (ME) properties of multilayered ME composites fabricated using tape casting method. The compositions corresponding to CoFe₂O₄ (CFO) with particle size of ~150?nm and BaTiO₃ (BTO) with particle size of ~100?nm were chosen as ferromagnetic and ferroelectric phases, respectively. Delamination was found at the interface between CFO and BTO layers, which was related to the residual stress due to the difference in thermal expansion coefficient between the two layers. The largest direct magnetoelectric and converse magnetoelectric coefficients of the multilayered ME composite were, respectively, 36?μV/cm?Oe at a bias magnetic field of 2,800?Oe and 1.16?×?10^?3?G/V at a frequency of 30?kHz. In addition, the corresponding interfacial coupling coefficient was calculated to be 3.2?×?10^?5. For the multilayered ME composite, a resonance frequency of 4.96?MHz and a bandwidth of 40?kHz were obtained using capacitance-frequency spectrum method.     

Magnetoelectricity in polyurethane films loaded with different magnetic particles

Particulate polymer composites consisting of Terfenol-D/Polyurethane, Fe₃O₄/Polyurethane, Nickel/Polyurethane and particulate composite layers were prepared by using a simple solution cast method. Magnetoelectric (ME) effect is characterized by measuring the amplitude of the magnetoelectric current versus different input parameters that appear in the theoretical current expression. The results yield two conclusions: 1.Whatever the filler type (Terfenol-D, Fe₃O₄ or Nickel), the microcomposites show a magnetoelectric effect. 2. The magnetostrictive property of the material does not have a direct influence on the ME effect since ME sensitivity is dc field independent and the magnetoelectric coefficient α_p has close values in ac field for all types of polymer fillers.     

Conductivity, dielectric behaviour and magnetoelectric effect in copper ferrite-barium titanate composites

Composites of CuFe₂O₄ and BaTiO₃ were prepared using a conventional ceramic double sintering process. The presence of both phases was confirmed by X-ray diffraction. The variations of resistivity and thermo emf with temperature in these samples were studied. All the composites showed n-type behaviour. The variation of dielectric constant (έ′) in the frequency range 100 Hz to 1 MHz and with temperature at constant frequency were studied. The conduction phenomenon was explained on the basis of a small polaron-hopping model. Also confirmation of this phenomenon was made with the help of a.c. conductivity measurements. The static value of the magnetoelectric conversion factor, i.e. d.c. (ME)_H was studied as a function of intensity of the magnetic field. The maximum value of ME coefficient was observed for 75% ferroelectric phase composite.     

Exchange biasing of magnetoelectric composites

Magnetoelectric composite materials are promising candidates for highly sensitive magnetic-field sensors. However, the composites showing the highest reported magnetoelectric coefficients require the presence of external d.c. magnetic bias fields, which is detrimental to their use as sensitive high-resolution magnetic-field sensors. Here, we report magnetoelectric composite materials that instead rely on intrinsic magnetic fields arising from exchange bias in the device. Thin-film magnetoelectric two-two composites were fabricated by magnetron sputtering on silicon-cantilever substrates. The composites consist of piezoelectric AlN and multilayers with the sequence Ta/Cu/Mn(70)Ir(30)/Fe(50)Co(50) or Ta/Cu/Mn(70)Ir(30)/Fe(70.2)Co(7.8)Si(12)B(10) serving as the magnetostrictive component. The thickness of the ferromagnetic layers and angle dependency of the exchange bias field are used to adjust the shift of the magnetostriction curve in such a way that the maximum piezomagnetic coefficient occurs at zero magnetic bias field. These self-biased composites show high sensitivity to a.c. magnetic fields with a maximum magnetoelectric coefficient of 96 V cm(-1) Oe(-1) at mechanical resonance.