Magnetoelectric Voltage Coefficient αE Research Articles

Giant magnetoelectric effects in serial-parallel connected Metglas/PZT arrays with magnetostrictively homogeneous laminates

Abstract To ensure the magnetostrictive softness, the homogeneity, the decrease of the shear-lag effect and the space-saving construction of narrowed longitudinal-transverse L-T magnetoelectric (ME) composites, a novel parallel-connected-multi-bars (PCMB) geometry of PZT/Metglas is proposed and investigated by simulation and experiment. In this case, Metglas layers are structured in different geometries from the conventional single bar (c-SB) to conventional separated multiple bars (c-SMB), elongated separate multi-bar (e-SMB) and n-magnetic-bar based PCMB (n-PCMB). This n-PCMB geometry divides the conventional ME configuration into n parallel-connected ME units (n-PCMEU) according to the magnetic geometries. The optimal ME performance with the largest ME voltage coefficient αE of 630 V/cm.Oe is achieved in PCMEU with two Metglas bars (n = 2). The ME voltage coefficient can be further enhanced by integrating m of these optimal PCMEUs in series to form a serial-parallel ME unit array m-S (n-PMEU)A. The αE value increases by a factor of 3.6 and reaches 2.238 kV/cm.Oe for 4-S (2-PMEU)A, a factor that is almost equal to m. The resulting 4-S (2-PMEU)A sensor possesses an extremely high sensitivity of 18.1 μV/nT, with a resolution of 10−1 nT.

Integration of c-axis oriented Bi3.15Nd0.85Ti2.95Hf0.05O12/La0.67Sr0.33MnO3 ferromagnetic-ferroelectric composite film on Si substrate

A La0.67Sr0.33MnO3 (LSMO) ferromagnetic layer and a Nd3+/Hf4+ co-substituted Bi4Ti3O12 (Bi3.15Nd0.85Ti3-xHfxO12 (BNTHx, x = 0, 0.025, 0.05, 0.1 and 0.15)) ferroelectric layer were successively deposited onto the (00 l)-oriented LaNiO3 (LNO) layer buffered (001) Si substrate via all chemical solution deposition (CSD) method. As a result, the BNTHx/LSMO ferromagnetic-ferroelectric composite films integrated on Si substrate exhibit high c-axis orientation. The Nd3+/Hf4+ co-substituted BNTHx films have the lower leakage current and the better ferroelectric properties than the mono-substituted Bi4Ti3O12 (Bi3.15Nd0.85Ti3O12 and Bi4Ti2.95Hf0.05O12) films. In particular, the BNTH0.05/LSMO/LNO film has the lowest leakage current density of 2.5 × 10−7 A/cm2 at 200 kV/cm, and the highest remnant polarization (Pr) of 27.3 μC/cm2. The BNTH0.05/LSMO/LNO composite film also exhibits the soft ferromagnetism characteristics with a high saturated magnetization of 258 emu/cm3 at 300 K, and the excellent magnetoelectric (ME) effect. The variations of ME voltage coefficient αE values with DC bias magnetic field Hbias shows that the BNTH0.05/LSMO/LNO film has the high αE value at near zero Hbias. Moreover, at Hbias = 0 Oe, the αE value gradually increases from zero with the increasing of the AC magnetic field frequency, and eventually reaches about 18.9 V/cm·Oe at 100 kHz, suggesting the existence of self-biased ME effect.

Ferromagnetic, ferroelectric and magnetoelectric properties of (001)-oriented Pb(Zr0.52Ti0.48)O3/La0.67Sr0.33MnO3 composite films deposited on Si substrates using chemical solution deposition

Using (001)-oriented LaNiO3 (LNO) as a buffer layer, the ferromagnetic-ferroelectric layered composite film of Pb(Zr0.52Ti0.48)O3/La0.67Sr0.33MnO3 (PZT/LSMO) with a (001) orientation was deposited on a Si (100) substrate through a chemical solution deposition (CSD) method. The LNO buffer layer promotes the (001) preferential orientation and the columnar growth of the overlying LSMO and PZT layers. The oriented PZT/LSMO/LNO film has soft ferromagnetism characteristics, and a higher saturated magnetization (750.9 emu/cm3) compared with the non-oriented one. The effects of the orientation and the selection of the bottom electrode (BE) on ferroelectric properties of PZT/LSMO/LNO composite films were investigated. Using LNO as the BE, the oriented PZT/LSMO/LNO film exhibits the highest remnant polarization (Pr) of 30.0 μC/cm2 and the lowest leakage current density of 10−6 A/cm2 at 300 kV/cm. The oriented PZT/LSMO/LNO film also exhibits a good magnetoelectric (ME) effect and shows the maximum ME voltage coefficient αE of 125.9 mV/cm·Oe at room temperature. Our investigation provides an effective way to replace the expensive single-crystal substrates, and to promote the application of ferromagnetic-ferroelectric composite films into the Si-based microelectronic field.

Giant magnetoelectric effect in negative magnetostrictive/piezoelectric/positive magnetostrictive semiring structure

Magnetoelectric (ME) Ni/PZT/TbFe2 and TbFe2/PZT composites with two semiring structures are prepared. The dependence between ME coupling and magnetostrictive property of the composite is discussed. Because Ni possesses negative magnetostrictive property and TbFe2 shows positive magnetostrictive property, the ME voltage coefficient of Ni/PZT/TbFe2 semiring structure is much larger than that of TbFe2/PZT. In these composites, the ME voltage coefficient increases and the resonance frequency gradually decreases with the increase of the semiring radius, showing that structural parameters are key factors to the composite properties. Due to the strong ME coupling effect, a giant ME voltage coefficient αE = 44.8 V cm−1 Oe−1 is obtained. This approach opens a way for the design of ME composites with giant ME voltage coefficient.

Evolution of the charge- and strain-mediated magnetoelectric coupling effect in the La0.7Sr0.3MnO3/BaTiO3 bilayer

The epitaxial La0.7Sr0.3MnO3/BaTiO3 (LSMO/BTO) bilayer films with various volume fraction ν of ferroelectric (FE) phase (BTO) are fabricated on (001) oriented LaAlO3 substrate. The value of ν is regulated by changing the thickness of LSMO film, and fixing the thickness of BTO film. The value of ν is demonstrated to play a key role in determining the interface magnetoelectric (ME) coupling coefficient (k) of the LSMO/BTO bilayers, i.e. a lower value of ν leads to a lower value of k. Furthermore, as ν is 0.91, experimental value of the ME voltage coefficient αE is higher than its calculated value, which indicates that the main ME coupling mechanism have evolved from strain-mediated to charge-mediated. This result can provide an available method for the design of multiferroic composite bilayer films with adjustable ME coupling mechanism by optimizing the volume fraction of FE phase.

Zero-biased and resonant magnetoelectric effect in magnetostrictive/piezoelectric multilayered composites

Magnetoelectric (ME) effect was investigated in various multilayered composites with various magnetostrictive materials Ni, FeNi and FeCo prepared by electroless deposition. Compared with the homogeneous ME composites, Ni/PZT/Ni and FeCo/PZT/FeCo, the ME voltage coefficient αE,31 of graded ME composites with two different magnetostrictive materials exhibit significant hysteresis phenomenon as a function of the external dc magnetic field at low frequency. The zero-biased ME response has been observed and can be attributed to a built-in magnetic field. However, at longitudinal vibration mode the ME voltage coefficient has been weakened in graded ME composites. The zero bias ME coupling observed in composites with graded magnetostrictive materials can be used in magnetic sensors with high sensitivity.

Interface Effects on the Magnetoelectric Properties of Magnetoelectric Multilayer Composites

The magnetoelectric (ME) effect is studied in the terfenol-D/Pb(Zr, Ti)O3 (PZT) multilayer composites prepared by silver epoxy. A theoretical model reveals that the ME voltage coefficient αE,31 is a constant when the total thickness of the multilayer composites is the same. However, the interface defects exist in multilayer composites in experiments and the interface energy loss increases with increasing the stacking periodicity, which leads to the gradual decrease of the ME voltage coefficient αE,31. The resonant frequency of terfenol-D/PZT multilayer composites is independent of the stacking periodicity and agrees well with the predicted one. One can achieve a strong ME coupling by improving the interface conditions to meet the needs for practical applications.

Magnetocapacitance and structure properties of Bi0.85−xLa0.15PbxFeO3 ceramics

To study the effects of La and Pb co-doping on the magnetocapacitance (MC) and structure properties of BiFeO3, single-phase Bi0.85–xLa0.15PbxFeO3 (BLPF, x=0–0.10) multiferroic ceramics were prepared by a solid-state reaction. In the Rietveld refinement, good agreement between the observed and calculated pattern was observed. The dielectric response of these samples was analyzed in the frequency range of 100Hz–10MHz, and it was found that Pb-doping drastically improved the dielectric properties. Moreover, the MC and magnetoelectric effect were enhanced, show a large MC effect (~18.8%) and magnetoelectric voltage coefficient αE (~90.6mV/cm/Oe) for BLPFx=0.05 ceramic.

Strong magnetoelectric coupling in sol–gel derived multiferroic (Pb0.76Ca0.24)TiO3–CoFe2O4 composite films

A multilayer heterostructure composite thin films consisting of alternating layers (Pb0.76Ca0.24)TiO3 (PCT) and CoFe2O4 (CFO) were grown on Pt/Ti/SiO2/Si(100) substrate by a sol–gel process. X-ray measurements indicated high quality of crystallization of both PCT and CFO layers. The magnetic and ferroelectric properties of the composite were investigated. Well-defined polarization vs. electric field (P–E) and magnetic hysteresis (M-H) loops were obtained. A strong magnetoelectric (ME) response was observed in the sample which was subjected to an alternating magnetic field, and a high ME voltage coefficient αE = 870 mV/Oe cm was obtained for the composite thin films when applied magnetic field parallel to the sample plane.

Giant magnetoelectric effects in multilayered composites of cobalt ferrite and lead magnesium niobate titanate

The magnetoelectric (ME) coupling responses of [CoFe2O4/(1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3]n, represented as (CFO/PMNT)n, multilayered composites were theoretically investigated by using an average method. It is found that a stronger interface coupling could be obtained in multilayers than in bilayers if the number of layers (n) is reasonably increased. Using an empirical dependence of the interface coupling parameter on the number of layers n, it is theoretically estimated that the ME coupling effect is first enhanced and then deteriorated with the gradual increase in n. The best ME response is estimated to occur at n=15, where the transverse ME voltage coefficient αE,31 reaches as high as 658 mV·cm−1·Oe−1. Moreover, it is theoretically found that the ME coupling effect in (CFO/PMNT)n multilayered composites is strongly dependent on the volume fraction of the piezoelectric (or magnetostrictive) phase, and the ME voltage coefficient for transverse field orientation (αE,31) is estimated to be roughly 90% higher than that for the longitudinal case (αE,33), revealing a large anisotropy in the ME coupling effect of (CFO/PMNT)n multilayered composites. These findings pave the way for experimental achievement of strong ME coupling responses, and provide important implications for the design and performance optimization of related devices comprising this kind of multiferroic magnetoelectric materials.

Enhanced magnetoelectric effect in longitudinal-transverse mode Terfenol-D∕Pb(Mg1∕3Nb2∕3)O3–PbTiO3 laminate composites with optimal crystal cut

Magnetoelectric (ME) laminate composite consisting of optimal crystal cut thickness-polarized piezoelectric 0.7Pb(Mg1∕3Nb2∕3)O3–0.3PbTiO3 (PMN-PT) single crystal and the length-magnetized magnetostrictive Tb0.3Dy0.7Fe1.92 (Terfenol-D) alloy has been fabricated. The cut optimization of PMN-PT crystal greatly enhances the longitudinally magnetized-transversely polarized (L-T) mode ME effect, which has a superior ME voltage coefficient αE of ∼3.02V∕cmOe in low frequency band. Near the resonance frequency of 95kHz, the coefficient dramatically increases and reaches the maximized value of 33.2V∕cmOe, which is almost two times larger than the previously reported ⟨001⟩-oriented PMN-PT crystal based L-T mode laminate composite.

Frequency and field dependence of magnetoelectric interactions in layered ferromagnetic transition metal-piezoelectric lead zirconate titanate

The strength of magnetoelectric (ME) coupling at 10Hz–3MHz has been measured in trilayers of Fe, Co, or Ni and lead zirconate titanate (PZT). The strongest ME coupling is measured for trilayers with Ni and the weakest in Co. Data on ME voltage coefficient αE versus bias magnetic field H for Fe–PZT–Fe show unique features including zero crossing and sign reversal. Measurements of frequency dependence of αE reveal a giant ME coupling due to the electromechanical resonance at 200–300kHz for radial modes and at ∼2.7MHz for thickness modes. Theoretical estimates of field and frequency dependence of αE are in very good agreement with the data.