Magnetoelectric Coefficient αME Research Articles

Simultaneously enhanced ferroelectric and magnetic properties of SrTiO3‐modified Bi0.88Sm0.12FeO3 ceramics

AbstractIn the present study, SrTiO3 was selected to enhance the multiferroic characteristics of Bi0.88Sm0.12FeO3 (BSF) ceramics. With increasing SrTiO3 content, the principal phase of BSF ceramic transitions from rhombohedral R3c to Pna21. Through DSC and dielectric analysis, it was observed that both the Curie temperature and Néel temperature decreased proportionally with the augmentation of SrTiO3 content. When x = .1, the optimal ferroelectric performance is achieved, and the highest remanent polarization value is 55.47 µC/cm2, significantly surpassing that of BSF ceramics. Moreover, the PFM test results showed that as the substitution content increased, the domains in the BSF ceramic gradually transformed from normal ferroelectric domains to polar nanomicro‐domains. Magnetic and magnetoelectric results show that when x = .1, the best magnetic properties are obtained, Mr = 59.7 emu/mol. The magnetoelectric coefficient αME initially increased and then decreased with the increasing SrTiO3 content, reaching its optimum magnetoelectric properties at x = .1, where αME = .47 mV cm–1 Oe–1. In summary, when the substitution amount of SrTiO3 reaches 10%, the ferroelectric, magnetic, and magnetoelectric properties of BSF ceramics are significantly improved.

A Spin-Charge-Regulated Self-Powered Nanogenerator for Simultaneous Pyro-Magneto-Electric Energy Harvesting.

In view of the depletion of natural energy resources, harvesting energy from waste is a revolution to simultaneously capture, unite, and recycle various types of waste energies in flexible devices. Thus, in this work, a spin-charge-regulated pyro-magneto-electric nanogenerator is devised at a well-known ferroelectric P(VDF-TrFE) copolymer. It promptly stores thermal-magnetic energies in a "capacitor" that generates electricity at room temperature. The ferroelectric domains are regulated to slip at the interfaces (also twins) of duly promoting polarization and other properties. An excellent pyroelectric coefficient p ∼ 615 nC·m-2·K-1 is obtained, with duly enhanced stimuli of a thermal sensitivity ∼1.05 V·K-1, a magnetoelectric coefficient αme ∼8.8 mV·cm-1·Oe-1 at 180 Hz (resonance frequency), and a magnetosensitivity ∼473 V/T. It is noteworthy that a strategy of further improving p (up to 41.2 μC·m-2·K-1) and αme (up to 23.6 mV·cm-1·Oe-1) is realized in the electrically poled dipoles. In a model hybrid structure, the spins lead to switch up the electric dipoles parallel at the polymer chains in a cohesive charged layer. It is an innovative approach for efficiently scavenging waste energies from electric vehicles, homes, and industries, where abundant thermal and magnetic energies are accessible. This sustainable strategy could be useful in next-generation self-powered electronics.

Magneto-Mechano-Electric generator of lead-free piezoelectric Ba0.95Ca0.05Ti0.95Zr0.025Sn0.025O3 / Co0.8Ni0.2Fe2O4 magnetostrictive multiferroic laminate structure

We report the magneto-mechano-electric (MME) response of (2–2) layered magnetostrictive-piezoelectric composite structures of Co0.8Ni0.2Fe2O4 / Ba0.95Ca0.05Ti0.95Zr0.025Sn0.025O3 / Co0.8Ni0.2Fe2O4 (CNFO/BCTZS/CNFO) ceramics. The basic magnetic and electric properties to support the multiferroism nature were studied and discussed. The BCTZS piezoceramics showed a piezoelectric charge coefficient of (d33) ∼ 149 pC/N, piezoelectric voltage coefficient of (g33) ∼ 7.64 × 10-3 (Vm/N) and planar electromechanical coupling factor of (kp) ∼ 26 % with additional benefits of phase coexistence of orthorhombic-tetragonal lattice symmetries near room temperature. The CNFO magnetostrictive phase reveals a piezomagnetic coefficient (q11 = dλ11/dH) of − 0.0625 ppm/Oe at a lower magnetic field bias of 600 Oe. The MME response of CNFO/BCTZS/CNFO multiferroics is validated by measuring the magnetoelectric (ME) coefficient αME in longitudinal–transverse (L-T) mode. The CNFO/BCTZS/CNFO structure revealed the αME of 50.8 mV/cm·Oe at a field of 644 Oe at off-resonance frequency i.e. 1 kHz. The frequency-dependent αME measurements at two different constants (Hdc), i.e. 100 Oe and 600 Oe showed the resonant enhancement in ME coupling at 8.5 kHz by attaining the peak value of magnetoelectric coefficient αME ∼ 0.27 V/cm·Oe and 0.107 V/cm·Oe respectively. Consequently, it is confirmed that due to the electromechanical resonance effect, the magnitude of αME is increased by six times as that measured at off-resonance i.e. 1 kHz. Therefore, the present multiferroic 2–2 structures are suitable for magneto-mechano-electric (MME) energy harvesters as well as magnetic field sensor applications.

Structure evidence of Pna21 phase and field-induced transition of Pna21/R3c in Bi1−xSmxFe0.99Ti0.01O3 ceramics

In this study, the structure evidence of the Pna21 phase and the field-induced transition of Pna21/R3c have been quantitatively investigated in Bi1-xSmxFe0.99Ti0.01O3 (x = 0.12, 0.14, and 0.16) ceramics together with the subsequent electric field-controlled magnetism. A sequential phase transition of R3c-Pna21-Pbnm is detected by Rietveld refinement of the x-ray diffraction data. Further, the electric field-induced phase transition is investigated near the morphotropic phase boundary at x = 0.14, where the structure is tuned from Pna21 to R3c with poling treatment, and this transition could become reversible with as-annealing after poling. For x = 0.14, the structure is tuned from Pna21 to R3c with poling treatment, and this transition could become reversible with as-annealing after poling. The phase transition is confirmed by Rietveld refinements together with VSM measurements, providing an opportunity for electric field-controlled magnetism. The magnetoelectric coupling is enhanced, and the linear magnetoelectric coefficient αME up to 0.91 mV/Oe·cm is obtained in Bi1-xSmxFe0.99Ti0.01O3 ceramics. More importantly, the R3c and Pna21 structures are confirmed by selected area electron diffraction and dark-field analysis at x = 0.14, and the high-resolution TEM image demonstrates the coexistence of the R3c and Pna21 structures.

Enhanced multiferroic characteristics in hexagonal ScMn1−xFexO3 ceramics

In the present study, enhanced antiferromagnetic characteristics and room temperature magnetoelectric coupling are achieved by Fe-substitution for Mn in h-ScMnO3. The antiferromagnetic Néel temperature (TN) increases from 131 K for ScMnO3 up to 140 K for ScMn0.8Fe0.2O3. Electric field controlled magnetism is confirmed for ScMn0.8Fe0.2O3 at room temperature, combining with the short-range magnetic spin ordering. The Rietveld structural refinement and selected area electron diffraction confirm the noncentrosymmetric P63cm structure for the present ceramics. The ferroelectric domain walls at the atomic scale are determined by the aberration-corrected high-angle annular dark-field scanning transmission electron microscopy; meanwhile, the spontaneous polarization of 5.6 μC/cm2 is determined. The noticeable magnetoelectric coefficient αME ∼ 0.78 mV/cm Oe (measured under a magnetic field up to 3000 Oe) is obtained in ScMn0.8Fe0.2O3, which is quite stable with the applied magnetic field, reflecting coupling of the short-range spin ordering with the ferroelectric ordering. The enhanced antiferromagnetic behaviors are discussed with the effect of Fe-substitution, which reduce the magnetic frustration and enhance the exchange interaction.

Tuning the large magnetoelectric coupling in Co4Nb2O9 with Mn substitution

Magnetoelectric (ME) materials have been attracting extensive attention due to their potential applications. It is important to realize strong ME effect in one single material at sufficiently high temperature, and thus substantial efforts in searching for ME materials with strong ME coupling together and a comprehensive understanding of the underlying mechanism is necessary. Herein we focus on the Mn-doped linear ME material Co4-xMnxNb2O9, in which a large electric polarization driven by magnetic field emerges below its Néel temperature TN, by presenting the detailed characterizations on the structure, magnetism, and ME effect. It is revealed that an increasing Mn substitution x allows largely enhanced TN and gradually suppressed ME coefficient αME. This ME coupling suppression is attributed to the weak spin-orbit interaction of Mn2+ with respect to Co2+. It is indicated that the Dzyaloshinskii-Moriya (DM) interaction plays an important role in the ME coupling. The measured largest αME is found in For Co0.8Mn3.2Nb2O9, reaching up to 9.9 ps/m at 10 K while the TN reaches up to 102 K, exceeding most of the linear ME materials that have been reported.

Effect of transition metal element substitution on magnetoelectric properties of BiFeO3-BaTiO3 ceramics

BiFeO3 is the most typical multiferroic materials. However, the poor magnetoelectric coupling effect limits its practical application. In this work, the transition metal elements (Co, Mn) were introduced to suppress the spin cycloid structure of BiFeO3-based ceramics. The structure, ferroelectric, magnetic and magnetoelectric properties were investigated thoroughly. The XRD and SAED analysis confirmed the coexistence of tetragonal (T) and rhombohedral (R) phases of all samples. The piezoelectric properties were enhanced in Co-substituted samples. In addition, the magnetic properties were enhanced with the addition of Co/Mn ions. According to the analysis of the M-H loops and XRD patterns before and after poling, the electric-field induced magnetic change was observed in all samples, which can be attributed to the phase transition from R-phase to T-phase during poling. The room-temperature linear magnetoelectric coefficient αME was analyzed, and the maximum αME was obtained at BF-BT-005BC sample, where αME = 0.66 mV/cm Oe. The enhanced magnetic and magnetoelectric properties were ascribed to the distortion of the spiral spin structure by transition metal ions.

Magnetoelectric Properties of Zinc-Substituted BiFeO3 Multiferroics

The magnetoelectric properties of ceramic samples of BiFe1 – xZnxO3 and Bi1 – xZnxFe1 – xZnxO3 multiferroics have been studied in magnetic fields from 0 to 80 kOe at room temperature. All the samples have the linear dependences of magnetoelectric coefficient αME with low hump-like maxima of αME at 10 kHz and also at 85 kHz. These magnetoelectric studies of the bismuth ferrites with doubly substituted Zn show that the double substitution of Zn2+ ions for Bi3+ and Fe3+ ions does not lead to desired enhancement of the magnetoelectric properties as compared with the ordinary substitution of Zn2+.

Магнитоэлектрические свойства мультиферроиков BiFeO-=SUB=-3-=/SUB=- замещенных цинком

The magnetoelectric properties of ceramic samples of multiferroics BiFe1-xZnxO3 and Bi1-xZnxFe1-xZnxO3 were studied in the magnetic field from 0 to 80 kOe at room temperature. All samples have linear dependences of the magnetoelectric coefficient αME with small hump-like maxima αME both at c 10 kHz and at 85 kHz. Magnetoelectric studies in samples of bismuth ferrite series with double substituted Zn show that double substitution of Bi3+ and Fe3+ ions by Zn2+ ions does not give the desired enhancement of magnetoelectric properties.

Structural, dielectric, and multiferroic properties of Ta2O5-modified BiFeO3–BaTiO3–LaFeO3 solid solutions

In this work, a series of Ta2O5-doped 0.675BiFeO3–0.3BaTiO3–0.025LaFeO3−x mol% Ta2O5 (x = 0, 0.25, 0.50, 0.75, 1.0, 1.25) multiferroic ceramics were synthesized by solid-state reaction. The effects of Ta5+ doping on their phase structure, morphology, dielectric, ferroelectric, magnetic, and magnetoelectric properties were assessed. All samples were found to crystallize in perovskite structures, and the grain size was remarkably decreased by Ta5+ doping. Ta2O5 was beneficial to the dielectric properties, with the dielectric constant rising from 829 for undoped ceramic to 1149 for x = 1.25 at 100 Hz. The remnant polarization Pr and coercive field Ec decreased as x increased, indicating the worsening of ferroelectric behavior. In comparison, the ferromagnetism was evidently enhanced with increasing content of Ta2O5, and the remanent magnetization Mr peaked at 0.035 emu/g for x = 0.75. The magnetoelectric coefficient αME reached the maximum (418.68 mV/cm·Oe) for x = 0.25 at 200 Oe and 105 Hz.

Magnetoelectric and HR-STEM investigations on eutectic CoFe2O4–Ba1–xSrxTiO3 composites

Multiferroic Ba1–xSrxTiO3–CoFe2O4 (x = 0.03, 0.05) composites with rarely investigated 3-3 connectivity were prepared by eutectic crystallization in an optical floating zone furnace. High-resolution scanning transmission electron microscopy investigations of the CoFe2O4–BaTiO3 interface revealed an almost perfect connection between both components. These micrographs also showed that the impact of post-annealing in air was much larger than expected and resulted in formation of small BaTiO3 inclusions in the CoFe2O4 phase. The magnetoelectric coefficient αME was studied in detail with respect to its dependence on the static magnetic field, the frequency of the driving AC-field and temperature. Furthermore, the influence of different growth rates (5, 10 and 20 mm h−1), chemical composition, sample thickness and the alignment of electrical polarization and magnetic field (collinear or vertical) on the magnetoelectric properties were studied. The largest value of αME = 1.3 mV Oe−1 cm−1 was found for a sample grown at 5 mm h−1. For even slower growth rates, a higher Sr content was required to avoid the formation of impurity phases leading to a decrease of αME.

Frequency-tunable nickel-titanium substrates for magnetoelectric sensors

We show the use of nickel-titanium (NiTi) metal thin films as functional substrates of magnetoelectric composites allowing the composites’ mechanical resonance to be tuned towards the frequency range of interest by employing the gradual change of the Young’s modulus during the martensite-austenite phase transformation. Such composites are successfully fabricated by layering functional piezoelectric aluminum nitride and highly magnetostrictive FeCoSiB on sputtered NiTi-films. Subsequent characterizations reveal high magnetoelectric response. Applied as magnetic field sensors a high sensitivity (with a magnetoelectric coefficient αME=290 V/cm Oe) and low limit of detection of approximately 110 pT/Hz1/2 is observed for AC magnetic fields matching the mechanical resonance frequency. This mechanical resonance of the sensor can be altered with a Δf of 12% in the temperature interval between room temperature and 130 °C. This offers the possibility to adjust the sensor’s mechanical resonance frequency featuring the highest sensitivity to the magnetic field frequency to be measured.

Enhancing the magnetoelectric coupling of Co4Nb2O9[100] by substituting Mg for Co

We report experimental studies on enhancing the magnetoelectric (ME) coupling of Co4Nb2O9 by substituting the non-magnetic metal Mg for Co. A series of single crystal Co4–xMgxNb2O9 (x = 0, 1, 2, 3) with a single-phase corundum-type structure are synthesized using the optical floating zone method, and the good quality and crystallographic orientations of the synthesized samples are confirmed by the Laue spots and sharp XRD peaks. Although the Neel temperatures (TN) of the Mg substituted crystals decrease slightly from 27 K for pure Co4Nb2O9 to 19 K and 11 K for Co3MgNb2O9 and Co2Mg2Nb2O9, respectively, the ME coupling is doubly enhanced by Mg substitution when x = 1. The ME coefficient αME of Co3MgNb2O9 required for the magnetic field (electric field) control of electric polarization (magnetization) is measured to be 12.8 ps/m (13.7 ps/m). These results indicate that the Mg substituted Co4–xMgxNb2O9 (x = 1) could serve as a potential candidate material for applications in future logic spintronics and logic devices.

Correlation of High Magnetoelectric Coupling with Oxygen Vacancy Superstructure in Epitaxial Multiferroic BaTiO₃-BiFeO₃ Composite Thin Films.

Epitaxial multiferroic BaTiO3-BiFeO3 composite thin films exhibit a correlation between the magnetoelectric (ME) voltage coefficient αME and the oxygen partial pressure during growth. The ME coefficient αME reaches high values up to 43 V/(cm·Oe) at 300 K and at 0.25 mbar oxygen growth pressure. The temperature dependence of αME of the composite films is opposite that of recently-reported BaTiO3-BiFeO3 superlattices, indicating that strain-mediated ME coupling alone cannot explain its origin. Probably, charge-mediated ME coupling may play a role in the composite films. Furthermore, the chemically-homogeneous composite films show an oxygen vacancy superstructure, which arises from vacancy ordering on the {111} planes of the pseudocubic BaTiO3-type structure. This work contributes to the understanding of magnetoelectric coupling as a complex and sensitive interplay of chemical, structural and geometrical issues of the BaTiO3-BiFeO3 composite system and, thus, paves the way to practical exploitation of magnetoelectric composites.

Exchange biased magnetoelectric composites for magnetic field sensor application by frequency conversion

A comparison is presented between magnetoelectric composite sensors based on AlN and FeCoSiB with and without exchange bias coupling. All layer stacks were fabricated by thin film deposition on Si substrates. Whereas sensors without exchange bias exhibit a low limit of detection in the 1 pT/√Hz regime for resonant AC fields, such sensors fail at the detection of low frequency signals. Accordingly, their detection limit increases to about 10 nT/√Hz for alternating magnetic fields with 10 Hz frequency and an integration time equal to 3 s. A frequency conversion technique based on magnetic modulation of the sensors improves their detection limit by about one order of magnitude. However, frequency conversion can be applied more effectively to magnetoelectric sensors with exchange biased multilayers as a magnetostrictive phase. As a result, their limit of detection is about 180 pT/√Hz for 10 Hz signals and an integration time of 1 s. This is in contrast to the magnetoelectric coefficient αME of the two types of sensors. Whereas αME equals 6.9 kV/cm Oe for non-biased composites and resonant fields, it is by a factor of 8 smaller for the exchange biased composites. The nonetheless arising improvement of sensor performance with regard to the limit of detection for magnetic fields with low frequencies can be explained by a significantly lower magnetic noise contribution during modulation of the exchange biased sensors.

Multiferroic BaTiO3–BiFeO3 composite thin films and multilayers: strain engineering and magnetoelectric coupling

BiFeO3 and BaTiO3 were used to grow homogeneous composite thin films and multilayer heterostructures with 15 double layers by pulsed laser deposition. The perpendicular strain of the films was tuned by employing different substrate materials, i.e. SrTiO3(0 0 1), MgO(0 0 1) and MgAl2O4(0 0 1). Multiferroic properties have been measured in a temperature range from room temperature down to 2 K. The composite films show a high ferroelectric saturation polarization of more than 70 µC cm−2. The multilayers show the highest magnetization of 2.3 emu cm−3, due to interface magnetic moments and exchange coupling of the included weak ferromagnetic phases. The magnetoelectric coupling of the BaTiO3–BiFeO3 films was investigated by two methods. While the ferroelectric hysteresis loops in magnetic fields up to 8 T show only minor changes, a direct longitudinal AC method yields a magnetoelectric coefficient αME = ∂E/∂H of 20.75 V cm−1 Oe−1 with a low μ0HDC of 0.25 T for the 67% BaTiO3–33% BiFeO3 composite film at 300 K. This value is close to the highest reported in the literature.

The magnetostrictive and magnetoelectric characterization of Ni0.3Zn0.62Cu0.08Fe2O4–Pb(FeNb)0.5O3 laminated composite

Magnetoelectric effect in multiferroic materials is widely studied for its fundamental interest and practical applications. The magnetoelectric effect observed for single phase multiferroics is usually small. A much larger effect can be obtained in composites consisting of magnetostrictive and ferroelectric phases. This paper investigates the magnetoelectric effect of multilayer (laminated) structure consisting of 7 nickel ferrite and 8 PFN relaxor layers. It describes the synthesis and tape casting process for Ni0.3Zn0.62Cu0.08Fe2O4 ferrite and relaxor PbFe0.5Nb0.5O3 (PFN). Magnetic susceptibility, hysteresis, ZFC–FC curves and dependencies of magnetization versus temperature for PFN relaxor and magnetoelectric composite were measured with a vibrating sample magnetometer (VSM) in an applied magnetic field up to 85kOe at a temperature range of 10–400K. Parallel and perpendicular magnetostriction of the pure ferrite and bulk and laminated composites were measured at room temperature as a function of the magnetic field (0.3–6.5kOe). Magnetoelectric effect at room temperature was investigated as a function of the static magnetic field (0.3–6.5kOe) and the frequency of the sinusoidal magnetic field (0.01–6.5kHz). At lower magnetic field, the magnetoelectric coefficient increases slightly before reaching a maximum and then decreases. The magnetoelectric coefficient αME increases continuously as the frequency is raised, although this increase is less pronounced in the 1–6.5kHz range. The maximum values of magnetoelectric coefficient attained for the layered composites exceed about 50mV/(Oecm).

MEMS magnetic field sensor based on magnetoelectric composites

For the measurement of biomagnetic signals in the pico- and femtotesla regime superconducting interference devices (SQUIDs) are commonly used. Their major limitation comes from helium cooling which makes these sensors bulky and expensive. We show that MEMS sensors based on magnetoelectric (ME) composites could be capable as a replacement for biomagnetic measurements. Using surface micromachining processes a cantilever beam with a stack composed of SiO2/Ti/Pt/AlN/Cr/FeCoSiB was fabricated on a 150 mm Si (1 0 0) wafer. First measurements of a rectangular micro cantilever with a thickness of 4 µm and lateral dimensions of 0.2 mm × 1.12 mm showed a giant ME coefficient αME = 1000 (V m−1)/(A m−1) in resonance at 2.4 kHz. The resulting static ME coefficient is αME = 14 (V m−1)/(A m−1). In resonance operation a sensitivity of 780 V T−1 and noise levels as low as 100 pT Hz−1/2 have been reached.

Magnetoelectric coupling in multiferroic heterostructure of rf-sputtered Ni–Mn–Ga thin film on PMN–PT

In this paper, we report a preparation of multiferroic heterostructure from thin film of Ni–Mn–Ga (NMG) alloy and lead magnesium niobate–lead titanate (PMN–PT) with effective magnetoelectric (ME) coupling between the film as ferromagnetic material and PMN–PT as piezoelectric material. The heterostructure was prepared by relatively low temperature (400°C) deposition of the film on single crystal of piezoelectric PMN–PT substrate using rf magnetron co-sputtering of Ni50Mn50 and Ni50Ga50 targets. Magnetic measurements by Superconducting Quantum Interference Design (SQIUD) Magnetometer and Vibrating Sample Magnetometer (VSM) on the film revealed that the film is in ferromagnetically ordered martensitic state at room temperature with saturation magnetization of ∼240emu/cm3 and Curie temperature of ∼337K. Piezoresponse force microscopy (PFM) measurement done at room temperature on the substrate showed the presence of expected hysteresis loop confirming the stability of the piezoelectric state of the substrate after deposition. Room temperature ME voltage coefficient (αME) of the heterostructure was measured as a function of applied bias dc magnetic field in Longitudinal–Transverse (L–T) ME coupling mode by lock-in technique. A maximum ME coefficient αME of 3.02mV/cmOe was measured for multiferroic NMG/PMN–PT heterostructure which demonstrates that there is ME coupling between the film as ferromagnetic material and PMN–PT as piezoelectric material.

Theoretical analyses on effective magnetoelectric coupling coefficients in piezoelectric/piezomagnetic laminates

In previous theoretical analyses, magnetoelectric (ME) coupling coefficient αME of piezoelectric/piezomagnetic laminates for static and dynamic modes is usually regarded as one that is not related to laminates’ sizes (length and width). In micrometer or sub-millimeter ME laminates, the decrease in ME coupling was normally attributed to the substrate’s clamping effect. Here, we report an effective ME coefficient αME,eff including sizes’ effect based on magnetic circuit method including the size induced demagnetization effect, which predicted that as sizes of ME laminates decrease from 100 mm to 10−3 mm, αME,eff will dramatically decreases from ∼5 V/cm-Oe to 0.08 V/cm-Oe. Size decrease in ME laminates will result in a decrease in effective magnetic induction Bμ inside piezomagnetic phase in an applied magnetic field H. Our analyses further disclose a degenerate mode occurred between the longitudinal and transverse resonance modes, which may cause a weakened ME coupling. Finally, our analyses indicate that a thin and long ME laminate will exhibit a stronger ME coupling, which was then confirmed by our experimental results.