Papers by Keyword: Magnetoelectric

Abstract: The magnetic structure of the one-dimensional (1D) compounds A₃MXO₆ (where A is Ca or Sr, M and X are transition metal cations) can be tuned from collinear to spiral by merely changing the identity of the M and X atoms constituting the 1D chains. This suggests the prospect of realizing ferroelectricity that is induced by different types of magnetic order. To date, magnetism-driven ferroelectricity in these 1D compounds has only been discovered in Ca₃CoMnO₆ with a collinear magnetic structure, whereas other magnetic structures such as spin spirals have been much less discussed. Here, the magnetoelectric effect in 1D Ca₃NiMnO₆ with a spiral magnetic structure is investigated. The presence of magnetoelectric coupling in the sample is evidenced by changes in capacitance of up to 1.5 % in an applied magnetic field of 8 T at a temperature of 5 K. These results highlight the relation between magnetic and electric order in 1D compounds with a spiral magnetic structure and provide more insight into magnetoelectric coupling mechanisms in 1D compounds in general.

Abstract: Magnetoelectric materials which simultaneously exhibit ferroelectricity and magnetism have attracted great attention in recent years due to their potent coupling effect, and potential application in the electronics industry. The work done in this study aims to investigate the effect of ferromagnetic (Fe₃O₄) nanoparticles on the thermal, mechanical, magnetic, and ferro-electrical properties of PVDF, and its co-polymer poly (vinlydene fluoride-co-trifluoroethylene), P (VDF-TrFE). These compounds are synthesized into flexible nanocomposite thin films, via a novel solvent casting method to influence crystallization and nucleation growth. Fe₃O₄ nanoparticles (NP) were integrated with polymers at varying weight percentages (1wt%, 3wt%, 5wt%, 7wt%, and 10wt %). Magnetoelectric nanocomposites were annealed at 150oC. Films were fabricated and processed at dimensions: 8-20μm thickness, 35 mm length, and 35 mm width. Neat and loaded samples are characterized using x-ray diffraction (XRD) to observe crystallinity and to obtain β - phase content distribution. Ferroelectric hysteresis loops are given from Radiant Multiferroic Analyzer, which resulted in an increase in peak polarization of 9.601μC/cm² with the addition of 5wt% magnetite nanoparticles to P(VDF-TrFE) polymer blend. Magnetic tests are done using Vibrating Sample Magnetometer (VSM), which yields the magnetic polarization with respect to changes in field magnitude. The highest magnetic moment occurs with the addition of 10wt% Fe₃O₄ nanoparticles at 3.66 emu/g. Target applications of nanocomposites are for microelectromechanical system (MEMS) devices such as memory cards, spintronic, sensors, electromagnetic shielding, and compact energy storage.

Abstract: Magneto-electric composites of two distinct phases, ferrimagnetic-piezoelectric system with general compositional formula (x) ferromagnetic + (1-x) piezoelectric were synthesized using a hybrid technique, mechano-chemical method by sintering the mixtures of piezo-electric BaTiO3 (BTO) and ferri-magnetic Mg0.2Cu0.5Zn0.3Fe2O4 (MCZF). Here, ferri-magnetic phase component MCZF (Mg0.2Cu0.5Zn0.3Fe2O4) was prepared using auto-combustion method, whereas piezo-electric BTO was procured commercially from Sigma-Aldrich. Here, the general composition of composites is given by (x) Mg0.2Cu0.5Zn0.3Fe2O4+(1-x) BaTiO3(x=15%, 30% and 45%). Presences of two phases in these magneto-electric composites were probed using X-ray diffraction (XRD) studies. Peaks observed in the XRD spectrum indicated spinel cubic structure for MCZF ferrite and tetragonal perovskite structure for BTO and, both spinel and pervoskite structures for synthesized composites. Micro-structure of the samples has been investigated using Field Emission Scanning Electron Microscope (FESEM). Frequency dependent dielectric properties of synthesized composites were measured from 100 Hz to 1 MHz at room temperature using a precision HIOKI make LCR HI-TESTER. Dielectric dispersion was observed at lower frequencies for the synthesized composites.

Abstract: Soft magnetic material FeCoV is sensitive to magnetic field and its cost is lower than giant magnetostriction materials (Terfenol-D et al.). In the present investigation Pb (Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) with different thickness and FeCoV laminate with 0.8mm thickness were assembled into layer structure to study the effect of the PMN-PT volume fraction on the magnetoelectric coefficient of PMN-PT/FeCoV laminate composites. The ME coefficients and voltages have been characterized in the longitudinally magnetized and transversely polarized mode. The measurement was conducted under a static magnetic field superimposed with an alternating magnetic field. The influences of the static and the alternating field strength were discussed. The peak ME coefficient was obtained at 430 Oe. With the volume fraction of PMN-PT increased, the ME coefficient decreased within the experiment fraction. It can be explained by the module of M.I.Bichurin. A linear relationship was observed between the magnetoelectric voltage and the alternating field strength under a static field of 400 Oe. The ME voltage decreased when the PMN-PT volume fraction increased in the experiment fraction.

Abstract: The intermediated strain can convert a magnetic field to an electric output signal in a magnetostrictive-piezoelectric layered composite via three parameters: the magnetoelastic coupling, the piezoelastic coupling and the mechanical impedance. These three parameters are dominated respectively by the magnetostrictive coefficient, the piezoelectric coefficient and the mean flexibility of material in the composite. Focusing on these three parameters, many investigations on the ME enhancement have been carried out by choosing the correct material or by adjusting the ratio between the two phases in the composite [4]. Thereafter, the noise performance of ME laminates has been studied for applications as a magnetic sensor. In the last several years, the intrinsic noise sources for both the composite and the amplifier circuit have been mathematically modeled and experimentally characterized. The passively sensed signal can be amplified by either a voltage or a charge method. Furthermore, the noise contributions from the detection electronics were also integrated in the noise performance analysis [5]. According to these studies, dielectric dissipation in the piezoelectric phase is the main contribution to the noise floor for low-frequency magnetic field sensing even though the equivalent current noise source from the electronics induce fluctuations in the output signal of the low-frequency charge detection as well [6].

Abstract: La_0.67Sr_0.33MnO₃ (LSMO)/Pb_0.92La_0.08Zr_0.65Ti_0.35O₃ (PLZT) composite film was fabricated on a (001) LaAlO₃ (LAO) single crystal substrate by a sol-gel technique. The results from X-ray diffraction (XRD) indicated that LSMO and PLZT could grow successively on LAO substrate with (001) preferred orientation. The ferroelectric and ferromagnetic properties of LAO/LSMO/PLZT composite film were also investigated. The results showed that the remnant polarization P_r, and coercive field E_c of the composite film at room temperature were 36.38 μC/cm² and 512.43 kV/cm respectively. Moreover, the composite film exhibited significant ferromagnetic hysteresis loops and soft magnetic behavior at temperatures lower than 250 K.

Abstract: Sr_1-xGd_xCo₂Fe₁₆O_27-δ, (x = 0.05–0.20) was prepared via the proteic sol-gel process. Single-phase W-type hexaferrite doped with gadolinium was synthesized. The ferrite shows ferrimagnetic behavior with high saturation magnetization, low coercive field, low remnant magnetization, and a resistivity greater than 10⁷ Ω·cm. The substitution of Sr²⁺ for Gd³⁺ improved the magnetoelectric properties of the ferrite owing to the increase in the concentration of Fe²⁺ and improvement of electron conduction.

Abstract: This work involves the fabrication of high purity Pb (Zr,Ti)O₃ ferroelectric based in ceramic forms, and a study of the correlation between their compositions and electrical properties. In order to enhance multiferroic characteristics of Pb (Zr,Ti)O₃ ferroelectric based ceramics compound ferrites additives were added and the dielectric property as a function of magnetic field strength. Those are expected to explain multiferroic characteristics (ferroelectric-ferromagnetic coupling interaction) by quantitative evaluation which is the key to understand physical mechanism in coupling interaction to enhance multiferroic characteristics in materials.

Abstract: This paper reports on the multiphysics modelling of a bi-axial vibration energy harvesting (VEH) approach, with experimental validation of the model predictions. The authors have developed a harvester able to generate voltage under bi-axial vibrations. The harvesting approach is based on a magnetoelectric (ME) transducer that is positioned between a fixed magnet and oscillating ball bearing, which steers a changing magnetic field through the transducer to generate a voltage. The transducer combines magnetostrictive and piezoelectric properties to convert magnetic potential into electrical energy. Analytical modelling of this phenomenon is difficult due to the highly coupled nature of this interaction, so Comsol multiphysics software is used to make predictions of output using the finite element method (FEM). A peak open-circuit harvester voltage of 39.4 V is predicted for a ball bearing oscillating with 4.5 mm amplitude, agreeing reasonably well with measured harvester voltage of approximately 35 V. The modelling is applied to a two-dimensional representation of the system, which is shown to be sufficient for a basic understanding of the highly coupled nature of interactions, and a basis for optimising the magnetoelectric vibration energy harvesting approach.

Abstract: Spinel-perovskite multiferroics of NiFe₂O₄/BiFeO₃ nanoparticles were prepared by modified Pechini method. The structure and morphology of the composites were examined by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the composites consisted of spinel NiFe₂O₄ and perovskite BiFeO₃ after annealed at 700°C for 2h, and the particle size ranges from 40 to 100nm. VSM and ME results indicated that the nanocomposites exhibited both tuning magnetic properties and a ME effect. The ME effect of the nanocomposites strongly depended on the magnetic bias and magnetic field frequency.