Large Magnetoelectric Research Articles

Numerical modeling of magnetoelectric effect in a composite structure

The mechanical coupling effect in a magnetoelectric (ME) composite structure in which a magnetostrictive component is bonded with a piezoelectric one is simulated by numerical technique, focusing on an optimization of the magnetoelectric coupling output. The simulation starts from an experimentally developed ME composite structure and takes into account the mechanical coupling mechanism between the two components. A numerical optimization algorithm is developed, predicting a significant enhancement of the ME output by optimizing the component dimension. This algorithm can also be used for optimum design of other ME composite structures in terms of the largest ME output.

Magnetoelectric Effect in Composites of Magnetostrictive and Piezoelectric Materials

In the past few decades, extensive research has been conducted on the magnetoelectric (ME) effect in single phase and composite materials. Dielectric polarization of a material under a magnetic field or an induced magnetization under an electric field requires the simultaneous presence of long-range ordering of magnetic moments and electric dipoles. Single phase materials suffer from the drawback that the ME effect is considerably weak even at low temperatures, limiting their applicability in practical devices. Better alternatives are ME composites that have large magnitudes of the ME voltage coefficient. The composites exploit the product property of the materials. The ME effect can be realized using composites consisting of individual piezomagnetic and piezoelectric phases or individual magnetostrictive and piezoelectric phases. In the past few years, our group has done extensive research on ME materials for magnetic field sensing applications and current measurement probes for high-power electric transmission systems. In this review article, we mainly emphasize our investigations of ME particulate composites and laminate composites and summarize the important results. The data reported in the literature are also compared for clarity. Based on these results, we establish the fact that magnetoelectric laminate composites (MLCs) made from the giant magnetostrictive material, Terfenol-D, and relaxor-based piezocrystals are far superior to the other contenders. The large ME voltage coefficient in MLCs was obtained because of the high piezoelectric voltage coefficient of the piezocrystals and large elastic compliances. In addition, an optimized thickness ratio between the piezoelectric and magnetostrictive phases and the direction of the magnetostriction also influence the magnitude of the ME coefficient.

Anomalous photovoltaic effect in ZnS thin films: G Marchal and W Palz, Phys Stat Sol (a), 2 (4), Aug 1970, K257– K259

Ni0.5Zn0.5Fe2O4 (NZFO) + BiFeO3 (BFO) composite films were co-sputtered on (001) SrTiO3 (STO) substrates, which were confirmed to be epitaxial by both 1D and 2D X-ray diffractions. Conductive LaNiO3 (LNO) was sputtered on STO as bottom electrode for magnetoelectric (ME) measurement across film. The LNO layer was epitaxial and composed of nanocolumns perpendicular to substrate, which are helpful in reducing “substrate clamp” effect because of the flexibility of nanocolumns. NZFO + BFO films co-sputtered on LNO/STO were also epitaxial but both out-of-plane and in-plane textures of BFO were degraded with full width at half maximum of 1.974° and 2.55°, respectively, compared to 1.163° and 1.71° in films grown on bare STO. There were apparent tetragonal distortions in NZFO and BFO due to compressive in-plane strains imposed by epitaxial growth of larger NZFO and BFO lattices on smaller LNO lattice. Transmission electron microscopy (TEM) showed that the composite films were compact with clear boundaries between the NZFO and BFO phases, which were uniformly distributed with the ratio of about 35% NZFO and 65% BFO. Cross-sectional TEM revealed that crystallographic planes were very well aligned between BFO and LNO, but NZFO planes tilted 7.5° due to large lattice misfit. When measured vertically from LNO to top surface of composite film, large ME voltage coefficient at zero bias field was observed, which was 911 mVcm−1Oe−1 at the frequency of 8 kHz. This was ascribed to the large heteroepitaxial strains in composite films.