Narrow Results

This paper discusses recent efforts to control magnetism with electric fields in single and multilayer oxides, which has great potential to improve a variety of technological endeavors, such as magnetic sensing and magnetoelectric (ME) logic. The importance of electrical control of magnetism is followed by a discussion of multiferroics and MEs, which are the leading contenders for this task. The focus of this paper is on complementary methods in understanding the ME coupling, an essential step to electrical control of magnetism. Neutron scattering, nonlinear optics and X-ray spectromicroscopy are addressed in providing key parameters in the study of ME coupling. While primarily direct (single-phase multiferroics) ME materials are used as examples, the techniques discussed are also valuable to the study of indirect (e.g., multilayers and pillars) magnetoelectrics. We conclude with a summary of the field and future directions.

FeCo/PZT/FeCo cylindrical heterostructures were prepared by electroless deposition. Scanning electron microscopy shows that the magnetostrictive FeCo layers are in contact with piezoelectric PZT directly. To control the resonant frequency at which the magnetoelectric coupling shows an obvious improvement, the height of cylinder needs to be taken into consideration. In the present work, three hollow cylinders with different height were polarized along the radial direction. It was shown that with the increase of cylinder height the magnetoelectric coefficient increased. Both experimental and calculated results show that the resonant frequency of FeCo/PZT/FeCo cylindrical layered composites decreases with increasing the cylinder height. Proper resonant frequency and strong ME effect could be obtained by optimizing the configuration.

The magnetoelectric (ME) properties of sol–gel grown BiFe${}_{0.95}$Co${}_{0.05}$O₃ (BFCO) nanoceramics, with different sizes, were investigated at room-temperature. X-ray diffraction (XRD) measurement was performed to investigate structural properties of the samples understudy. Magnetic field-dependent dielectric permittivity has been systematically investigated in the frequency range of 20 Hz to 1 MHz. To ensure the origin of magnetodielectric response, the magnetoimpedance (MI) spectroscopy was adopted using equivalent circuit model. The a.c. conductivity was found to obey the Jonscher’s universal power law. The modifications in spiral spin structure in the BFCO nanoparticles with size less than $\sim$62 nm significantly affect the ME coupling parameters.

The magnetoelectric (ME) effect in a ME composite structure in which a magnetostrictive component is bonded with a piezoelectric component was studied theoretically, based on the hyperbolic nonlinear constitutive relation of magnetostriction and the piezoelectric equations. A quantitative relation was established analytically for the ME effect and the influencing factors, such as the magnetic bias field and the structure dimensions. It was verified that the theoretical model agrees qualitatively with the experimental results published in Ref. 7. It can also be predicted by the model that the ME effect can be improved by optimizing the structure dimensions.

Magnetoelectric (ME) nickel and lead zirconium titanate multi-layers with neither electrodes nor bonding layers was developed by electroless deposition. Scanning electron microscopy reveals that the Ni layer is in direct contact with the PZT layer without inter-layer not only in Ni/PZT/Ni trilayer but also in Ni/PZT/Ni/PZT/Ni multi-layer. The in-plane parallel magnetostriction has been measured for electroless deposited Ni. The saturation magnetostriction is 32.6 × 10^-6. When the total thickness of multi-layers is the same, the ME voltage coefficient α_E,31 decreases with increasing the stacking periodicity. On condition that the thickness of each layer is the same, the ME voltage coefficient V_E,31 of the Ni/PZT/Ni/PZT/Ni multi-layer is nearly twice higher than that of the Ni/PZT/Ni tri-layer at the resonance frequency, which provides a new choice to obtain higher ME voltage coefficient.

Magnetoelectric (ME) Ni/Pb(Zr_0.52Ti_0.48)O₃ bilayers have been successfully prepared by hydrothermal method using Ti as buffer layer. The hydrothermal mechanism of PZT thin film deposited onto Ni layer has been discussed. The structure and ferroelectric properties of the deposited PZT thin films are characterized by X-ray diffraction and ferroelectric testing. The ME voltage coefficient of the Ni/PZT bilayers gradually decreases as the thickness of buffer layer increases because the interface coupling of the Ni/PZT layers gradually decreases. The large ME coefficient makes these Ni/PZT bilayers possible for applications in multifunctional devices such as electromagnetic sensor, transducers and microwave devices.

Magnetoelectric (ME) coupling in layered structures of magnetostrictive and piezoelectric phases are mediated by mechanical deformation and depends strongly on the interface conditions. Ni-lead zirconium titanate-Ni trilayers with neither electrodes nor bonding layers have been derived by electroless deposition. The structure of the electroless deposited Ni layer was characterized by X-ray diffraction. The cross-section of the Ni/PZT layers was investigated using scanning electron microscopy. The value of ME voltage coefficient (α_E,31) increases as the interface roughness increases. The maximum of α_E,31 for the Ni/PZT/Ni trilayers polarized after electroless deposition is higher than that for the Ni/PZT/Ni trilayers polarized before electroless deposition. It is essential to optimize the interface and the polarization to obtain higher ME voltage coefficient.

The Ni layers with good soft magnetic properties have been successfully electroless deposited on PZT layers. To study the thermodynamics and kinetics of electroless Ni-deposition, the effect of bath parameters such as pH and temperature has been discussed. The structural, magnetic and magnetostrictive properties of Ni layers deposited at various pH and temperature are characterized by X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer and standard strain-gauge technique. The grain size, deposition rate, magnetic properties and magnetostrictive properties of Ni layers and magnetoelectric effect of Ni/PZT/Ni trilayers depend strongly on the thermodynamics and kinetics of electroless deposition processes. A maximum ME voltage coefficient of α_E,31 = 5.8 V cm^-1 Oe^-1 is obtained at a frequency of about 101 kHz. These trilayers exhibit a promising potential in actuators, transducers and sensors.

Magnetoelectric (ME) effect has been studied in semicircular composites with a negative magnetostrictive/piezoelectric/positive magnetostrictive Ni/Pb(Zr,Ti)O₃/FeCo trilayered structure. The ME behavior of the Ni/Pb(Zr,Ti)O₃/FeCo is different from those in previous studies and zero-bias ME effects and four remarkable resonant peaks have been observed in the dependence of the ME voltage coefficient on the magnetic field frequency in the 1–150 kHz range. The effective excitation of the acoustical oscillations provided by the positive and negative magnetostrictive layers is responsible for the multifrequency ME effects. The results open up a suitable way to make multifunctional devices with multi-resonant-frequencies and/or zero-bias operations.

This review provides a comprehensive understanding of magnetoelectric (ME) nanocomposite, cobalt ferrite–barium titanate (CFO–BTO) as a potential candidate for targeting specific cells. The synthesized core–shell material uses strain-mediated coupling between magnetostrictive and piezoelectric material. CFO–BTO has the competitive advantage of a high ME coefficient and is biocompatible. The shape and size play a pivotal role in passive drug delivery due to the enhanced permeability and retention effect at tumor sites. Surfactants can also enhance drug absorption and influence the interaction with nanoparticle composite. A comparison between external magnetic field–frequency parameters to navigate the ME nanoparticle and trigger release of the drug at site is also reviewed. Coating the nanoparticles with a layer of surfactant can reduce the threshold external magnetic field for navigation and triggering of drug particle release, making the prospect viable for clinical studies.

Multiferroic materials have a unique ability to combine two or more ferroic orders within the same phase. Specifically, magnetoelectric (ME) materials exhibit a unique combination of three ferroic orders in their response to magnetic, elastic, and electric fields. This study focuses on a finite element investigation of a hybrid multilayer ME coupling, incorporating two different magnetostrictive materials in a single composite. The composite includes Nickel, exhibiting negative magnetostriction, leading to an increase in pre-compressive stress, easy machinability, and cost-effectiveness. Additionally, Terfenol-D is utilized due to its characteristic property of high magnetostrictive strain when exposed to an external magnetic field. The result of this study shows that this hybrid ME structure has an ME coefficient of 804 mV/cm. Oe without pre-stress and ME coefficient is increased to 32.64 V/cm. Oe by applying pre-stress while retaining cost-effectiveness. The analysis in this particular work also suggests promising applications for energy harvesting and magnetic field sensing.

Piezoelectric actuators operating in piezoelectric-induced strain/stress or electromechanical resonance-induced vibration or wave-motion friction drive mechanism have shown many advantages over traditional electromagnetic motors, especially, when miniaturizing into millimeter-scale size, while magnetoelectric actuators operating in magnetostrictive mechanism are capable of piezoelectric self-sensing and remote operation under an applied magnetic field. This paper summarizes the recent progresses in piezoelectric ceramic and single crystal materials based actuators and micromotors, ferromagnetic/ferroelectric laminated magnetoelectric actuators, including rotary, linear, planner, and spherical motion actuators, and bending motion magnetoelectric actuators. Their driving mechanisms, operation properties, and applications are also explained.

Multiferroic materials and devices have attracted intensified recent interests due to the demonstrated strong magnetoelectric (ME) coupling in new multiferroic materials and devices with unique functionalities and superior performance characteristics. Strong ME coupling has been demonstrated in a variety of multiferroic heterostructures, including bulk magnetic on ferro/piezoelectric multiferroic heterostructures, magnetic film on ferro/piezoelectric slab multiferroic heterostructures, thin film multiferroic heterostructures, etc. Different multiferroic devices have been demonstrated, which include magnetic sensors, energy harvesters, and voltage tunable multiferroic RF/microwave devices which are compact, lightweight, and power efficient. In this progress report, we cover the most recent progress on multiferroic heterostructures and devices with a focus on voltage tunable multiferroic heterostructures and devices with strong converse ME coupling. Recent progress on magnetic-field tunable RF/microwave devices are also covered, including novel non-reciprocal tunable bandpass filters with ultra wideband isolation, compact, low loss and high power handling phase shifters, etc. These novel tunable multiferroic heterostructures and devices and tunable magnetic devices provide great opportunities for next generation reconfigurable RF/microwave communication systems and radars, Spintronics, magnetic field sensing, etc.