Strain-mediated Magnetoelectric Effect Research Articles

Remotely Controlled Surface Charge Modulation of Magnetoelectric Nanogenerators for Swift and Efficient Drug Delivery.

We have developed a highly efficient technique of magnetically controlled swift loading and release of doxorubicin (DOX) drug using a magnetoelectric nanogenerator (MENG). Core-shell nanostructured MENG with a magnetostrictive core and piezoelectric shell act as field-responsive nanocarriers and possess the capability of field-triggered drug release in a cancerous environment. MENGs generate a surface electric dipole when subjected to a magnetic field due to the strain-mediated magnetoelectric effect. The capability of directional magnetic field-assisted modulation of the surface electrical dipole of MENG provides a mechanism to create/break ionic bonds with DOX molecules, which facilitates efficient drug attachment and on-demand swift detachment of the drug at a targeted site. The magnetic field-assisted drug-loading mechanism was minutely analyzed using spectrophotometry and Raman spectroscopy. The detailed time-dependent analysis of controlled drug release by the MENG under unidirectional and rotating magnetic field excitation was conducted using field-emission scanning electron microscopy, energy-dispersive X-ray, and atomic force microscopic measurements. In vitro, experiments validate the cytocompatibility and magnetically assisted on-demand and swift DOX drug delivery by the MENG near MCF-7 breast cancer cells, which results in a significant enhancement of cancer cell killing efficiency. A state-of-the-art experiment was performed to visualize the nanoscale magnetoelectric effect of MENG using off-axis electron holography under Lorentz conditions.

Dynamic magnetoelectric effect in bismuth-layer structured Aurivillius ceramics

Multiferroic materials have been developed and studied for decades due to their potential applications in microelectronics and spintronics, such as multi-state digital memories, energy storage, and ultra-fast electric field-controlled magnetic sensors. Among these materials, magnetoelectric multiferroics exhibit a magnetoelectric (ME) interaction allowing for the manipulation of polarization by a magnetic field and magnetization by an electric field through internal strain and/or charge. However, strain-mediated ME effect is time-consuming and inefficient at high frequencies (∼ GHz). To address this issue and pave the way toward high frequency applications of ME multiferroics, we have systematically designed and characterized layered Bi5FeTi3O15-type Aurivillius ceramics for a strong dynamic ME coupling in the GHz band. By introducing cobalt and niobium ions into Bi4.3Gd0.7FeTi3O15, a phase evolution from a four-layered structure to a mixed structure consisting of four- and three-layered phases was revealed. The Co/Nb co-doping was found to enhance the magnetization at room temperature while preserving ferroelectricity. The understanding of the substitution-enhanced dynamic ME coupling at satellite and radar communication frequencies is expected to broaden the range of applications for ME multiferroics.

Polarization-induced magnetoelectric effect in Fe3Ga/HfO2/Fe3Ga heterojunction

Fe3Ga/HfO2/Fe3Ga heterojunction possesses reasonable lattice mismatch and good ferroelectric at the nanoscale. However, its magnetoelectric coupling is unexplored. Based on the first-principles calculations, we demonstrate that the magnetoelectric coupling in Fe3Ga/HfO2/Fe3Ga heterojunction is induced by polarization, which is different from the common strain-mediated magnetoelectric effect. The polarization-induced magnetoelectric effect of heterojunction is explained by the analyses of orbital-resolved density of states and spin densities, finding that the interfaces between Fe3Ga and HfO2 play an important role in magnetoelectric coupling, offering an alternative pathway for generating magnetoelectric coupling at room temperature.

Investigations of room temperature multiferroic and magneto-electric properties of (1-Φ) PZTFT-Φ CZFMO particulate composites

Multiferroic composites consisting of a single-phase multiferroic [0.6(PbZr0.53Ti0.47O3)-0.4(PbFe0.5Ta0.5)O3] as a matrix and a magnetostrictive phase (Co0.6Zn0.4Fe1.7Mn0.3O4) dispersed in the matrix are fabricated via hybrid synthesis technique. The structure and surface morphology studies using x-ray diffraction and field emission scanning electron microscopy techniques indicate the formation of 3-0 type particulate composites. Coexistence of soft-magnetic behavior and ferroelectric characteristics are confirmed for composites from magnetization vs magnetic field (M–H) and polarization vs electric field (P–E) measurements, respectively. Magneto-dielectric (MD) measurement shows significant changes in the dielectric properties with the application of a magnetic field, indicating the existence of strong MD behavior. The biquadratic nature of magneto-electric (ME) coupling is described by the Landau free energy equation arising from the strain transfer at the interfaces between the constituent phases. The direct magneto-electric voltage coefficient measurement also confirms very strong coupling between ferroelectricity and magnetism and supports the strain-mediated magneto-electric effect in composites. The Φ = 0.3 composite exhibits the maximum ME coefficient of 20.72 mV/cm Oe with MS = 24.62 emu/g, HC = 59.66 Oe, and piezoelectric coefficient value d33 = 19 pC/N. The strong magneto-electric effect along with low dielectric loss at room temperature in these composites suggests their suitability for multifunctional magneto-electric device applications such as magnetic sensors, etc.

Vector analysis of electric-field-induced antiparallel magnetic domain evolution in ferromagnetic/ferroelectric heterostructures

Electric field (E-field) control of magnetism based on magnetoelectric coupling is one of the promising approaches for manipulating the magnetization with low power consumption. The evolution of magnetic domains under in-situ E-fields is significant for the practical applications in integrated micro/nano devices. Here, we report the vector analysis of the E-field-driven antiparallel magnetic domain evolution in FeCoSiB/PMN-PT(011) multiferroic heterostructures via in-situ quantitative magneto-optical Kerr microscope. It is demonstrated that the magnetic domains can be switched to both the 0° and 180° easy directions at the same time by E-fields, resulting in antiparallel magnetization distribution in ferromagnetic/ferroelectric heterostructures. This antiparallel magnetic domain evolution is attributed to energy minimization with the uniaxial strains by E-fields which can induce the rotation of domains no more than 90°. Moreover, domains can be driven along only one or both easy axis directions by reasonably selecting the initial magnetic domain distribution. The vector analysis of magnetic domain evolution can provide visual insights into the strain-mediated magnetoelectric effect, and promote the fundamental understanding of electrical regulation of magnetism.

Manipulation of Magnetization Reversal by Electric Field in a FePt/(011)PMN-PT/Au

Electric field manipulation of magnetism and 180° magnetization reversal are crucial for realizing magnetic storage devices with low-power consumption. Here, we demonstrate that electric-field manipulation of magnetic anisotropy rotation is achieved by the strain-mediated magnetoelectric effect in a Fe50Pt50/(011)0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3/Au. The remanent magnetization and magnetic coercivity of the Fe50Pt50 film exhibit an obvious response with the change of the electric fields. Moreover, the reversible in-plane 180° magnetization reversal can be controlled by alternating on or off the electric field under a small bias magnetic field. These results suggest a promising application for realizing magnetoelectric random access memory (MeRAM) devices with low-power consumption.

Shear-strain-induced over 90° rotation of local magnetization in FeCoSiB/PMN-PT (011) multiferroic heterostructures

Strain-mediated magnetoelectric effect can be utilized as an energy-efficient approach for spin manipulation. However, over 90° magnetization rotation is still challenging in un-patterned magnetic films, as the piezo-strain driven by ferroelectric domain switching is generally uniaxial rather than unidirectional, which limits the developments of non-volatile magnetic memory and logic devices. Here we demonstrate the rotation of local magnetization with a large angle of 136° by applying strains with a shear component at a fixed magnetic field of 45 Oe in FeCoSiB/PMN-PT (011) multiferroic heterostructures, revealed by a vector-resolved quantitative magneto-optical Kerr effect (MOKE) microscopy. Phase-field simulations confirm that the approximate 140° rotation of magnetization vectors is a consequence of the shear strain associated with ferroelectric/ferroelastic switching of PMN-PT (011) substrates. The visualization of over 90° magnetization rotation induced by the strain with a shear component paves the way for deterministic magnetization switching that has important implications in the energy-efficient spintronic devices.

Magnetic field control of polarization/capacitance/voltage/resistance through lattice strain in BaTiO3-CoFe2O4 multiferroic nanocomposite

Magnetoelectric (ME) nanocomposites is a topic of intensive research due to their superficial potential in spintronic applications. In the present work, the magnetic field controlled electrical polarization is studied in hydrothermally synthesized multiferroic 0.25BaTiO3-0.75CoFe2O4 (BTO-CFO) nanocomposite. This multiferroic heterostructure is combined ferrimagnetic (CFO) with ferroelectric/piezoelectric (BTO) and achieved strain-mediated ME effect, which can effectively mediate magnetic anisotropy. The X-ray diffraction pattern confirmed polycrystalline phases of spinel CFO and tetragonal BTO, for which the compressive lattice strain is made. The microstructural study has evaluated BTO-CFO nanoparticles formation and the value of d-lattice spacing is calculated. The room temperature magnetic hysteresis is arising which depends on CFO inversion degree, and the change in bond-angle/length along A and B-sites. The ferroelectric hysteresis is measured at room temperature, which changed with applied magnetic field, i.e., the phenomenon of reduction in domain wall pinning related with oxygen vacancies and grain boundaries effect. The magnetic field is also influenced impedance spectra to induce magnetoimpedance effect and the positive value of magnetoresistance is obtained. A giant magnetodielectric coefficient up to −27% is obtained at 1 kOe of field. A strain mediated ME coupling enhancement is obtained.

Electrical tuning of microwave properties via strain-mediated magnetoelectric coupling in multiferroic composites

Electrical field induced electromagnetic properties via strain-mediated magnetoelectric effect were studied in FeCoNi/[Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32 (PMN-PT) multiferroic heterostructures. Both the resonance frequency fFMR and the frequency linewidth Δf are electrically tunable with fFMR being varied from 3.8 to 8.1 GHz and Δf from 0.66 to 3.6 GHz. The static magnetic characterization result of the sample before and after poling is also in good agreement with the dynamic magnetic measurement. These results were discussed in details within the framework of the strain-mediated magnetoelectric coupling, which was firmly supported by the electrical field dependence of the in-plane strain measured by a strain gauge.

Strain-mediated magnetoelectric effect for the electric-field control of magnetic states in nanomagnets

Electric-field control of magnetism without electric currents potentially revolutionizes spintronics toward ultralow power. Here, by using mechanically coupled phase field simulations, we computationally demonstrate the application of the strain-mediated magnetoelectric effect for the electric-field control of magnetic states in a heterostructure. In the model heterostructure constituted of the soft nanomagnet Co and the piezoelectric substrate PMN–PT, both the volatility of magnetic states and the magnetization switching dynamics excited by the electric field are explored. It is found that an electric field can drive the single-domain nanomagnet into an equilibrium vortex state. The nanomagnet remains in the vortex state even after removing the electric field or applying a reverse electric field, i.e., the vortex state is extremely stable and nonvolatile. Only by utilizing the precessional magnetization dynamics, the 180 $$^\circ $$ magnetization switching is possible in small-sized nanomagnets which are free of the stable vortex state. Electric-field pulses can realize the deterministic 180 $$^\circ $$ switching if the electric-field magnitude, pulse width, and ramp time are carefully designed. The minimum switching time is found to be less than 10 ns. These results provide useful information for the design of low-power, reliable, and fast electric-field-controlled spintronics.

Discovery of Enhanced Magnetoelectric Coupling through Electric Field Control of Two-Magnon Scattering within Distorted Nanostructures.

Electric field control of dynamic spin interactions is promising to break through the limitation of the magnetostatic interaction based magnetoelectric (ME) effect. In this work, electric field control of the two-magnon scattering (TMS) effect excited by in-plane lattice rotation has been demonstrated in a La0.7Sr0.3MnO3 (LSMO)/Pb(Mn2/3Nb1/3)-PbTiO3 (PMN-PT) (011) multiferroic heterostructure. Compared with the conventional strain-mediated ME effect, a giant enhancement of ME effect up to 950% at the TMS critical angle is precisely determined by angular resolution of the ferromagnetic resonance (FMR) measurement. Particularly, a large electric field modulation of magnetic anisotropy (464 Oe) and FMR line width (401 Oe) is achieved at 173 K. The electric-field-controllable TMS effect and its correlated ME effect have been explained by electric field modulation of the planar spin interactions triggered by spin-lattice coupling. The enhancement of the ME effect at various temperatures and spin dynamics control are promising paradigms for next-generation voltage-tunable spintronic devices.

Electric-field control of magnetism in the flexible CoFeB/P(VDF–TrFE) multiferroic heterostructures

Flexible multiferroic heterostructures of ferromagnetic Co40Fe40B20/ferroelectric copolymer poly-vinylidene fluoride-trifluoroethylene [CoFeB/P(VDF-TrFE)] were fabricated by DC sputtering. The structure, ferroelectric behaviours along with remnant polarization (2Pr) of 2.4μC/cm2 at room temperature, saturated magnetizations around 900emu/cm3 were measured in the novel composites. Moreover, the direct electric field control of magnetic properties and the mechanisms of magnetoelectric (ME) coupling in the flexible CoFeB/P(VDF-TrFE) heterostructures were investigated, and the strong strain-mediated ME effect originating from voltage-induced piezo-strain was demonstrated. These results show the good prospects in application of flexible spintronic devices.

Lateral electric-field-driven non-volatile four-state memory in multiferroic heterostructures

A non-volatile four-state memory is formed using an in-plane side-polarization configuration in a Co/(011) Pb(Mg1/3Nb2/3)O3-PbTiO3 (Co/PMN-PT) heterostructure. The resistivity vs. electric field behavior shows a change from volatile butterfly to looplike to non-volatile butterfly characteristics when the temperature decreases from 290 K to 83 K under an electric field of 10 kV/cm and then increases back to 290 K; this behavior is attributed to the strain-mediated magnetoelectric effect. In addition, the in-plane resistivity of Co film, which was measured using the four-probe technique, can be controlled both electrically and magnetically. Specifically, a non-volatile resistivity is gained by the application of electric field pulses. Additionally, a four-state memory is obtained by co-mediation of the magnetic field and electric field pulses, compared with the two different states achieved under the application of the electric field only, which indicates that our results are highly important for multi-state memory and spintronic devices applications.

The effects of interface misfit strain and surface tension on magnetoelectric effects in layered magnetostrictive-piezoelectric composites

A nonlinear model is proposed to study low-frequency magnetoelectric (ME) effects in layered magnetostrictive-piezoelectric composites, taking into account the effects of interface misfit strain and surface stress. As a specific case, L-T mode of Terfenol-D/lead zirconate titanate (PZT) composites is investigated. The results show that flexural deformation can suppress the ME voltage coefficient, especially for elevated Terfenol-D volume fraction. Interface misfit strain demonstrates a notable impact on the ME voltage coefficient, and this strain-mediated ME effect is intensified with increasing interface misfit strain. Owing to residual surface tension, the ME voltage coefficient is found to be size-dependent when the thickness of Terfenol-D/PZT layered composite reduces to the nanoscale. In addition, substrate effect on ME voltage coefficients is evaluated.

Magnetodielectric effect in lead-free multiferroic CoFe2O4/K0.5Na0.5NbO3 bilayers

In this letter we presented the investigations of magnetodielectric (MD) effect in lead-free multiferroic CoFe2O4/Na0.5K0.5NbO3 (CFO/KNN) bilayers with constant volumes. The CFO/KNN bilayers were synthesized on conductive Nb-doped SrTiO3 (001) single-crystal substrates by radio frequency magnetron sputtering. Noticeable MD effect was observed in these CFO/KNN bilayers. The MD coefficient depends on the volume fraction of CFO layer. A maximum MD coefficient of about 7% at 12kOe at 2kHz was observed in 0.6CFO/0.4 KNN bilayer. The MD effect is attributed to strain-mediated magnetoelectric effect and magnetoresistance effect combined with the Maxwell–Wagner effect. The MD effect may have possible applications in magnetic field sensing devices.

Multiferroic magnetic recording read head technology for 1Tbit∕in.2 and beyond

Multiferroic (MF) materials are very promising candidates for new technologies and applications because they exhibit simultaneously multiple cooperative phenomena (i.e., magnetic, electric, and piezoeffects). The main feature of MF materials is the magnetoelectric (ME) effect, which can be used to engineer highly sensitive magnetic/electric sensors. In this paper, we discuss the requirements of a new kind of magnetic recording read head for 1Tbit∕in.2 recording densities, which is based on a MF structure. The MF sensor operates at room temperature via the strain mediated ME effect by producing a voltage signal in response to the magnetic field excitation from the recorded bits. We calculated the theoretical output from such a recording read head assuming a magnetic recording density of 1Tbit∕in.2. Our calculations demonstrate that the proposed read head technology could replace in the future the conventional magnetoresistive read heads bringing also a number of considerable advantages, as detailed in the paper.