Converse Magnetoelectric Coupling Research Articles

Giant self-biased converse magnetoelectric effect in multiferroic heterostructure with single-phase magnetostrictive materials

Giant self-biased converse magnetoelectric (CME) effects with obvious hysteretic behaviors are systematically investigated in two-phase SmFe2/PZT [Pb(Zr1−x, Tix)O3] multiferroic laminates at room temperature. Taking advantage of the huge anisotropic field of SmFe2 plate, large remnant CME coupling is provoked by this field instead of permanent magnets to bias the laminate. Consequently, bitable magnetization status switching is realized through a smaller ac voltage far below the electric coercive field in the absence of magnetic bias field. Experiments demonstrate that a large remnant CME coefficient (αCME) of 0.007 mG/V is achieved, exhibiting ∼50 times higher CME coefficient than the previous laminate composite multi-phase magnetostrictive plates. These results provide promising applications for realization of high-density magnetoelectric random access memories (MERAMs) devices with lower energy consumption.

Giant magnetoelectric effect in nonlinear Metglas/PIN-PMN-PT multiferroic heterostructure

In this paper, we demonstrate high converse magnetoelectric (ME) coupling in a Metglas/Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) laminated ME composite by exploiting stress and field induced reversible ferroelectric-ferroelectric phase transitions in a relaxor ferroelectric single crystal. The approach exploits large transformational strain induced by low applied electric field in a PIN-PMN-PT crystal that was mechanically stressed close to a rhombohedral to orthorhombic phase transformation. The ME coefficient was enhanced by an order of magnitude as compared to the linear piezoelectric regime, with a maximum value of 1.3 × 10−7 s m−1 in non-resonant mode. This phenomenon can thus be exploited to provide improvements in the development of ME devices and magnetic sensors.

Studies on magnetoelectric coupling in PFN-NZFO composite at room temperature

We report magnetoelectric coupling and Raman spectroscopic studies on [(1 − x)Pb(Fe0.5Nb0.5)O3-xNi0.65Zn0.35Fe2O4] (x = 0.20) PFN-NZFO composite. Apart from the presence of zone centre Raman active modes of the parent compound, some new peaks are observed in the low frequency region. The electric field controlled peak position (∼48 cm−1) suggests that this mode is of magnetic origin. From temperature dependent Raman scattering studies, temperature coefficients for phonons of different symmetries were estimated. Our measurements on electrical control of magnetic order and magnetic control of electrical order confirmed the existence of converse and direct magnetoelectric coupling in this composite at room temperature.

Film size-dependent voltage-modulated magnetism in multiferroic heterostructures.

The electric-voltage-modulated magnetism in multiferroic heterostructures, also known as the converse magnetoelectric (ME) coupling, has drawn increasing research interest recently owing to its great potential applications in future low-power, high-speed electronic and/or spintronic devices, such as magnetic memory and computer logic. In this article, based on combined theoretical analysis and experimental demonstration, we investigate the film size dependence of such converse ME coupling in multiferroic magnetic/ferroelectric heterostructures, as well as exploring the interaction between two relating coupling mechanisms that are the interfacial strain and possibly the charge effects. We also briefly discuss some issues for the next step and describe new device prototypes that can be enabled by this technology.

Electric-field induced strain modulation of magnetization in Fe-Ga/Pb(Mg1/3Nb2/3)-PbTiO3 magnetoelectric heterostructures

Magnetostrictive Fe-Ga thin layers were deposited on ⟨110⟩-oriented Pb(Mg1/3Nb2/3)-30%PbTiO3 (PMN-30%PT) substrates by pulsed laser deposition. The as-prepared heterostructures showed columnar arrays aligned in the out-of-plane direction. Transmission electron microscopy revealed nanocrystalline regions within the columnar arrays of the Fe-Ga film. The heterostructure exhibited a strong converse magnetoelectric coupling effect of up to 4.55 × 10−7 s m−1, as well as an electric field tunability of the in-plane magnetic anisotropy. Furthermore, the remanent magnetization states of the Fe-Ga films can be reversibly and irreversibly changed by external electric fields, suggesting a promising and robust application in magnetic random access memories and spintronics.

Large E-field tunability of microwave ferromagnetic properties in Fe59.3Co28.0Hf12.7/PZN-PT multiferroic composites

Strong converse magnetoelectric coupling was observed in a multiferroic heterostructure of Fe59.3Co28.0Hf12.7 film on (011) cut lead zinc niobate-lead titanate (PZN-PT) slab, which exhibited a large electric field (E-field) tunability of microwave magnetic properties. With the increase of E-field from 0 to 6 kV/cm on PZN-PT, the ferromagnetic resonance (FMR) field Hr shifts downwards by 430.7 Oe along [011¯] direction and upwards by 492.9 Oe along [100] direction of the PZN-PT. Accordingly, the strong magnetoelectric coupling led to a significantly enhanced self-biased FMR frequency from 4.2 to 7.9 GHz under zero bias magnetic field, and the magnetic damping constant α was decreased from 0.0260 to 0.0185 at the same time. These features demonstrate that this multiferroic laminate is promising in fabrication of E-field tunable microwave components.

Evaluating the electro-optical effect in alternating current-voltage-modulated Kerr response for multiferroic heterostructures

Voltage-modified Kerr magnetometer has been widely used to measure the voltage-modulated magnetic properties in multiferroic magnetic/ferroelectric heterostructures, where the Kerr signal change is considered to be in proportion to magnetization change, i.e., the magneto-optical Kerr effect. However, the total Kerr signal changes might also incorporate contribution from the electro-optical effect of the ferroelectric layer in the multiferroic heterostructure. Here, we evaluate quantitatively, by combining analytical calculations with experimental observations, such electro-optical contribution in the total voltage-induced Kerr signal changes with comparison to those from Kerr effect via converse magnetoelectric coupling. Influences of several parameters, including the magnetic film thickness on the Kerr signal changes, are also investigated.

Converse magnetoelectric coupling in NiFe/Pb(Mg1/3Nb2/3)O3–PbTiO3 nanocomposite thin films grown on Si substrates

Multiferroic NiFe (∼30 nm)/Pb(Mg1/3Nb2/3)O3–PbTiO3(PMN–PT, ∼220 nm) bilayered thin films were grown on common Pt/Ti/SiO2/Si substrates by a combination of off-axis magnetron sputtering and sol-gel spin-coating technique. By using AC-mode magneto-optical Kerr effect technique, the change in the Kerr signal (magnetization) of the NiFe upon applying a low-frequency AC voltage to the PMN–PT film was in situ acquired at zero magnetic field. The obtained Kerr signal versus voltage loop essentially tracks the electromechanical strain curve of the PMN–PT thin film, clearly demonstrating a strain-mediated converse magnetoelectric coupling, i.e., voltage-modulated magnetization, in the NiFe/PMN–PT nanocomposite thin films.

Inequivalence of direct and converse magnetoelectric coupling at electromechanical resonance

Resonant direct and converse magnetoelectric (ME) effects have been investigated experimentally and theoretically in FeGa/PZT/FeGa sandwich laminate composites under the same electric and magnetic bias conditions. Resonant direct ME effect (DME) occurs at antiresonance frequency while resonant converse ME effect (CME) occurs at resonance frequency. The antiresonance and resonance frequencies have close but different values under identical bias conditions. The magnitudes of resonant effective ME coefficients for direct and converse ME effects are also not equal. A model was developed to describe the frequency response of DME and CME in laminate composite, which was in good agreement with experimental results.

ChemInform Abstract: Voltage Control of Magnetism in Multiferroic Heterostructures and Devices

AbstractReview: 210 refs.

Large E-field tunability of microwave ferromagnetic properties in Fe50Co50-Hf/lead zinc niobate–lead titanate multiferroic laminates

Fe50Co50-Hf films were deposited on the (011)-cut single crystal lead zinc niobate–lead titanate (PZN-PT) substrates by a composition gradient sputtering (CGS) method. Strong converse magnetoelectric (ME) coupling was observed in the multiferroic laminates of CGS Fe50Co50-Hf/PZN-PT, which exhibited a large electric field (E-field) tunability of microwave magnetic properties. With the increase of E-field strength from 0 to 8 kV/cm, the ferromagnetic resonance (FMR) fields Hr shifted upwards by 270.2 Oe and downwards by 237.7 Oe along hard axis and easy axis directions, being equivalent to 33.8 and 29.7 Oe cm/kV, respectively. Accordingly, the self-biased ferromagnetic resonance frequency fFMR significantly enhanced from 4.0 to 6.5 GHz with an increment of ΔfFMR = 2.5 GHz under a zero-bias magnetic field, and the magnetic damping constant α decreases from 0.0280 to 0.0185. The strong ME coupling between CGS Fe50Co50-Hf film and PZN-PT substrate not only enhanced the fFMR but also reduced the magnetic loss at microwave frequencies, which gives great opportunity in fabrication of tunable microwave devices.

VOLTAGE CONTROL OF MAGNETISM IN MULTIFERROIC HETEROSTRUCTURES AND DEVICES

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.

Low moment NiCr radio frequency magnetic films for multiferroic heterostructures with strong magnetoelectric coupling

Magnetic/piezoelectric multiferroic heterostructures with a magnetic thin film on a piezoelectric slab provides a great opportunity to achieve a strong converse magnetoelectric coupling with great potential for voltage tunable magnetic devices. Efforts have been made in developing highly magnetostrictive RF magnetic materials with low magnetization using magnetic/piezoelectric heterostructures to generate large electric-field induced effective magnetic fields. In this work, we report on NiCr films having low magnetization and relatively large magnetostriction. Strong converse magnetoelectric coupling and large electric field tunable ferromagnetic resonance (FMR) bandwidths are achieved in layered NiCr/lead zirconate titanate (PZT) and NiCr/lead zinc niobate lead titanate (PZN-PT) multiferroic heterostructures. A large electric field induced effective magnetic field of 260 Oe for NiCr/PZT and 756 Oe for NiCr/PZN-PT was observed, corresponding to a giant magnetoelectric coupling coefficient of 13 Oe cm/kV in NiCr/PZT and 75.6 Oe cm/kV in NiCr/PZN-PT multiferroic heterostructures. A high voltage tunable FMR frequency range was observed, with fmax/fmin being 124 and 325% for NiCr/PZT and NiCr/PZN-PT. The strong converse magnetoelectric coupling of NiCr/PZT and NiCr/PZN-PT heterostructures provide great opportunities for electric field tunable RF magnetic devices.

A simple method for direct observation of the converse magnetoelectric effect in magnetic/ferroelectric composite thin films

A novel characterization method is presented to directly observe the pure converse magnetoelectric (ME) effect, i.e., the electric-field modification of magnetization, in composite magnetic/ferroelectric (FE) layered thin films. A low-frequency AC electric-voltage, rather than DC voltage bias, is applied to the FE thin films to minimize the leakage current, whereby the possible side effect of heating can be avoided. In particular, by synchronizing the frequency of the Kerr signal detector to the AC actuation voltage bias, the voltage-induced change of the magnetization in the magnetic films can be in situ recorded even under zero external magnetic fields. For illustration, this method is applied to two similar magnetic/FE composite thin films, with significant strain-mediated converse ME coupling being demonstrated in both cases.

Controlling voltage step-up ratio of Rosen-type transformer based on magnetoelectric coupling

We proposed a magnetoelectric (ME) composite transformer by bonding a Rosen-type transformer and a Terfenol-D plate, whose voltage step-up ratio could be controlled by an applied magnetic field. When applying a sine signal on the input port of the transformer, an amplifying signal was produced at the output port because of the amplifying effect. Meanwhile, a magnetization was induced in the magnetostrictive part due to the converse ME coupling, and then a voltage at the output port due to the direct ME effect. Superimposition of the ME signal on the amplifying signal resulted that the voltage step-up ratio of the composite transformer could be controlled by the applied magnetic field. In addition, electric-field-induced magnetization in Terfenol-D is very strong, which was dominated by the stress in the composite transformer.

Large converse magnetoelectric coupling effect at room temperature in CoPd/PMN-PT (001) heterostructure

We report a large converse magnetoelectric (CME) effect at room temperature in a multiferroic heterostructure formed from thin layers of perpendicularly magnetized CoxPd1-x alloys deposited on a piezoelectric single-crystal of lead magnesium niobate-lead titanate PMN-PT(001). The CME results from a strain-induced reorientation of the CoPd magnetization. By varying the composition and thickness of the CoxPd1-x film, a large converse magnetoelectric coupling constant, α=8×10−7 s/m, at room temperature was found for 10 nm Co0.25Pd0.75. This large CME effect results from combining a highly magnetostrictive CoPd alloy with highly piezoelectric PMN-PT.

Electrically controlled magnetization switching in a multiferroic heterostructure

A demonstration of magnetization reversal via the application of electric field across a multiferroic heterostructure, consisting of a FeCoV ribbon bonded to a lead magnesium niobate-lead titanate crystal, is presented. The magnetization switching occurs by an abrupt change in magnetization near ferromagnetic coercivity, coinciding with an electrical field-induced magnetic anisotropy field. Experiments reveal a converse magnetoelectric coupling of α=μ0(dM/dE)=1.6×10−7 s m−1 upon magnetization reversal in the strain-mediated heterostructure. The frequency dependence of magnetization switching is presented and explained within the framework of a relaxation model for the multiferroic heterostructure.

Dynamic response of converse magnetoelectric effect in a PMN-PT-based multiferroic heterostructure

A multiferroic heterostructure, consisting of a 25 μm thick Metglas® ribbon affixed to a lead magnesium niobate–lead titanate (PMN-PT) crystal, was systemically studied to investigate the time response of converse magnetoelectric coupling under the application of electric fields at low frequencies (0.05<f<10 Hz). This multiferroic heterostructure exhibits a considerably strong converse magnetoelectric effect, CME=−80%, where CME=[M(E)−M(0)]/M(0), and a converse ME coupling constant, A=22.5 Oe-cm/kV, at frequencies below 1 Hz and near saturation electric polarization. A switching time (t s), representing the response time of the CME coupling, is measured to be 0.6 seconds for this heterostructure under the application of instantaneous electric fields. The switching time results in significant influences on the magnetoelectric effect especially at frequencies higher than 2 Hz. The dynamic response of CME coupling is predominantly determined by ferroelectric relaxation within the PMN-PT crystal, as opposed to the magnetic relaxation of the Metglas® ribbon. A model was used to describe the dynamic behavior of CME coupling in disordered systems such as PMN-PT.

Electric field controlled magnetic hysteresis loops in a Metglas®/PMN–PT heterostructure

An electric field tunable magnetic hysteresis loop was studied in a multiferroic heterostructure consisting of a 25 µm thick Metglas® ribbon affixed to a lead magnesium niobate–lead titanate (PMN–PT) crystal. This multiferroic heterostructure exhibits a considerably strong converse magnetoelectric effect, CME = −80%, where CME = [M(E) − M(0)]/M(0), and a converse magnetoelectric coupling constant, A = 23 Oe cm kV−1, in the vicinity of the saturation electric polarization. This work systematically demonstrates the tunability of magnetic parameters including magnetization, coercivity, remanence and squareness, under the application of an electric field of 0–8 kV cm−1. Additionally, the physical mechanism of the CME is discussed. These results provide useful resources for the design of a new generation of electrically controlled devices.

Converse magnetoelectric effects in a galfenol and lead zirconate titanate bilayer

Polycrystalline samples of galfenol Fe1−xGax (x=0.17–0.3) have been prepared and used in a bilayer with lead zirconate titanate for studies on the magnetoelectric (ME) effect. The converse ME effect which is the magnetic response of the sample to an applied ac electric field has been investigated. Piezoelectric deformations due the electric field result in an induced magnetization in galfenol that is measured as a voltage U in a pick-up coil wound on the bilayer. A resonance enhancement in the magnitude of U is evident for bending oscillations and longitudinal acoustic oscillations in the bilayer. Data on U as a function of the strength and orientation of bias field H show a maximum in ME coupling strength for in-plane component of H≈250Oe. The data have been analyzed in terms of H dependence of the magnetostriction for galfenol. The converse ME coupling is strong enough for use of the bilayer as a sensor of magnetic and electric fields.