Large Magnetoelectric Coupling Research Articles

Ferromagnetic resonance manipulation by electric fields in Ni81Fe19/Bi3.15Nd0.85Ti2.99Mn0.01O12 multiferroic heterostructures

We investigated electric-field modulation of ferromagnetic resonance (FMR) in Ni81Fe19 (NiFe)/Bi3.15Nd0.85Ti2.99Mn0.01O12 (BNTM) heterostructures at room temperature. BNTM thin films were deposited on a Pt (111)/Ti/SiO2/Si (100) substrate by the sol-gel method. The strain effect is produced by the electric field applied to the BNTM layer, which results in the FMR spectrum shift by tuning of the magnetic anisotropy of the NiFe microstrip devices. A strain-induced magnetic anisotropy change of 332 fJ/Vm is obtained by analyzing the experimental FMR spectra. We discussed an influence on spin orbit torques by applying an electric field to a ferroelectric (FE) layer via coupling to polarization with FMR experiments evidencing. The torque ratios τa/τb increased at first and then declined from the positive to negative electric field. As the value of the applied electric field changes from 129 kV/cm to 0 kV/cm, the variation of the torque ratios τa/τb (the field-like torque τa and damping-like torque τb) is about 0.07. Our results reported in this work demonstrate a route to realize a large magneto-electric coupling effect at room temperature and provide some insights into possible applications of the ferromagnetic/FE device.

The magnetoelectric effect of the CFO thin film by coupling a P(VDF-co-TrFE) piezoelectric layer

The CoFe2O4 (CFO) thin films are prepared by the sol-gel method combined with the spin-casting process, and the related SEM and XRD results show that a 9-layer spinning of the original sol together with an annealing temperature of 700 °C is the appropriate condition for obtaining this CFO film with an excellent magnetic performance. The CFO films are subsequently compounded with a ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-co-TrFE)]. After polarizing the obtained CFO/P(VDF-co-TrFE) double-layer composite film under a high electrical field of 275 MV/m, the P(VDF-co-TrFE) layer shows the character of normal ferroelectricity that has a large dielectric permittivity (ɛ33/ɛ0 = 9.5) and a high piezoelectric value (d31 = 20 pC/N). Interestingly, we also find that the magnetization of this electrically poled CFO/P(VDF-co-TrFE) film increases from 85.58 to 99.15 emu/cm3 at a magnetic field of 1.8 T since the electrostrictive effect may lead to the re-orientation of magnetic domains and thereby resulting in a magnetization easy-axis reorientation effect in the out-of-plane direction of the CFO thin film. Consequently, a large magnetoelectric coupling coefficient (αE31) of 508.5 MV/cm Oe is obtained through calculation provided the interfaces between CFO and P(VDF-co-TrFE) have an appropriate compatible coefficient of about 0.5. The results indicate that the CFO/P(VDF-co-TrFE) double-layer film is a potential multiferroic composite as an attractive candidate for memory storage and spintronic devices.

Voltage control of perpendicular magnetic anisotropy in (Co/Pt)3/Pb(Zn1/3Nb2/3)O3-PbTiO3 multiferroic heterostructures at room temperature

Voltage control of perpendicular magnetic anisotropy (PMA) in ferromagnetic/ferroelectric multiferroic heterostructures is a promising method to enable high density and low power perpendicular magnetic information storage. In this study, we successfully achieved large voltage tuning of PMA at room temperature in (Co/Pt)3/Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) multiferroic heterostructures. Voltage tuning of magnetic anisotropy and the magnetoelectric coupling effect has been qualitatively studied by ferromagnetic resonance, and the multiferroic heterostructure could be reversibly flipped between two distinct PMA states under zero or high electric fields. During the linear piezo-strain response of PZN-PT, the multiferroic heterostructures exhibit small magnetoelectric coupling and the electric field-induced magnetic anisotropy field was about 295 Oe. During the electric field-induced phase transition of PZN-PT, voltage tuning of PMA enhanced more than two times that of the first linear region and the electric field-induced magnetic anisotropy field increased to 634 Oe. Finally, this magnetoelectric coupling was enhanced to 672 Oe by applying 12 kV/cm, corresponding to a large magnetoelectric coupling coefficient up to 56 Oe·cm/kV. Benefiting from the giant strain response during voltage-induced phase transition in PZN-PT, voltage tuning of PMA in those multiferroic heterostructures is a promising candidate for power-efficient magnetic memories.

Voltage control of magnetism in NiZn ferrite/mica/PMNPT heterostructure with giant tunability and narrow linewidth

Recently, large magnetoelectric coupling of a spinel/piezoelectric heterostructure has been reported. However, the linewidth of the spinel is very large due to lattice mismatch when ferrite is directly deposited on piezoelectric substrates. This indicates a large magnetic loss, which impedes the spinel/piezoelectric heterostructure from useful device applications. Mica is a well-known 2D material, which can be split manually layer by layer without the substrate clamping effect. In this report, NiZn ferrite was deposited on a mica substrate by a spin-spray deposition technique. Spin-spray deposition is a wet chemical synthesis technique involving several chemical reactions for generating high-quality crystalline spinel ferrite films with various compositions directly from an aqueous solution. The thickness of ferrite is 2 μm, and the linewidth of the ferromagnetic resonance (FMR) is 115 Oe which is suitable for RF/microwave devices. The large FMR field tuning of 605 Oe was observed in NiZn ferrite/mica/PMN-PT heterostructures with minimal substrate clamping effect by reducing the thickness of the mica substrate. These multiferroic heterostructures exhibiting combined giant magnetoelectric coupling and narrow ferromagnetic resonance linewidth offer great opportunities for flexible RF magnetic devices.

Thermal Driven Giant Spin Dynamics at Three-Dimensional Heteroepitaxial Interface in Ni0.5Zn0.5Fe2O4/BaTiO3-Pillar Nanocomposites

Traditional magnetostrictive/piezoelectric laminated composites rely on the two-dimensional interface that transfers stress/strain to achieve the large magnetoelectric (ME) coupling, nevertheless, they suffer from the theoretical limitation of the strain effect and of the substrate clamping effect in real ME applications. In this work, 3D NZFO/BTO-pillar nanocomposite films were grown on SrTiO3 by template-assisted pulsed laser deposition, where BaTiO3 (BTO) nanopillars appeared in an array with distinct phase transitions as the cores were covered by NiZn ferrite (NZFO) layer. The perfect 3D heteroepitaxial interface between BTO and NZFO phases can be identified without any edge dislocations, which allows effective strain transfer at the 3D interface. The 3D structure nanocomposites enable the strong two magnon scattering (TMS) effect that enhances ME coupling at the interface and reduces the clamping effect by strain relaxation. Thereby, a large FMR field shift of 1866 Oe in NZFO/BTO-pillar nanocomposite was obtained at the TMS critical angle near the BTO nanopillars phase transition of 255 K.

Magnetic structure driven ferroelectricity and large magnetoelectric coupling in antiferromagnet Co4Nb2O9

Synthesis and extensive structural, pyroelectric, magnetic, dielectric and magneto-electric characterizations are reported for polycrystalline Co4Nb2O9 towards unraveling the multiferroic ground state. Magnetic measurements confirm that Co4Nb2O9 becomes an anti-ferromagnet at around 28 K. Associated with the magnetic phase transition, a sharp peak in pyroelectric current indicates the appearance of strong magneto-electric coupling below Neel temperature (TN) along with large coupling constant upto 17.8 μC/m2T. Using temperature oscillation technique, we establish Co4Nb2O9 to be a genuine multiferroic with spontaneous electric polarization in the anti-ferromagnetic state in the absence of magnetic field poling. This is in agreement with our low temperature neutron diffraction studies that show the magnetic structure of Co4Nb2O9 to be that of a non-collinear anti-ferromagnet with ferroelectric ground state.

Hybrid improper ferroelectricity and multiferroic in Ruddlesden-Popper structures

Hybrid improper ferroelectricity (HIF) is a secondary ferroelectric ordering induced by the coupling between oxygen octahedral in-plane rotation and out-of-plane tilt in a metal-oxide containing the perovskite structure units. Investigation of HIF will greatly extend the connotation and denotation of ferroelectric physics and material science, and it is expected to develop the room temperature single phase multiferroic material with large polarization and strong magnetoelectric coupling, owing to its intrinsic characteristic of the electric-field control of magnetism through HIF in magnet. In the present paper, the recent primary progress of HIFs and the multiferroics with Ruddlesden-Popper structures is reviewed, and the perspective of the future development is also presented.

Progress of converse magnetoelectric coupling effect in multiferroic heterostructures

Electric-field control of magnetism has recently received much attention because of low-power consumption, which has potential applications in low-power multifunction devices. Ferromagnetic/ferroelectric multiferroic heterostructure is a useful way to realize the electric-field control of magnetism. Strain-mediated magnetoelectric coupling with large magnetoelectric coupling coefficient at room temperature is one of the current research hotspot. In this paper, we give an overview of recent progress of strain-mediated magnetoelectric coupling in multiferroic heterostructures.This review paper consists of five parts:introduction of multiferroics, electric-field control of magnetism in multiferroic heterostructures, electrical control of magnetization reversal, electric-field control of magnetic tunnel junctions, and the future prospects of multiferroic heterostructures. The basic concepts of multiferroics and background of magnetoelectric coupling effect are introduced in the first part.In the second part, a brief review of the recent work on the Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) based multiferroic heterostructures is given. The PMN-PT has a FE domain structure, which plays a vital role in electric-field control of magnetism, especially the 109 domain switching. For PMN-PT (001), the importance of 109 domain switching on the nonvolatile electrical control of magnetism is discussed. For PMN-PT (011), it is shown how to obtain nonvolatile strain which induces magnetic easy axis to be rotated by 90. The work on electric-field modulation of ferromagnetic material with perpendicular magnetic anisotropy is also mentioned.Electric-field control of magnetization reversal is still a challenge and remains elusive. Combination of strain-mediated magnetoelectric coupling and exchanging bias is a promising method to reverse magnetization by electric field, and the exchange-biased system/ferroelectric structures are given in the third part. There are also some theoretical attempts and proposals to realize the electrical control of 180 magnetization reversal. Then the method to manipulate magnetic tunnel junctions by electric field is given through integrating multiferroics and spintronics. Further outlook of the multiferroic heterostructures is also presented finally.

Ferroelectric Phase Transition Induced a Large FMR Tuning in Self-Assembled BaTiO3:Y3Fe5O12 Multiferroic Composites.

Yttrium iron garnet (YIG) is of great importance in RF/microwave devices for its low loss, low intrinsic damping, and high permeability. Nevertheless, tuning of YIG-based multiferroics is still a challenge due to its near-zero magnetostriction and the difficulty of building epitaxial interface between ferromagnetic garnet and ferroelectric perovskite phases. In this work, the vertically aligned heterostructure of YIG:BTO/STO(001) with local epitaxial interface between BTO and YIG is well-constructed, where the single crystal BTO pillars are embedded in YIG matrix. A large magnetoelectric coupling effect that drives YIG's FMR shift up to 512 and 333 Oe (1-2 order greater than those of all state-of-the-art progresses) is obtained through BTO ferroelectric phase changes induced by temperature variation at 295 and 193 K, correspondingly. This record high magnetoelectric tunability of YIG paves a way toward thermal/electrical tunable YIG devices.

Strain-Mediated Coexistence of Volatile and Nonvolatile Converse Magnetoelectric Effects in Fe/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 Heterostructure.

Strain-mediated ferromagnetic/ferroelectric (FE) heterostructures have played an important role in multiferroic materials to investigate the electric-field control of magnetism in the past decade, due to their excellent performances, such as room-temperature operation and large magnetoelectric (ME) coupling effect. Because of the different FE-switching-originated strain behaviors and varied interfacial coupling effect, both loop-like (nonvolatile) and butterfly-like (volatile) converse ME effects have been reported. Here, we investigate the electric-field control of magnetism in a multiferroic heterostructure composed of a polycrystalline Fe thin film and a Pb(Mg1/3Nb2/3)0.7Ti0.3O3 single crystal, and the experimental results exhibit complex behaviors, suggesting the coexistence of volatile and nonvolatile converse ME effects. By separating the symmetrical and antisymmetrical parts of the electrical modulation of magnetization, we distinguished the loop-like hysteresis and butterfly-like magnetization changes tuned by electric fields, corresponding to the strain effects related to the FE 109° switching and 71/180° switching, respectively. Further magnetic-field-dependent as well as angular-dependent investigation of the converse ME effect confirmed the strain-mediated magnetism involving competition among the Zeeman energy, magnetocrystalline anisotropy energy, and strain-generated magnetoelastic energy. This study is helpful for understanding the electric-field control of magnetism in multiferroic heterostructures as well as its relevant applications.

Interrelation between domain structures and polarization switching in hybrid improper ferroelectric Ca3(Mn,Ti)2O7

Ca3Mn2O7 and Ca3Ti2O7 have been proposed as the prototypical hybrid improper ferroelectrics (HIFs), and a significant magnetoelectric (ME) coupling in magnetic Ca3Mn2O7 is, in fact, reported theoretically and experimentally. Although the switchability of polarization is confirmed in Ca3Ti2O7 and other non-magnetic HIFs, there is no report of switchable polarization in the isostructural Ca3Mn2O7. We constructed the phase diagram of Ca3Mn2-xTixO7 through our systematic study of a series of single crystalline Ca3Mn2-xTixO7 (x = 0, 0.1, 1, 1.5, and 2). Using transmission electron microscopy, we have unveiled the unique domain structure of Ca3Mn2O7: the high-density 90° stacking of a- and b-domains along the c-axis due to the phase transition through an intermediate Acca phase and the in-plane irregular wavy ferroelastic twin domains. The interrelation between domain structures and physical properties is unprecedented: the stacking along the c-axis prevents the switching of polarization and causes the irregular in-plane ferroelastic domain pattern. In addition, we have determined the magnetic phase diagram and found complex magnetism of Ca3Mn2O7 with isotropic canted moments. These results lead to negligible observable ME coupling in Ca3Mn2O7 and guide us to explore multiferroics with large ME coupling.

A Generalizable Multigram Synthesis and Mechanistic Investigation of YMnO3 Nanoplates

The reproducible gram-scale synthesis of crystalline nanoscale multiferroics is critical for the development of the next generation of commercially relevant electronic devices. Of the subset of multiferroic materials, yttrium manganese oxide (YMnO3) is highly attractive, because of its large magneto-electric coupling constants and the recent observation of giant polarization under pressure in these types of rare earth manganites. Utilizing a unique synthetic methodology that combines metal–oleate thermal degradation with the use of a molten salt protocol, we were able to reproducibly generate monodisperse distributions of morphologically distinctive yttrium manganese oxides. Specifically, using a molten NaCl flux, we were able to synthesize phase-pure, single-crystalline hexagonal YMnO3 nanoplates, measuring 441 ± 241 nm in diameter and 46 ± 6 nm in height. Moreover, these nanoplates gave rise to multiferroic behavior, which was confirmed by the observation of a ferroelectric phase from a combination of h...

Room temperature large self-biased magnetoelectric effect in non-lead based piezoelectric and magnetostrictive (0−3) particulate composite system

In this work, room temperature magnetoelectric properties of (0−3) particulate composites of non lead based piezoelectric BNTKNNLTS [0.97(Bi0.5Na0.5TiO3)–0.03(K0.47Na0.47Li0.06Nb0.74Sb0.06Ta0.2O3) and magnetostrictive CZFMO (Co0.6Zn0.4Fe1.7Mn0.3O4) are presented. Composite samples of (1-x)(BNTKNNLTS)-x(CZFMO), with x=0.1 and 0.5, are synthesized by solid state reaction route. X-ray diffraction confirms the single phase formation of parent phases and the presence of two phases in the composites. Similar sintering conditions of the two individual components lead to optimal ferroelectric and ferromagnetic properties in the composites. A large self-biased magnetoelectric (ME) coupling ~74mV/cm.Oe for the sample with x=0.1 (measured in longitudinally magnetized-transversely polarized configuration) is observed at room temperature.

Reversible strain control of magnetic anisotropy in magnetoelectric heterostructures at room temperature.

The ability to tune both magnetic and electric properties in magnetoelectric (ME) composite heterostructures is crucial for multiple transduction applications including energy harvesting or magnetic field sensing, or other transduction devices. While large ME coupling achieved through interfacial strain-induced rotation of magnetic anisotropy in magnetostrictive/piezoelectric multiferroic heterostructures has been demonstrated, there are presently certain restrictions for achieving a full control of magnetism in an extensive operational dynamic range, limiting practical realization of this effect. Here, we demonstrate the possibility of generating substantial reversible anisotropy changes through induced interfacial strains driven by applied electric fields in magnetostrictive thin films deposited on (0 1 1)-oriented domain-engineered ternary relaxor ferroelectric single crystals with extended temperature and voltage ranges as compared to binary relaxors. We show, through a combination of angular magnetization and magneto-optical domain imaging measurements, that a 90° in-plane rotation of the magnetic anisotropy and propagation of magnetic domains with low applied electric fields under zero electric field bias are realized. To our knowledge, the present value attained for converse magnetoelectric coupling coefficient is the highest achieved in the linear piezoelectric regime and expected to be stable for a wide temperature range, thus representing a step towards practical ME transduction devices.

Strain-controlled interfacial magnetization and orbital splitting in La2/3Sr1/3MnO3/tetragonal BiFeO3 heterostructures

The electronic and magnetic properties of La2/3Sr1/3MnO3(LSMO)/tetragonal BiFeO3(BFO) heterostructures with the xy-plane biaxial strain were investigated by first-principles calculations. As the xy-plane lattice constant is ranging from 3.619 to 3.921 Å, a large interfacial magnetoelectric coupling (IMEC) appears in the LaO/Fe-O2 and LaO/O2-Fe models. Particularly, the interfacial Mn in the LaO/O2-Fe model shows a large spin-down t2g orbital splitting at a strain from −2% to 6%, where the maximum splitting energy is 283 meV at 2%. Additionally, the LaO/O2-Fe model is half-metallic at a strain of 2%, 4%, and 6%. The results demonstrate that IMEC, orbital occupancy, and half-metallicity of LSMO/BFO heterostructures can be effectively engineered by the interfacial coupling and in-plane strain, which paves a way for designing the novel magnetoelectric devices.

Colossal magnetodielectric effect and spin flop in magnetoelectric Co4Nb2O9 crystal

We have investigated the detailed magnetic, magnetoelectric (ME), magnetodielectric (MD) and thermal expansion properties in Co4Nb2O9 crystal. A magnetic-field-induced spin flop was observed below antiferromagnetic (AFM) transition temperature TN. Dielectric constant at applied magnetic field nearly diverges around the AFM transition, giving rise to a colossal MD effect as high as ∼138% around TN. Theoretical analysis of the ME and MD data revealed a major contribution of critical spin fluctuation to the colossal MD effect in Co4Nb2O9. These results suggest that linear ME materials with large ME coupling might be potentially used to realize large MD effect for future application.

Evidence of multiferroicity inNdMn2O5

Recently, $R{\text{Mn}}_{2}{\text{O}}_{5}$ ($R=\text{rare}$ earth, $\text{Bi}, \text{Y}$) type multiferroics have drawn considerable attention, because of magnetically induced ferroelectricity along with an extremely large magnetoelectric coupling. Here, we present a detailed study on ${\text{NdMn}}_{2}{\text{O}}_{5}$ which is a crucial composition between the nonferroelectric ${\text{PrMn}}_{2}{\text{O}}_{5}$ and ferroelectric ${\text{SmMn}}_{2}{\text{O}}_{5}$. We report the results of heat capacity, magnetization, dielectric permittivity, and electric polarization measurements along with an accurate description of the structural and microscopic magnetic properties obtained from high resolution x-ray and neutron diffraction studies. We show that ${\text{NdMn}}_{2}{\text{O}}_{5}$ is ferroelectric, although the magnitude of polarization is much weaker than that of the other multiferroic members. The direction of the polarization is along the crystallographic $b$ axis and its magnitude can be tuned with the application of a magnetic field. Moreover, unlike the other multiferroic members of this series, ferroelectricity in ${\text{NdMn}}_{2}{\text{O}}_{5}$ emerges in an incommensurate magnetic state. The present study also provides evidence in support of the influence of the rare-earth size on the magnetoelectric phase diagram.

Multiferroic Clusters: A New Perspective for Relaxor‐Type Room‐Temperature Multiferroics

Multiferroics are promising for sensor and memory applications, but despite all efforts invested in their research no single‐phase material displaying both ferroelectricity and large magnetization at room‐temperature has hitherto been reported. This situation has substantially been improved in the novel relaxor ferroelectric single‐phase (BiFe0.9Co0.1O3)0.4–(Bi1/2K1/2TiO3)0.6, where polar nanoregions (PNR) transform into static‐PNR as evidenced by piezoresponse force microscopy (PFM) and simultaneously enable congruent multiferroic clusters (MFC) to emerge from inherent strongly magnetic Bi(Fe,Co)O3 rich regions as verified by magnetic force microscopy (MFM) and secondary ion mass spectrometry. The material's exceptionally large Néel temperature TN = 670 ± 10 K, as found by neutron diffraction, is proposed to be a consequence of ferrimagnetic order in MFC. On these MFC, exceptionally large direct and converse magnetoelectric (ME) coupling coefficients, α ≈ 1.0 × 10−5 s m−1 at room‐temperature, are measured by PFM and MFM, respectively. It is expected that the non‐ergodic relaxor properties which are governed by the Bi1/2K1/2TiO3 component to play a vital role in the strong ME coupling, by providing an electrically and mechanically flexible environment to MFC. This new class of non‐ergodic relaxor multiferroics bears great potential for applications. Especially the prospect of a ME nanodot storage device seems appealing.

Colossal magnetoelectric effect in 3-1 multiferroic nanocomposites originating from ultrafine nanodomain structures

We investigate colossal magnetoelectric coupling through interactions between ferroelectric and ferromagnetic nanodomains in 3-1 multiferroic BaTiO3/CoFe2O4 nanocomposites using a recent real-space phase field model based on the Landau-Ginzburg theory. A hierarchical ultrafine domain structure is characteristically formed in the nanocomposites, resulting in an extremely high density of domain walls, which causes polarization domains to be more susceptible to an external magnetic field via interfacial strain-mediation. This leads to an anomalously large magnetoelectric coupling effect in the multiferroic nanocomposites. We further demonstrate that the domain configuration and consequent magnetoelectric effect are strongly dependent on the constituent phase distribution, suggesting a promising route for the rational design of multiferroic domains and magnetoelectric effects, reminiscent of recent nano-metamaterial concepts.

Phase separation enhanced magneto-electric coupling in La0.7Ca0.3MnO3/BaTiO3 ultra-thin films.

We study the origin of the magnetoelectric coupling in manganite films on ferroelectric substrates. We find large magnetoelectric coupling in La0.7Ca0.3MnO3/BaTiO3 ultra-thin films in experiments based on the converse magnetoelectric effect. The magnetization changes by around 30–40% upon applying electric fields on the order of 1 kV/cm to the BaTiO3 substrate, corresponding to magnetoelectric coupling constants on the order of α = (2–5)·10−7 s/m. Magnetic anisotropy is also affected by the electric field induced strain, resulting in a considerable reduction of coercive fields. We compare the magnetoelectric effect in pre-poled and unpoled BaTiO3 substrates. Polarized neutron reflectometry reveals a two-layer behavior with a depressed magnetic layer of around 30 Å at the interface. Magnetic force microscopy (MFM) shows a granular magnetic structure of the La0.7Ca0.3MnO3. The magnetic granularity of the La0.7Ca0.3MnO3 film and the robust magnetoelastic coupling at the La0.7Ca0.3MnO3/BaTiO3 interface are at the origin of the large magnetoelectric coupling, which is enhanced by phase separation in the manganite.