Magnetoelectric Composite Films Research Articles

CoFe2O4-BaTiO3 core-shell-embedded flexible polymer composite as an efficient magnetoelectric energy harvester

Flexible magnetoelectric (ME) generators gained immense interest due to the broad applications in wearable and Internet of Things (IoT)-based devices. The key to achieving high energy conversion performance of 0–3 type ME composite films is the prevention of filler aggregation in the polymer matrix and accessing the full potential of intrinsic properties of filler. To achieve high performance, a flexible ME composite film was fabricated by homogeneous distribution of magnetostrictive CoFe2O4-BaTiO3 core-shell (CBCS) fillers into piezoelectric polyvinylidene fluoride (PVDF) polymer. The ME composite film generates an enhanced energy conversion efficiency by optimizing the shell thickness of CBCS and maximizing the electroactive β-phase at the BaTiO3 shell-PVDF interfacial region. The observed ME coefficient of the film reached up to 710 mV/cm∙Oe. Multiphysics simulations based on the finite element analysis were adopted to investigate the role of BaTiO3 shell thickness on the performance of ME film. This study paves the way to achieve higher filler loading content in the ME composite films to develop an efficient, flexible ME generator for eco-friendly permanent power sources.

Enhanced magnetoelectric properties of the composite films of Bi0.5Na0.5Ti0.98Fe0.02O3-δ-NiFe1.98Nd0.02O4 with different deposition sequences

The films of Bi0.5Na0.5Ti1-xFexO3-δ and NiFe2-xNdxO4 were deposited via spin-coating method. The results indicate that the film of Bi0.5Na0.5Ti0.98Fe0.02O3-δ possesses good ferroelectric performance with remnant polarization as high as 25.2 µC·cm−2 and the film of NiFe1.98Nd0.02O4 possesses a maximal saturation magnetization (282.4 emu·cm−3). The composite films of Bi0.5Na0.5Ti0.98Fe0.02O3-δ-NiFe1.98Nd0.02O4 with different deposition sequences were also prepared. In contrast to single-phase films, magnetoelectric composite films exhibit smaller remnant polarization and saturation magnetization. The film of NiFe1.98Nd0.02O4/Bi0.5Na0.5Ti0.98Fe0.02O3-δ (NB) possesses greater values of remnant polarization, saturation magnetization and magnetoelectric coupling coefficient than those for the composite film of Bi0.5Na0.5Ti0.98Fe0.02O3-δ/NiFe1.98Nd0.02O4 (BN). The composite film of BN exhibits greater magnetoelectric coupling coefficients as high as 169.7 mV·cm−1·Oe−1.

Giant Ferroelectric and Piezoelectric Properties of Lead Free Ba0.85Ca0.15Ti0.90Zr0.10O3 Thin Film in 100 nm Thickness Range

Lead‐free Ba0.85Ca0.15Ti0.90Zr0.10O3/SrRuO3 (BCZT/SRO)‐heterostructured thin film grown on (001)‐SrTiO3 substrate is prepared by pulse laser deposition. The microstructure, ferroelectric, and piezoelectric of the thin film are investigated in detail. Giant ferroelectric properties of the BCZT thin films with thickness ≈100 nm and remanent polarization Pr of 57.1 μC cm−2 are obtained, which are attributed to the (00L)‐oriented epitaxial structure and lower substrate clamping. In addition, the BCZT/SRO heterostructure exhibits excellent piezoelectric properties with the d33 values of different grain size (40–140 nm) varied from 75 to 130 pm V−1, providing a potential candidate used as piezoelectric material for magnetoelectric composite films. The BCZT/SRO‐heterostructured thin film with excellent ferroelectric and piezoelectric properties may be a good alternative to Pb(ZrxTi1−x)O3 thin films for piezoelectric device applications.

Enhanced magnetoelectric coupling in novel rare earth metal substituted Sr based Z-hexaferrites/P(VDF-HFP) composites

This research is driven by a desire to create composite films that combine the ferrimagnetic capabilities of pure and La/Nd substituted Sr3Co2Fe24O41 Z-hexaferrites with the multifunctional features of ferroelectric polymers. A flexible magnetoelectric (ME) polymer composite films, with Sr3Co2Fe24O41 (SF), Sr2.85La0.15Co2Fe24O41(SF–La) and Sr2.85Nd0.15Co2Fe24O41 (SF-Nd) as the ferrimagnetic material and poly vinylidene fluoride-hexafluoropropylene (PH) as a ferroelectric component, were synthesized using solution casting method. In the current case, two steps have been used to synthesize ferroelectric and ferrimagnetic composites films: first, SF, SF-La and SF-Nd hexaferrite samples were synthesized using solid state reaction method and then 20% weight percentage of these hexaferrites were incorporated into the PH matrix using solution casting method to form composite film. In order to find the traces of collaborative interactions between the two phases, the structural, magnetic, and ferroelectric properties of these composite samples have been studied. The XRD data confirm the formation of SF, SF-La and SF-Nd hexaferrite dispersed in a piezoelectric copolymer PH matrix. The changes in the ferroelectric properties in different magnetic fields demonstrated the existence of ME coupling in the composite films. The inclusion of PH enhanced the magnetoelectric coupling of composite films. The maximal value of magnetoelectric coupling coefficient (αME) observed is 0.213, 1.227, 3.403 and 9.797 mV cm−1 Oe−1 for SF, PHSF, PHSF-La and PHSF-Nd, respectively. There is approximately 46-time increase in the maximum value of magnetoelectric coupling coefficient (αME) in PHSF-Nd (9.797 mV/cm.Oe) composites as compare to pure SF (0.213 mV/cm.Oe).

Significant magnetoelectric enhancement of composite films of CoZnxFe2-xO4 particles and poly (vinylidene fluoride-trifluoroethylene) for AC magnetic sensors

Polymer-based magnetoelectric (ME) nanocomposites exhibit a low ME effect and high bias field at room temperature, which severely limits their application in flexible wearable sensors. To overcome these obstacles, Zn-doped magnetic nanoparticles of CoZnxFe2-xO4 (x = 0, 0.1, 0.2, and 0.3) were prepared by an auto-combustion method in this work. The obtained magnetostrictive curves imply that Zn element doping can improve greatly the piezomagnetic coefficient of magnetic nanoparticles, and among the tested materials, CoZn0.1Fe1.9O4 has the largest piezomagnetic coefficient. Composite films of poly(vinylidene fluoride-trifluoroethylene) and CoZn0.1Fe1.9O4 (P(VDF-TrFE)/CoZn0.1Fe1.9O4) were prepared by spin coating. The maximum ME voltage coefficient of P(VDF-TrFE)/CoZn0.1Fe1.9O4 composite film with a filler weight concentration of 10 wt% is 87.9 mV cm−1 Oe−1 with a bias field of 1050 Oe and a resonance frequency of 46 kHz, which is the highest value reported in the literature of 0–3 type polymer-based ME composite films at present. To evaluate the composite films for application in magnetic sensors, the ME output voltage was measured at a bias field of 1050 Oe with increasing AC magnetic field, demonstrating a good linear relationship with linearity of 0.999. These results indicate that the piezomagnetic coefficient of magnetic materials is an the important factor for the great enhancement of the ME voltage coefficient. This work provides a new approach for the synthesis of more effective polymer-based ME nanocomposites for potential applications in smart wearables.

Magnetoelectric behavior and magnetic field-tuned energy storage capacity of SrFe12O19 nanofiber reinforced P(VDF-HFP) composite films

• Fabrication of flexible magnetoelectric (ME) P(VDF-HFP)/SrFe 12 O 19 composite films. • Inclusion of SrFe 12 O 19 nanofiber enhances the polar β-phase in P(VDF-HFP) matrix. • P(VDF-HFP)/SrFe 12 O 19 films exhibit enhanced dielectric and ferroelectric properties . • A strong strain mediated ME coupling exists in the P(VDF-HFP)/SrFe 12 O 19 films. • P(VDF-HFP)/SrFe 12 O 19 films' energy storage capacity is tuned by magnetic fields. Flexible, self-standing magnetoelectric (ME) polymer composite films were prepared using the solution casting method by reinforcing one-dimensional ferromagnetic strontium ferrite (SrFe 12 O 19 ) nanofibers, synthesized using the electrospinning method, into poly(vinylidene fluoride–hexafluoropropylene) (P(VDF-HFP)) matrix. The effects of loading of SrFe 12 O 19 nanofibers on the functional, structural, magnetic, dielectric, and ferroelectric properties of P(VDF-HFP) were investigated. The loading enhanced the electroactive β-phase of the films, as confirmed by XRD and FTIR analyses. The ME coupling that existed in the composite films was confirmed by the changes in ferroelectric parameters under various magnetic fields. The energy storage capacity and dielectric constant of the composite films were enhanced with the addition of SrFe 12 O 19 nanofibers, with the maximum values of 56 at 100 Hz and 1678 mJ/cm 3 at 444 kV/cm, respectively, in the composite film with 20 wt% SrFe 12 O 19 nanofibers. The energy storage capacity was further enhanced and tuned by applying an external magnetic field. Thus, this work reports an innovative approach to tuning the energy storage capacity of ME polymer composite films through a magnetic field and also describes use of these films for a wide range of applications, such as energy storage and memory devices and magnetic sensors.

Enhanced multiferroic properties of Bi4Ti3-xCoxO12/La0.67Sr0.33MnO3 layered composite thin films

In this work, Bi4Ti3-xCoxO12/La0.67Sr0.33MnO3 (BITCx/LSMO, x = 0.025, 0.05, 0.10 and 0.15) layered magnetoelectric (ME) composite thin films were successfully synthesized by chemical solution deposition, and the effect of Co2+ doping content on the microstructure, leakage, dielectric property, ferroelectricity, ferromagnetism and ME coupling performance of BITCx/LSMO composite thin films was investigated. Co2+ doping induces improved ferroelectricity and weak ferromagnetism for the BITCx phase. Especially, the single-phase BITC0.05 film exhibits a maximum ME voltage coefficient (αE) of 0.445 mV/cm·Oe at room temperature, suggesting excellent single-phase multiferroic properties. The BITC0.05/LSMO composite thin film possesses the lowest leakage current density, maximum ϵr, minimum tanδ, highest remnant polarization of 24.2 μC/cm2, lowest coercive field of 137 kV/cm and improved saturation magnetization along with a maximum aE value of 27.3 V/cm·Oe. Based on these findings, Co2+-doped Bi4Ti3O12 has excellent single-phase multiferroic properties, and the incorporation of magnetic ion-doped Bi4Ti3O12 with ferromagnetic oxides benefits the improvement of ME composite thin films.

Recent Progress in Devices Based on Magnetoelectric Composite Thin Films.

The strain-driven interfacial coupling between the ferromagnetic and ferroelectric constituents of magnetoelectric (ME) composites makes them potential candidates for novel multifunctional devices. ME composites in the form of thin-film heterostructures show promising applications in miniaturized ME devices. This article reports the recent advancement in ME thin-film devices, such as highly sensitive magnetic field sensors, ME antennas, integrated tunable ME inductors, and ME band-pass filters, is discussed. (Pb1−xZrx)TiO3 (PZT), Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), Aluminium nitride (AlN), and Al1−xScxN are the most commonly used piezoelectric constituents, whereas FeGa, FeGaB, FeCo, FeCoB, and Metglas (FeCoSiB alloy) are the most commonly used magnetostrictive constituents in the thin film ME devices. The ME field sensors offer a limit of detection in the fT/Hz1/2 range at the mechanical resonance frequency. However, below resonance, different frequency conversion techniques with AC magnetic or electric fields or the delta-E effect are used. Noise floors of 1–100 pT/Hz1/2 at 1 Hz were obtained. Acoustically actuated nanomechanical ME antennas operating at a very-high frequency as well as ultra-high frequency (0.1–3 GHz) range, were introduced. The ME antennas were successfully miniaturized by a few orders smaller in size compared to the state-of-the-art conventional antennas. The designed antennas exhibit potential application in biomedical devices and wearable antennas. Integrated tunable inductors and band-pass filters tuned by electric and magnetic field with a wide operating frequency range are also discussed along with miniaturized ME energy harvesters.

Tailored magnetoelectric coupling in magnetically oriented polymer-based iron fiber composite

Artificial multiferroics magnetoelectric (ME) polymer composite films exhibiting collective ferroelectric and magnetic orderings are gaining attractive for the use of flexible ME devices. Herein an anisotropic polymer-based ME composites films is developed, composed of magnetically oriented polycrystalline iron fiber (Fef) and poly(vinylidene fluoride-co-trifluoroethylene) P(VDF–TrFE). The structure, ferroelectric, piezoelectric, magnetic, and ME properties was systematically investigated. Both Fef fillers content and magnetic field direction determined the ME voltage coefficient, magnetical polarization and dielectric response in anisotropic P(VDF-TrFE)–Fef composites. Specifically, the composite with 16% filler loading delivers a peak ME value of 44.5 mV·cm−1·Oe−1 with magnetic field exerted along the fiber axial alignment direction. Such extracted results may encourage a way to optimize flexible composite in anisotropic contactless sensing and detecting applications.

Dielectric Relaxation Behavior of BTO/LSMO Heterojunction.

The BaTiO3 (BTO)/La0.7Sr0.3MnO3 (LSMO) magnetoelectric composite films were prepared by sol-gel method on STO (001) substrates. The heterojunction has highly preferred orientation and exhibits well ferroelectric properties with perfect hysteresis loops and microscopic polarization switch behaviors. The most interesting thing is the abnormal dielectric relaxation phenomenon in the dielectric spectra at high frequency range and around the phase transition temperature of LSMO. By analyzing the resistance properties of LSMO films, it is indicated that charge-based interfacial coupling, Maxwell-Wagner effect due to the JT polaron and fast resistivity rise in LSMO layer is the main reason. This work emphasizes the crucial role of resistivity exchanges and of carrier accumulation at interfaces for the application of magnetoelectric heterojunction.

Poly(vinylidene fluoride-trifluoroethylene)/cobalt ferrite composite films with a self-biased magnetoelectric effect for flexible AC magnetic sensors

With the rapid development of artificial intelligence and wearable devices, flexible magnetic sensors have attracted much attention in recent years. In this work, large self-biased 0–3 type poly(vinylidene fluoride-trifluoroethylene)/cobalt ferrite (P(VDF-TrFE)/CoFe2O4) flexible magnetoelectric (ME) composite films are proposed for the development of AC magnetic sensors. P(VDF-TrFE)/CoFe2O4 composite films with CoFe2O4 nanoparticle mass contents from 5 to 30% are successfully fabricated through the solution casting method. The results show that the nanoparticles are homogeneously dispersed in the P(VDF-TrFE) matrix, and the composite films have both excellent ferroelectric and ferromagnetic properties. The P(VDF-TrFE)/CoFe2O4 composite films all exhibit a large ME effect. The ME coefficient reaches 47.1 mV·cm−1·Oe−1 for the film with a CoFe2O4 nanoparticle mass content of 20% at resonance frequency. Moreover, the composite films have a large self-biased ME effect with a maximum value of 20.4 mV·cm−1·Oe−1, which is mainly due to the high remnant magnetization of CoFe2O4 nanoparticles. To evaluate the composite films for application in magnetic sensors, the response of the ME output voltage to an AC magnetic field without a bias DC magnetic field was measured. The good linear correlation coefficient, sensitivity and repeatability indicate that the proposed 0–3 type P(VDF-TrFE)/CoFe2O4 composite film is a promising material for flexible AC magnetic sensors.

Strong modulation of magnetism in multiferroic CoFe2O4/0.7 Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 oxide composite films

Multiferroic magnetoelectric composite films have been becoming the research focus as the candidates for sensors, memories, spintronics and microwave devices. Compared to ferroelectric single crystal consisting of the heterostructure, the functional composite film realizes the magnetism control under only a few volts which brings the advantage of safety and low energy consumption in the memory devices. Here, the CoFe2O4/0.7PbMg1/3Nb2/3O3-0.3PbTiO3 oxide composite thin films were deposited on SrRuO3-buffered SrTiO3 substrate by pulsed laser deposition method. The structural, ferroelectric, magnetic and magnetoelectric properties have been studied respectively. The polarization reversibility of ferroelectric domain was investigated in the PMN-PT films by piezoresponse force microscopy. The coercive field of the CoFe2O4 film ranges from 900 Oe to 975 Oe under the applied direct current voltage. By performing the alternative current voltage modulated magneto-optical Kerr effect test, the dominating coupling mechanism in the composite films influenced by the CoFe2O4 film thickness was discussed. Our study indicates the potential application of electric field assisted magnetic data storage device.

Ferroelectric, ferromagnetic, and magnetoelectric properties of Bi3.15Nd0.85Ti2.9Zr0.1O12–CoFe2O4 composite films with large magnetoelectric coupling effect

The magnetoelectric composite films of Bi3.15Nd0.85Ti2.9Zr0.1O12 (BNTZO)–CoFe2O4 (CFO) were deposited on the substrates of Pt/Ti/SiO2/Si (111) by means of the sol–gel method. The results show that, in the composite films, there are tri-axial compressive stresses in the CFO films. Nevertheless, there are bi-axial tensile stresses and uniaxial compressive stress in the BNTZO films. The composite films possess compact microstructure and flat interface without forming intermediate layer. The composite films have good magnetoelectric properties besides both good ferroelectric and ferromagnetic properties. When Hdc is 738 Oe, the composite film of BNTZO-CFO possesses the maximum of αE, 114 mV cm−1 Oe−1, which is helpful for the application in multi-functional devices.

Room temperature multiferroicity and magnetodielectric coupling in 0–3 composite thin films

Magnetoelectric (ME) composite thin films are promising candidates for novel applications in future nanoelectronics, spintronics, memory, and other multifunctional devices as they exhibit much higher ME coupling and transition temperatures (Tc) than well-known single phase multiferroics discovered to date. Among the three types of multiferroic composite nanostructures, (2–2) layered and (1–3) vertically aligned composite nanostructures exhibit comparatively smaller ME coupling due to different shortcomings that restrict their use in many applications. Here, we study the morphological, piezoresponse force microscopic (PFM), ferroelectric, magnetic, and magnetodielectric properties of 0–3 [magnetic nanoparticles (0) homogeneously distributed in ferroelectric matrices (3)] multiferroic composite thin films. The Pb(Fe0.5Nb0.5)O3 (PFN)–Ni0.65Zn0.35Fe2O4 (NZFO) particulate composite films were synthesized by pulsed laser deposition. These particulate composite thin films are completely c-axis oriented with very low surface roughness. We observed magnetic and ferroelectric Tc above room temperature (RT) for all composite thin films. The PFN–NZFO 0–3 composites exhibit large polarization, high saturated magnetization with low coercive field, and low dielectric loss along with magnetodielectric coupling at RT. These nanocomposites might be utilized in next generation nano/microelectronics and spintronic devices.

Annealing heating rate dependence of microstructure and multiferroic properties in Bi4Ti2.9Fe0.1O12/CoFe2O4 layered magnetoelectric composite films prepared by chemical solution deposition method

Lead-free magnetoelectric composite films of CoFe2O4 (CFO) and Bi4Ti2.9Fe0.1O12 (BTF) were prepared on the LaNiO3-coated Si substrate by chemical solution deposition. Though the CFO layer randomly grows on the LaNiO3 layer, the oriented growth of the BTF layer can be regulated by rapid annealing treatment. The results indicated that the annealing heating rate significantly affects the c-axis orientation of the BTF layer, thereby resulting in obvious changes in microstructure, leakage behavior, dielectricity and ferroelectricity of the BTF/CFO films. The BTF/CFO film prepared at the heating rate of 40 °C/s presents the most compact structure, minimum leakage current, maximum dielectric constant and the highest residual polarization of 28.8 μC/cm2. Moreover, the excellent magnetoelectric coupling performance along with the highest magnetoelectric coupling voltage coefficient αE of 20.1 V/cm∙Oe can be achieved in these conditions.

Magnetoelectric response and tunneling magnetoresistance behavior of flexible P(VDF-H FP)/Cobalt ferrite nanofiber composite films

Fabrication of magnetoelectric (ME) polymer composite films by embedding ferromagnetic cobalt ferrite (CoFe2O4) nanofibers into electroactive poly(vinylidene fluoride–hexafluoropropylene) (P(VDF-HFP)) matrix is reported. Single-phase CoFe2O4 nanofibers made of cubic spinel nano crystallites are synthesized by using electro-spinning method, whereas the solution-casting technique is adapted to prepare flexible polymer composite films. The influence of CoFe2O4 nanofiber on structural, functional, magnetic, ferroelectric, and magnetoresistance properties of the composite films is investigated. The cross-coupling between ferroelectric and ferromagnetic orderings is ensured, by the variations of ferroelectric response at different magnetic fields. These magnetoelectric films are found to exhibit a negative tunneling magnetoresistance (TMR) effect with maximum TMR% of 28 for the film with 20 wt% of CoFe2O4 loading. The dielectric constant and electrical energy storage density of the films are increased with the addition of CoFe2O4 nanofiber. The ME films exhibiting TMR and high energy density can be the potential candidates for multifunctional device applications such as memory and spintronics devices, magnetic sensor, and bio-sensor.

Magnetoelectric composite films of La0.67Sr0.33MnO3 and Fe-substituted Bi4Ti3O12 fabricated by chemical solution deposition

Magnetoelectric composite layered films of La0.67Sr0.33MnO3 (LSMO) and Fe-substituted Bi4Ti3O12 (Bi4Ti3-xFexO12, BiTFx, x = 0.05, 0.10, 0.15 and 0.20) were fabricated on a LaNiO3-buffered silicon substrate by chemical solution deposition method. The LaNiO3 layer with c-axis orientation can not only induce the oriented growth of the overlaying LSMO and BiTFx layers, but also can act as an electrode material for electric measurements. The Fe-substituted content has a significant effect on the surface morphology of BiTFx phase, and leakage, dielectric and ferroelectric properties of the BiTFx/LSMO films. The BiTF0.10/LSMO composite film exhibits an improved leakage performance, the highest dielectric constant and the best ferroelectric properties. Furthermore, an interesting finding is that a weak ferromagnetism is present in the BiTF0.10 phase. The first-principle calculations suggest that the spin-resolved total density of states for BiTF0.10 are asymmetric, which can induce spin splitting and magnetic moments. The BiTF0.10/LSMO film also exhibits excellent magnetoelectric coupling performance, and its magnetoelectric coupling response is sensitive to AC magnetic frequency. The highest magnetoelectric coupling voltage coefficient can reach up to 47.5 V/cm·Oe without the presence of DC bias magnetic field.

Strong sub-resonance magnetoelectric coupling in PZT-NiFe[formula omitted]O[formula omitted]-PZT thin film composite

Magnetoelectric composite thin films of 2–2 type attract significant attention due to potentially high magnetoelectric (ME) coupling and ease of miniaturization. PbZr0.52Ti0.48O3 (PZT) and NiFe2O4 (NFO) have been among the materials of interest for the development of such composites, however, the obtained values of ME coefficients were sufficiently low so far. Also, these works report ME coupling in micrometer thick composite films. Here, we report strong magnetoelectric coupling (maximum longitudinal ME coefficient ≈ 1.2 V/cm⋅Oe at 100 kHz) obtained in nanograined PZT-NFO-PZT thin films of nanometer thickness fabricated on Si/SiO2/Ti/Pt substrates by sol–gel spin coating technique. This is a strong magnetoelectric coupling recorded in thin film composites involving ferrites at sub-resonant conditions and can be used in miniature transducers and sensors and for data processing devices.

Progresses of magnetoelectric composite films based on PbMg1/3Nb2/3O3-PbTiO3 single-crystal substrates

Owing to the rapid development of microelectronic technology,higher requirements are raised for miniaturization, intellectualization,sensitivity,reliability,low-power consumption and versatile functions of electromagnetic functional devices,but conventional block magnetic or electrical functional materials cannot meet those requirements mentioned above any longer.Layered magnetoelectric composites,by contrast,have ferroelectric,ferromagnetic and magnetoelectric properties,so they are possible to satisfy these demands above and be applied to the next-generation magnetoelectric functional devices.Layered magnetoelectric composites not only have rich physical phenomena and effects,but also possess broad application prospects in weak magnetic field detectors,multi-state memories,electric-write/magnetic-read memories,electrically tunable filters,phase shifters,antennas,etc,which have attracted extensive attention of material scientists and physicists.Among layered magnetoelectric composites,the functional thin film/ferroelectric single crystal heterostructures have aroused increasingly interest due to their simple preparation method,flexible structural design,effective electric field control and low power consumption.Currently,because of the excellent ferroelectric and piezoelectric properties of the (1 -x) PbMg1/3Nb2/3O3-xPbTiO3(PMN-PT) single crystal,the functional thin film/PMN-PT single crystal heterostructure has become one of the hot research topics in the multiferroic composite thin film material field.On this research topic,Chinese scientists have made their own significant contributions to the research of functional thin film/PMN-PT single crystal heterojunction.So far,researchers have built multiple types of thin film/PMN-PT heterostructures,such as manganese oxide/PMN-PT,ferrite/PMN-PT,ferromagnetic metal/PMN-PT,dilute magnetic semiconductor/PMN-PT,luminescent material/PMN-PT,two-dimensional material/PMN-PT,multi-layer film/PMN-PT,superconductive material/PMN-PT,etc.,and they have made great achievements in both theoretical and experimental studies.In this review,we summarize the research progress of magnetoelectric composite thin films based on PMN-PT single crystal substrates in the last decade.We first briefly describe the current status of articles related to functional film/PMN-PT heterostructures.Then we introduce the phase diagram and electric-field-induced strain properties of the PMN-PT single crystal around the morphotropic phase boundary.We also classify the heterostructures according to different categories of functional thin film materials and discuss the representative research findings of each category in the past few years.Our discussion focuses on the magnetoelectric properties of materials and the intrinsic physical mechanism.Finally,we also discuss the scientific problems to be solved and predict the possible application directions in the future.

Role of ferroelectric/ferromagnetic layers on the ferroelectric properties of magnetoelectric composite films derived by chemical solution deposition

Composite thin films with BiFeO3 (BFO), CoFeO4 (CFO) and/or BaTiO3 (BTO) layers as the components are fabricated via CSD method. XRD and Raman patterns show all the composite films can be indexed to perovskite and spinel structures. Except the interfaces between BTO and CFO layers, the other two-phase interfaces can be clearly observed. Interestingly, the BTO-CFO film has bigger polarization than BTO-BFO, especially the thickness of CFO layer is smaller than the BFO layer, implying the ferromagnetic layer has a significant impact on the ferroelectric properties of the composite films, which is too thin to be fully polarized. The variation of leakage currents show BTO-CFO film has the smallest value, corroborating the results of ferroelectric measurements. The leakage current is dominated by the space-charges-limited mechanisms according to the fitting results, and the oxygen vacancies in the BFO layers play an important role for the variations of ESCL and ETFL voltages.