O3 Heterostructures Research Articles

In-situ electric field-tailored exchange bias in the manganite/ferroelectric multiferroic heterostructures

The application of electric field-induced magnetic structure changes has significantly advanced nonvolatile data storage with ultralow energy consumption, as well as spintronics and quantum computing processes. In artificial perovskite oxide multiferroic structures composed of ferromagnetic and ferroelectric layers, the evolution of magnetic phases and ferroelectric domains often contribute to the magnetoelectric coupling. To fully understand the mechanisms behind electric field-induced changes in magnetic structures and enable the miniaturization of magnetoelectric devices, it is crucial to achieve local ferroelectric domain-triggered ferromagnetic evolution. In this study, we have fabricated La0.7Ca0.3MnO3/Pb(Zr0.52Ti0.48)O3 (LCMO/PZT) heterostructures, where the magnetic phase separation of LCMO and the ferroelectric domain of PZT can be modulated by substrates and piezoelectric force microscopy, respectively. Our experiments demonstrate that by switching the polarization states of PZT, we can observe electric field control of the magnetic exchange bias effect through changes in the phase separation of the LCMO layer. These results contribute to the development of magnetoelectric devices with enhanced properties and offer valuable insights for future design strategies.

Design and Construction of Carbon-Coated Fe3 O4 /Cr2 O3 Heterostructures Nanoparticles as High-Performance Anodes for Lithium Storage.

Transition metal oxides, highly motivated anodes for lithium-ion batteries due to high theoretical capacity, typically afflict by inferior conductivity and significant volume variation. Architecting heterogeneous structures with distinctive interfacial features can effectively regulate the electronic structure to favor electrochemical properties. Herein, an engineered carbon-coated nanosized Fe3 O4 /Cr2 O3 heterostructure with multiple interfaces is synthesized by a facile sol-gel method and subsequent heat treatment. Such ingenious components and structural design deliver rapid Li+ migration and facilitate charge transfer at the heterogeneous interface. Simultaneously, the strong coupling synergistic interactions between Fe3 O4 , Cr2 O3 , and carbon layers establish multiple interface structures and built-in electric fields, which accelerate ion/electron transport and effectively eliminate volume expansion. As a result, the multi-interface heterostructure, as a lithium-ion battery anode, exhibits superior cycling stability maintaining a reversible capacity of 651.2 mAh g-1 for 600 cycles at 2 C. The density functionaltheorycalculations not only unravel the electronic structure of the modulation but also illustrate favorable lithium-ion adsorption kinetics. This multi-interface heterostructure strategy offers a pathway for the development of advanced alkali metal-ion batteries.

Nonmonotonic anomalous Hall effect and anisotropic magnetoresistance in SrRuO3/PbZr0.52Ti0.48O3 heterostructures

We fabricate SrRuO3/PbZr0.52Ti0.48O3 heterostructures each with an in-plane tensile-strained SrRuO3 layer and investigate the effect of an applied electric field on anomalous Hall effect. The four-fold symmetry of anisotropic magnetoresistance and the nonmonotonic variation of anomalous Hall resistivity are observed. By applying positive electric field or negative electric field, the intersecting hump-like feature is suppressed or enhanced, respectively. The sign and magnitude of the anomalous Hall conductivity can be effectively controlled with an electric field under a high magnetic field. The electric-field-modulated anomalous Hall effect is associated with the magnetization rotation in SrRuO3. The experimental results are helpful in modulating the magnetization rotation in spintronic devices based on SrRuO3 heterostructures.

Self-powered ultraviolet/visible photodetector based on CuBi2O4/PbZr0.52Ti0.48O3 heterostructure

Ferroelectric materials with significant remnant electric polarization have recently gained research focus for the fabrication of self-power photodetectors due to their photovoltaic effect. However, the photodetectors based on ferroelectric materials display poor performance owing to their weak photovoltaic effect of the ferroelectric depolarization field (Ed) on photo-generated charge carrier separation. In this work, we fabricate self-powered photodetectors based on CuBi2O4/PZT heterostructure. The heterojunction reveals a photoresponsivity of 0.24 mA/W and a detectivity of 2.40 × 1010 Jones under 0 V bias with a maximum 7.51 μW/cm2 illumination intensity at 425 nm, which is substantially improved compared to PZT-only device. The observed rise and fall time of the composite CuBi2O4/PZT thin film is around 24 and 46 ms, respectively, which is faster than that of PZT photodetector (67 and 106 ms). Moreover, the photocurrent CuBi2O4/PZT of device is observed to be 12.7 × 10−10 A in the downpoling state and 6.28 × 10−10 A in upward poling state, revealing that the direction of polarization field can modulate the photocurrent. This work provides a promising strategy for fabricating ferroelectric heterojunction photodetectors with enhanced performance.

Interfacial Engineering of Ni/V2 O3 Heterostructure Catalyst for Boosting Hydrogen Oxidation Reaction in Alkaline Electrolytes.

Alkaline fuel cells can permit the adoption of platinum group metal-free (PGM-free) catalysts and cheap bipolar plates, thus further lowering the cost. With the exploration of PGM-free hydrogen oxidation reaction (HOR) catalysts, nickel-based compounds have been considered as the most promising HOR catalysts in alkali. Here we report an interfacial engineering through the formation of nickel-vanadium oxide (Ni/V2 O3 ) heterostructures to activate Ni for efficient HOR catalysis in alkali. The strong electron transfer from Ni to V2 O3 could modulate the electronic structure of Ni sites. The optimal Ni/V2 O3 catalyst exhibits a high intrinsic activity of 0.038 mA cm-2 and outstanding stability. Experimental and theoretical studies reveal that Ni/V2 O3 interface as the active sites can enable to optimize the hydrogen and hydroxyl bindings, as well as protect metallic Ni from extensive oxidation, thus achieving the notable activity and durability.

Continuous modulation of charge-spin conversion by electric field in Pt/Co2FeSi/Pb(Mg1/3Nb2/3)O3-Pb0.7Ti0.3O3 heterostructures

The half-metallic Heusler alloy Co2FeSi is an ideal material in spintronic devices due to its higher spin polarization, higher Curie temperature and lower damping parameters. In this work, the dynamic magnetism of Co2FeSi is modulated by electric field and it is demonstrated that the charge-spin conversion efficiency ξ is continuous and controllable by the electric field. We further find an extremely high ξ in ferromagnetic/ferroelectric (FM/FE) heterostructures, which could be ascribed to interfacial effect in FM/FE interface. Moreover, we investigate that the charge-spin conversion efficiency varies with the electric field in a butterfly-like behavior, which accords with the S–E curve of Pb(Mg1/3Nb2/3)O3-Pb0.7Ti0.3O3(PMN-PT) and could be attributed to strain effect. The modulation of charge-spin conversion efficiency in FM/FE heterostructures via electric field presents a profound potential for next-generation spintronic devices and applications of current-induced magnetization switching.

Tailoring large magnetoresistance in Dirac semimetal SrIrO3 films

Perovskite SrIrO3 is a special Dirac material with fascinating effects due to its strong electron correlation and spin–orbit coupling. In this work, a large magnetoresistance (MR) was observed not only in epitaxial SrIrO3 films but also in a SrIrO3/PbZr0.2Ti0.8O3 epitaxial heterostructure with a magnetic field applied perpendicular to the external electric field. The magnetoresistance of SrIrO3 (10 nm) and SrIrO3/PbZr0.2Ti0.8O3 (10 nm/30 nm) reach values as large as 40% and 110% at 9 T and 5 K, respectively. We believe that the unusual magnetoresistance is from the Dirac/Weyl state. Especially, the SrIrO3/PbZr0.2Ti0.8O3 bilayer shows negative magnetoresistance with strong oscillations close to the angle positions, where the magnetic field is parallel to the electric field at 1.8 K, which arises from the chiral anomaly. Based on first-principle calculations and study, the polarization field of PbZr0.2Ti0.8O3 can modulate the band structure of SrIrO3, which can modify the MR of SrIrO3. The SrIrO3/PbZr0.2Ti0.8O3 heterostructure accommodating both the ferroelectric property and the Dirac/Weyl state may open the avenue to manipulate the Dirac/Weyl properties via the electric polarization field.

Electrically tunable inverse spin Hall effect in SrIrO3/Pb(Mg1/3Nb2/3)0.7 Ti0.3O3 heterostructures through interface strain coupling

Oxide spin detector materials are highly desired for emergent all-oxide spintronics. In this work, Permalloy/SrIrO3/Pb(Mg1/3Nb2/3)0.7 Ti0.3O3 (Py/SIO/PMNPT) heterostructures were prepared by pulsed laser deposition of SIO thin films epitaxially on (001)-oriented single crystalline PMNPT substrates, followed by sputter deposition of Py films upon SIO through a shadow mask. The paramagnetic SIO layer, with a large spin–orbit coupling, serves as a detector to check the spin current pumped from the adjacent ferromagnetic Py layer through the inverse spin Hall effect (ISHE). It is observed that the spin pumping amplitude can be reversibly tuned by about 50% through applying a 10 kV/cm electric field on the piezoelectric PMNPT substrate. The ISHE voltage shows a butterfly hysteresis resembling the strain-field curve of PMNPT, indicating the relevance of strain coupling at the SIO/PMNPT interface. In situ x-ray diffraction reveals that both in-plane and out-of-plane lattice parameters of SIO vary with the field applied on PMNPT. These results highlight that SIO is a promising candidate material for spin detection, and the efficiency of spin to charge conversion in SIO can be tuned electrically in SIO/PMNPT heterostructures.

Heterostructure Engineering of Core-Shelled Sb@Sb2 O3 Encapsulated in 3D N-Doped Carbon Hollow-Spheres for Superior Sodium/Potassium Storage.

In this work, the core-shelled Sb@Sb2 O3 heterostructure encapsulated in 3D N-doped carbon hollow-spheres is fabricated by spray-drying combined with heat treatment. The novel core-shelled heterostructures of Sb@Sb2 O3 possess a mass of heterointerfaces, which formed spontaneously at the core-shell contact via annealing oxidation and can promote the rapid Na+ /K+ transfer. The density functional theory calculations revealed the mechanism and significance of Na/K-storage for the core-shelled Sb@Sb2 O3 heterostructure, which validated that the coupling between the high-conductivity of Sb and the stability of Sb2 O3 can relieve the shortcomings of the individual building blocks, thereby enhancing the Na/K-storage capacity. Furthermore, the core-shell structure embedded in the 3D carbon framework with robust structure can further increase the electrode mechanical strength and thus buffer the severe volume changes upon cycling. As a result, such composite architecture exhibited a high specific capacity of ≈573 mA h g-1 for sodium-ion battery (SIB) anode and ≈474 mA h g-1 for potassium-ion battery (PIB) anode at 100 mA g-1 , and superior rate performance (302 mA h g-1 at 30 A g-1 for SIB anode, while 239 mA h g-1 at 5 A g-1 for PIB anode).

Promoted Photocharge Separation in 2D Lateral Epitaxial Heterostructure for Visible-Light-Driven CO2 Photoreduction.

Photocarrier recombination remains a big barrier for the improvement of solar energy conversion efficiency. For 2D materials, construction of heterostructures represents an efficient strategy to promote photoexcited carrier separation via an internal electric field at the heterointerface. However, due to the difficulty in seeking two components with suitable crystal lattice mismatch, most of the current 2D heterostructures are vertical heterostructures and the exploration of 2D lateral heterostructures is scarce and limited. Here, lateral epitaxial heterostructures of BiOCl @ Bi2 O3 at the atomic level are fabricated via sonicating-assisted etching of Cl in BiOCl. This unique lateral heterostructure expedites photoexcited charge separation and transportation through the internal electric field induced by chemical bonding at the lateral interface. As a result, the lateral BiOCl @ Bi2 O3 heterostructure demonstrates superior CO2 photoreduction properties with a CO yield rate of about 30µmol g-1 h-1 under visible light illumination. The strategy to fabricate lateral epitaxial heterostructures in this work is expected to provide inspiration for preparing other 2D lateral heterostructures used in optoelectronic devices, energy conversion, and storage fields.

Demonstration of a pseudo-magnetization based simultaneous write and read operation in a Co60Fe20B20/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructure

Taking advantage of the magnetoelectric and its inverse effect, this article demonstrates strain-mediated magnetoelectric write and read operations simultaneously in Co60Fe20B20/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructures based on a pseudo-magnetization µ ≡ mx2 − my2. By applying an external DC-voltage across a (011)-cut PMN-PT substrate, the ferroelectric polarization is re-oriented, which results in an anisotropic in-plane strain that transfers to the CoFeB thin film and changes its magnetic anisotropy Hk. The change in Hk in-turn results in a 90° rotation of the magnetic easy axis for sufficiently high voltages. Simultaneously, the inverse effect is employed to read changes of the magnetic properties. The change of magnetization in ferromagnetic (FM) layer induces an elastic stress in the piezoelectric (PE) layer, which generates a PE potential that can be used to readout the magnetic state of the FM layer. The experimental results are in excellent qualitative agreement with an equivalent circuit model that considers how magnetic properties are electrically controlled in such a PE/FM heterostructure and how a back-voltage is generated due to changing magnetic properties in a self-consistent model. We demonstrated that a change of easy axis of magnetization due to an applied voltage can be directly used for information processing, which is essential for future ME based devices.

Differentiation of non-volatile strain and ferroelectric field effects in (011)- and (001)-La0.67Sr0.33MnO3/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructures

La0.67Sr0.33MnO3 (LSMO) thin films were fabricated on (011)- and (001)-Pb(Mg1/3Nb2/3)1 − xTixO3 (PMN-PT) substrates to investigate the mechanism of electric field regulation. Both (011)- and (001)-LSMO/PMN-PT heterostructures exhibit electric-field-dependent resistance curves with an asymmetric butterfly shape under a bipolar electric field (±10 kV/cm). Confirmed through a mathematical method, the “butterfly” and “asymmetric” characteristics indicate the volatile strain and non-volatile ferroelectric field effects, respectively. However, by applying a unipolar electric field, the electric-field-dependent resistance curves of the (011)-LSMO/PMN-PT heterostructures present a larger loop shape than those in the (001)-LSMO/PMN-PT heterostructure, which is related to the non-volatile strain effect. The volatile strain, non-volatile strain, and ferroelectric field effects on the resistance of the LSMO films are associated with the enhanced or weakened double exchange coupling.

Voltage-controlled three-state magnetic memory based on anisotropic magnetoresistance in a multiferroic heterostructure

An energy efficient technique has shown to produce a three-state magnetic memory cell in a [011]-poled Ni80Co20/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) heterostructure. Via the magnetic field deposition, a 45° magnetic easy axis of the NiCo film was induced in the film plane. By using a strong converse magnetoelectric coupling between the NiCo film and the PMN-PT, the magnetic moments of NiCo can be modulated to [001] and [1-10] directions of PMN-PT by selecting an appropriate electric field (E-field). Consequently, large, medium, and small anisotropic magnetoresistance (AMR) values are obtained by fixing a measuring current along the [001] direction. The required E-field significantly reduces due to the initial direction of NiCo along the 45° direction. The tunability of the AMR ratio is as large as ∼87%. These results indicate that an energy efficient approach to generate magnetic storage by using only a small E-field rather than a magnetic field with a high energy consumption was realized. This work shows great potential for the development of ultra-low power and high-density magnetoresistive memory devices.

Electric-field-mediated magnetic properties of all-oxide CoFe2O4/La0.67Sr0.33MnO3/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructures.

Electric-field-mediated magnetic properties were investigated in CoFe2O4/La0.67Sr0.33MnO3/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (CFO/LSMO/PMN-PT) heterostructures. The butterfly-like behavior of the magnetization under different electric fields indicates that the strain effect plays a critical role in the electric-field-mediated magnetic properties, leading to an increase in magnetization along the [100] direction but a decrease along the [01-1] direction in the CFO/LSMO/PMN-PT heterostructures. More interestingly, due to the large magnetostriction of the CFO layer, the coercivity of the CFO/LSMO/PMN-PT heterostructures decreases ∼50% along the [01-1] direction under the electric fields. The large modulation of the coercivity makes it possible to achieve electric-field-controlled magnetoresistance in the metal/CFO/LSMO/PMN-PT spin filter magnetic tunneling junctions.

Strain effect on magnetoelectric coupling of epitaxial NFO/PZT heterostructure

NiFe2O4/Pb(Zr0·52Ti0.48)O3 (NFO/PZT) heterostructures were epitaxially grown on (001) SrTiO3 substrates via pulsed laser deposition. The PZT layers with various thicknesses were deposited between the substrate and the NFO layer, which acted as a piezoelectric layer as well as effectively reduced the mechanical constraints imposed by the substrate to the magnetic layer. The misfit strain in both PZT and NFO layers decreases with the increase of the PZT thickness. The ferroelectric, magnetic and magnetoelectric properties of the heterostructures are highly dependent on the PZT thickness. A large ME coefficient of 240 mV/cm•Oe with a PZT thickness of 170 nm was achieved. The magnetoelectric coupling effects were further confirmed by the magneto-capacitance measurements and a magnetodielectric response of ∼10% was revealed in the heterostructure with a PZT thickness of 170 nm. This work will be of significance for tuning magnetoelectric response via thickness ratio between ferroelectric and ferromagnetic layers.

Thickness-dependent polarization-induced intrinsic magnetoelectric effects in La0.67Sr0.33MnO3/PbZr0.52Ti0.48O3 heterostructures

The self-polarization of PbZr0.52Ti0.48O3 thin film is switched by changing film thickness through the competition between the strain relaxation-induced flexoelectric fields and the interfacial effects. Without an applied electric field, this reversal of self-polarization is exploited to control the magnetic properties of La0.67Sr0.33MnO3 by the competition/cooperation between the charge-mediated and the strain-mediated effects. Scanning transmission electron microscopy, polarized near edge x-ray absorption spectroscopy, and half-integer diffraction measurements are employed to decode this intrinsic magnetoelectric effects in La0.67Sr0.33MnO3/PbZr0.52Ti0.48O3 heterostructures. With PbZr0.52Ti0.48O3 films < 48 nm, the self-polarization-driven carrier density modulation around La0.67Sr0.33MnO3/PbZr0.52Ti0.48O3 interface and the strain-mediated Mn 3d orbital occupancy work together to enhance magnetism of 14 unit cells La0.67Sr0.33MnO3 film; with PbZr0.52Ti0.48O3 layers > 48 nm, the strain-induced the change of bond length/angle of MnO6 accompanied with a modified spin configuration are responsible for the decrease in Curie temperature and magnetization of 14 unit cells La0.67Sr0.33MnO3 film.

Magnetoelectric Effect in Co/PbZr0.45Ti0.55O3 Heterostructures with a Shaped Interface

Magnetoelectric Effect in Co/PbZr0.45Ti0.55O3 Heterostructures with a Shaped Interface

Structural and chemical investigation of interface related magnetoelectric effect in Ni/BiFe0.95Mn0.05O3 heterostructures

The magnetoelectric coupling mechanism in Ni/BiFe0.95Mn0.05O3 heterostructures is investigated through a detailed microstructural study of the BiFe0.95Mn0.05O3 film and a chemical analysis of the Ni/BiFe0.95Mn0.05O3 interface. The four structural variants expected in BiFe0.95Mn0.05O3 are detected by high resolution X-ray diffraction reciprocal space mapping method. The ferroelectric domain structure is imaged with transmission electron microscopy. Oxidized Ni is evidenced at the Ni/BiFe0.95Mn0.05O3 interface by electron energy loss spectroscopy and X-ray photoemission spectroscopy, although the degree of Ni oxidation is independent of the magnetoelectric state of the heterostructure.

Ferroelectric and dielectric behaviors of sol-gel derived perovskite PMN-PT/PZT heterostructures via compositional development: An interface-dependent study

Phase-pure perovskite 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3/Pb(Zr0.52Ti0.48)O3 (PMN-PT/PZT) heterostructures were prepared via compositional development using a sol-gel route. Interface-dependent microstructure, insulating, ferroelectric and dielectric performance were investigated. Relatively enhanced ferroelectricity (Pr = 21.81 μC/cm2, Ec = 61.88 kV/cm) and dielectricity (εr = 1959, tanδ = 0.0152) were obtained for the heterostructure with the maximum number of interfaces (7 interfaces, namely F-7 type). Presumably, this behavior is due to the reduced leakage current density (10−9–10−8 A/cm2 at ±400 kV/cm), which arises from columnar grain growth mode with more depletion layers generated between different compositions acting as a potential barrier for the movement of free carriers. A simplified equivalent circuit is used to provide a comprehensive explanation of the enhanced performance mechanism. These results highlight inherent issues in designing structures with specific interfaces and provide a new approach for designing high-performance PMN-PT-based thin film.

Local rotations due to mixed-type misfit dislocation at α-Fe2 O3 /α-Al2 O3 heterostructure interface.

The misfit dislocations at α-Fe2 O3 /α-Al2 O3 heterostructure interfaces were investigated by high-resolution transmission electron microscopy (HRTEM), geometric phase analysis (GPA) and dislocation density tensor analysis. When imaged along the [112¯0] direction, the misfit dislocation core is a mixed-type, which can be characterised by one extra (11¯02) plane and one extra (1¯104) plane of α-Al2 O3 . Dislocation density tensor analysis gave a very high accuracy in determining the corresponding Burgers vectors of two extra half-planes. By comparing the measured Burgers vectors with theoretical ones, we are able to determine local rotations in the dislocation core region: the (11¯02) plane is rotated clockwise 6.25° and the (1¯104) plane is rotated anticlockwise 4.81°. Such a local rotation is favourable from the viewpoint of both energy and function to relax lattice misfit.