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Highlights: The (001)-oriented ferromagnetic La0.67Sr0.33MnO3 films are stuck onto the (011)-oriented ferroelectric single-crystal 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 substrate with 0° and 45° twist angle. By applying a 7.2 kV cm−1 electric field, the coexistence of uniaxial and fourfold in-plane magnetic anisotropy is observed in 45° Sample, while a typical uniaxial anisotropy is found in 0° Sample. Manipulating strain mode and degree that can be applied to epitaxial complex oxide thin films have been a cornerstone of strain engineering. In recent years, lift-off and transfer technology of the epitaxial oxide thin films have been developed that enabled the integration of heterostructures without the limitation of material types and crystal orientations. Moreover, twisted integration would provide a more interesting strategy in artificial magnetoelectric heterostructures. A specific twist angle between the ferroelectric and ferromagnetic oxide layers corresponds to the distinct strain regulation modes in the magnetoelectric coupling process, which could provide some insight in to the physical phenomena. In this work, the La0.67Sr0.33MnO3 (001)/0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (011) (LSMO/PMN-PT) heterostructures with 45º and 0º twist angles were assembled via water-etching and transfer process. The transferred LSMO films exhibit a fourfold magnetic anisotropy with easy axis along LSMO < 110 >. A coexistence of uniaxial and fourfold magnetic anisotropy with LSMO [110] easy axis is observed for the 45° Sample by applying a 7.2 kV cm−1 electrical field, significantly different from a uniaxial anisotropy with LSMO [100] easy axis for the 0° Sample. The fitting of the ferromagnetic resonance field reveals that the strain coupling generated by the 45° twist angle causes different lattice distortion of LSMO, thereby enhancing both the fourfold and uniaxial anisotropy. This work confirms the twisting degrees of freedom for magnetoelectric coupling and opens opportunities for fabricating artificial magnetoelectric heterostructures. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Epitaxial BiEuFeO (BEFO) thin films are deposited on Nb-doped SrTiO (NSTO) substrates by pulsed laser deposition to fabricate the Pt/BEFO/NSTO (001) heterostructures. These heterostructures possess bipolar resistive switching, where the resistances versus writing voltage exhibits a distinct hysteresis loop and a memristive behavior with good retention and anti-fatigue characteristics. The local resistive switching is confirmed by the conductive atomic force microscopy (C-AFM), suggesting the possibility to scale down the memory cell size. The observed memristive behavior could be attributed to the ferroelectric polarization effect, which modulates the height of potential barrier and width of depletion region at the BEFO/NSTO interface. The continuously tunable resistive switching behavior could be useful to achieve non-volatile, high-density, multilevel random access memory with low energy consumption. [ABSTRACT FROM AUTHOR]

We report the epitaxial growth of multiferroic BiFeO3 (BFO) film on Si(001) substrate by pulsed laser deposition using CeO2/yttria-stabilized zirconia (YSZ) as buffer layers. The epitaxial relationships of the films were BFO(001)/CeO2(001)/YSZ(001)/Si(001) for out-of-plane and [110]BFO|[100]CeO2|[100]YSZ|[100]Si for in-plane, respectively. Capacitance-voltage characteristics of a Pt/BFO/CeO2/YSZ/p-Si capacitor exhibited clockwise hysteresis loops with a large memory window of 2.5 V at sweeping voltages of ±16 V. Both the high and low capacitance values showed no obvious degradation after 104 s. The improved retention property was attributed to the use of high-k CeO2/YSZ insulating layers that effectively eliminated the charge trapping in the heterostructure. [ABSTRACT FROM AUTHOR]

Perpendicular exchange bias (EB), which combines perpendicular magnetic anisotropy and ferromagnetic (FM)–anti‐ferromagnetic (AFM) exchange coupling, is extremely important in high‐density AFM spintronics. However, the effective modulation of EB remains challenging, since the alternant spins at the AFM/FM interface are strongly pinned by the AFM layer. Voltage tuning of EB through magnetoelectric coupling provides a potential way to achieve rapid magnetization switching in an energy‐efficient manner. Nevertheless, the interfacial strain mediation of perpendicular EB induced by E‐field remains unexplored. In this work, perpendicular EB nanostructure by room‐temperature fabrication process is obtained, and the voltage tunable perpendicular EB in Pt/IrMn/(Co/Pt)2/Ta/(011) Pb(Mg1/3Nb2/3)O3‐PbTiO3 multiferroic heterostructure is demonstrated. To enhance the voltage control effect on perpendicular EB, both strain‐mediated magnetoelectric coupling and ionic liquid gating method are further investigated in the thinned EB system with the structure of Pt/IrMn/Co/Pt/Ta. As a result, the voltage induced lattice distortion effectively transmits to the AFM/FM interface, while the charge accumulation and ion migrations in gating method generate a relatively large hysteresis loop offset that has not been observed before at room temperature. The voltage manipulation of perpendicular EB at room temperature provides new possibilities toward novel AFM devices and memories with great energy‐efficiency and ultrahigh density. [ABSTRACT FROM AUTHOR]

Magnetization dynamics induced by spin–orbit torques in a heavy‐metal/ferromagnet can potentially be used to design low‐power spintronics and logic devices. Recent computations have suggested that a strain‐mediated spin–orbit torque (SOT) switching in magnetoelectric (ME) heterostructures is fast, energy‐efficient, and permits a deterministic 180° magnetization switching. However, its experimental realization has remained elusive. Here, the coexistence of the strain‐mediated ME coupling and the SOT in a CoFeB/Pt/ferroelectric hybrid structure is shown experimentally. The voltage‐induced strain only slightly modifies the efficiency of SOT generation, but it gives rise to an effective magnetic anisotropy and rotates the magnetic easy axis which eliminates the incubation delay in current‐induced magnetization switching. The phase field simulations show that the electric‐field‐induced effective magnetic anisotropy field can reduce the switching time approximately by a factor of three for SOT in‐plane magnetization switching. It is anticipated that such strain‐mediated ME‐SOT hybrid structures may enable field‐free, ultrafast magnetization switching. A strain‐mediated magnetoelectric‐spin‐torque hybrid structure, which combines the advantages of spin orbit torque‐ and magnetoelectric‐ driven magnetization dynamics together, is developed. Via a magentoelectric effect, voltage‐controlled magnetic anisotropy is demonstrated in spin–orbit torque devices, which can lead to a reduction of the magnetization switching time by a factor of three. The findings provide a new platform for fast and low‐power spintronics. [ABSTRACT FROM AUTHOR]

A TiO2 thin film was deposited on a Nb : SrTiO3 substrate by pulsed laser deposition to form an Ag/TiO2/Nb : SrTiO3/In device. The bipolar resistive switching (RS) effect of this device was investigated. The current–voltage characteristics exhibited pronounced and stable bipolar RS features. The device could be switched to a low resistance state (LRS) at forward voltage and returned to a high resistance state (HRS) at reverse voltage, and the RS ratio RHRS/RLRS reached up to 2 × 103 at a read voltage of −0.5 V. Moreover, the RS ratio could be adjusted by changing the maximum value of the forward or reverse voltage, which shows promise for multilevel memories. These results are discussed by considering carrier injection-trapped/detrapped process of the heterostructure and show high potential for nonvolatile memory applications. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports the bipolar resistive switching effect in a SrTiO3/NiO stacked heterostructure which was epitaxially deposited on an Nb doped SrTiO3 substrate by pulsed laser deposition. This heterostructure shows high resistive switching ratio of over 104 at the read voltage of −0.5V and an expected retention ability of ten years, which is better than that of NiO-based device. Moreover, the resistive switching ratio can be adjusted by changing the maximum applied voltage or compliance current, which shows promising for multilevel nonvolatile memories application. Meanwhile, these results have been discussed by carrier injection-trapped/detrapped process. [Copyright &y& Elsevier]

Multilayer Pt/BaTiO 3 /BiFeO 3 /TiO 2 heterostructure was fabricated on FTO substrates by sol-gel technique. This heterostructure shows strong light absorption, sensitive optical switching response, and excellent photovoltaic properties, which are effectively modulated by the ferroelectric polarization. The short circuit current density and open circuit voltage of the multilayer heterostructure are significantly enhanced compared with that of the single layer BiFeO 3 thin film under the initial and positive polarization states. Analysis on the schematic energy band diagrams suggests that the excellent photovoltaic properties can be attributed to the interface Schottky barrier regulated by ferroelectric polarization, in which the TiO 2 layer acts as the electron collection layer, and the ferroelectric BaTiO 3 layer acts as a hole collection layer and also an auxiliary photovoltaic absorption layer to enhance optical absorption properties, thus improve the light absorption efficiency and the separation of electron-hole pairs. These results provide a promising method to optimize the performance of ferroelectric photovoltaic devices by using multilayer heterostructure. [ABSTRACT FROM AUTHOR]

Amorphous FeBSiC thin films were deposited on PMN-PT (Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 )(001) single crystal substrate by DC magnetron sputtering. The effects of piezoelectric-poling-induced strain on the magnetic properties of the FeBSiC/PMN-PT heterostructures were investigated. Studies indicated that the non-linear strains in PMN-PT were induced by poling at different electric fields, with tensile strain for out-of-plane direction and compressive strain for in-plane direction, respectively. Moreover, the in-plane compressive strain increased the saturation magnetization of the FeBSiC thin film, while the out-of-plane tensile strain decreased it. These results could be attributed to the 109° ferroelastic domain switching at applied electric field, which induced large variation in magnetic anisotropy due to magnetoelectric coupling in the FeBSiC/PMN-PT heterostructures. This study demonstrates the non-volatile tuning of magnetism by non-linear strains of lattice induced by the piezoelectric-poling, which shows promising applications for energy efficient magnetoelectric devices. [ABSTRACT FROM AUTHOR]