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The heterostructures based on multiferroic BiFeO3 (BFO) have received much attention for the great potential in magnetoelectric coupling and spintronic applications. Therefore, the BFO films combined with rhombohedral (R) phase and tetragonal (T) phase can bring in various functionalities. Here, we demonstrate that the Ta/Pt/Co/Pt multilayers grown on R-, T-, and mixed-phase BFO exhibit perpendicular magnetic anisotropy. We find that the magnetic switching behavior of the multilayer is sensitive to the phase of the BFO layer. The Ta/Pt/Co/Pt layers grown on top of the pure R- or T-phase BFO show one-step anomalous Hall effect (AHE) switching. However, the layers grown on the mixed-phase BFO show steplike AHE switching. We attribute that the steplike switching behavior originates from the two different interfacial situations between mixed-phase BFO and above layers. Our results bring a potential avenue for realizing spintronic devices based on mixed-phased BFO.

Large data storage at reduced dimension is of a great deal of interest in spintronic devices in which magnetic oxide films lead for realizing the modulation of perpendicular magnetic anisotropy (PMA). Herein, we report the modulation of PMA in oxide heterostructures composed of one manganite layer sandwiched between two cobaltite layers, i.e., LaCoO3− δ/La0.7Sr0.3MnO3/LaCoO3− δ via oxygen vacancies. The PMA is originated by the orbital reconstruction and ferromagnetic exchange interaction at the interface between the CoO6 and MnO6 octahedra layers. The modulation ratio up to a significant value ∼200% of PMA can be realized through the phase transition of LaCoO3− δ layers between perovskite and brownmillerite via deprivation or replenishment of oxygen sites. The antiferromagnetic superexchange interaction at the interface between the oxygen-deficient CoO4 tetrahedra layer and the adjacent MnO6 octahedral layer with lattice distortion may suppress the magnetization and PMA. This work ensures promising outcomes in situ modulation of PMA in oxide films such as ferroelectric polarization or ionic liquid gating via the transport of oxygen vacancies.

Exchange bias lies in the core of cutting-edge technologies, for instance, high-density data storage, spin valves, and high-frequency magnetic devices. As the devices with flexibility have become vital in the forefront of technology, the maintenance of exchange bias under high flexion is highly desired. This paper reports the strong exchange bias in flexible freestanding La0.7Sr0.3MnO3/BiFeO3 membranes with decent mechanical durability. The La0.7Sr0.3MnO3 layer is biased strongly by the BiFeO3 layer even in the freestanding state. At the same time, the strain is demonstrated to affect the strength of the exchange bias of the La0.7Sr0.3MnO3/BiFeO3 bilayer. Furthermore, the saturation magnetization and exchange bias field of the freestanding La0.7Sr0.3MnO3/BiFeO3 membranes are preserved well after 1000 bending cycles. Our work on freestanding membranes paves the way for manufacturing advanced flexible spintronic devices.

The evidence for a spin-lattice coupling in a tetragonal-like BiFeO3 (BFO) film is derived from thermal expansion measurements. Taking the advantage of La doping, the Neel temperature (TN) of the BFO film can be further adjusted over a broad range of temperatures. The lattice parameters exhibit anomalies near the Neel temperatures. The Bi0.8La0.2FeO3 film has a spin order-to-disorder transition at the TN without a structural phase transition, suggesting that a spin-lattice coupling drives the thermal expansion anomalies. The spin-lattice coupling can be enhanced by the coexistence of phases in the thicker BFO films. The density functional theory calculations show a smaller lattice constant of the c axis in the spin-order state than that in the spin-disorder state for the same tetragonal-like phase, which supports that the thermal expansion anomalies are a consequence of the spin-lattice coupling. Our findings may have application prospects for functional materials with controllable thermal expansions.

Magnetism control has a variety of applications in magnetic storage and spintronic devices. Instead of the control of direct magnetoelectric coupling via strain, voltage, and Dzyaloshinskii-Moriya interaction, the polarization-dependent coupling in multiferroic materials such as BiFeO3 is employed for the electric-field control of magnetizations in this work. A perpendicular magnetic anisotropy (PMA) has been realized in a BiFeO3/Al2O3/Pt/Co/Pt multiferroic structure at room temperature. Interestingly, a distinct change of coercivity field (∼400%) has been observed in the structure with opposite polarization directions, which can be attributed to the different oxidation degree at the Pt/Co interface. This spontaneous polarization-controlled switching not only provides us a platform to study the interfacial effect in multiferroic heterostructures but also paves the way to manipulate PMA or even spin orbit torque through oxygen vacancies.

The effect of oxide/oxide interface for controlling the migration process of oxygen vacancies (or oxygen ions) on resistive switching behaviors has been investigated by fabricating the ZrO2/ZnO oxide heterostructures. Completely different resistive switching behaviors are observed in the heterostructures with a set process under a different bias polarity. It is demonstrated that the change of the oxide/oxide interface barrier height determining the migration of oxygen vacancies (or oxygen ions) leads to the current direction-dependent resistive switching. Furthermore, the ZnO/ZrO2 heterostructure with the homogeneous resistive switching behavior could be potentially applied as a controllable and stable multistate memory by controlling reset-stop voltages. Our method opens up an opportunity to explore the resistive switching mechanism and develop resistance switching devices with specific functions through engineering oxide/oxide interfaces in oxide heterostructures.