Doped‐HfO2 thin films with ferroelectricity have attracted great attention due to their potential application in semiconductor industry as negative capacitance and resistance switching memory. Despite Hf0.5Zr0.5O2 (HZO) thin films having the most robust ferroelectric properties among all doped‐HfO2 thin films, the realization of single orthorhombic phase HZO thin films is not achieved, while the direct evidence between the structural–properties relationship of orthorhombic phase HZO and ferroelectricity is not confirmed. In this work, the growth of single orthorhombic phase HZO thin films with decent ferroelectricity and resistive switching behavior is reported. With the aid of advanced structural characterization techniques, the HZO thin film is confirmed to be in the single orthorhombic phase. Next, using scanning probe microscopy techniques and macroscopic ferroelectric measurements, the single phase HZO thin films exhibit ferroelectric properties with a remanent polarization of about 20 µC cm−2. Interestingly, the HZO thin film shows ferroelectric resistive switching with an ROFF/RON ratio of about 16 100% with excellent device performance. Furthermore, brain‐like learning behavior is also observed in the HZO thin film. These results may serve to stimulate the study of ferroelectric properties of HZO thin films and their application in the electronic industry.

Brain-inspired computing is an emerging field, which intends to extend the capabilities of information technology beyond digital logic. The progress of the field relies on artificial synaptic devices as the building block for brainlike computing systems. Here, we report an electronic synapse based on a ferroelectric tunnel memristor, where its synaptic plasticity learning property can be controlled by nanoscale interface engineering. The effect of the interface engineering on the device performance was studied. Different memristor interfaces lead to an opposite virgin resistance state of the devices. More importantly, nanoscale interface engineering could tune the intrinsic band alignment of the ferroelectric/metal-semiconductor heterostructure over a large range of 1.28 eV, which eventually results in different memristive and spike-timing-dependent plasticity (STDP) properties of the devices. Bidirectional and unidirectional gradual resistance modulation of the devices could therefore be controlled by tuning the band alignment. This study gives useful insights on tuning device functionalities through nanoscale interface engineering. The diverse STDP forms of the memristors with different interfaces may play different specific roles in various spike neural networks.

We report on the efficient spin-orbit torque (SOT) switching in a single ferromagnetic layer induced by a new type of inversion asymmetry, the composition gradient. The SOT of 6-to 60-nm epitaxial FePt thin films with a L1 0 phase is investigated. The magnetization of the FePt single layer can be reversibly switched by applying electrical current with a moderate current density. Different from previously reported SOTs which either decreases with or does not change with the film thickness, the SOT in FePt increases with the film thickness. We found the SOT in FePt can be attributed to the composition gradient along the film normal direction. A linear correlation between the SOT and the composition gradient is observed. This Rapid Communication introduces a platform to engineer large SOTs for lower-power spintronics.

Spin-orbit torque (SOT) offers promising approaches to developing energy-efficient memory devices by electric switching of magnetization. Compared to other SOT materials, metallic antiferromagnet (AFM) potentially allows the control of SOT through its magnetic structure. Here, combining the results from neutron diffraction and spin-torque ferromagnetic resonance experiments, we show that the magnetic structure of epitaxially grown L10-IrMn (a collinear AFM) is distinct from the widely presumed bulk one. It consists of twin domains, with the spin axes orienting toward [111] and [−111], respectively. This unconventional magnetic structure is responsible for much larger SOT efficiencies up to 0.60 ± 0.04, compared to 0.083 ± 0.002 for the polycrystalline IrMn. Furthermore, we reveal that this magnetic structure induces a large isotropic bulk contribution and a comparable anisotropic interfacial contribution to the SOT efficiency. Our findings shed light on the critical roles of bulk and interfacial antiferromagnetism to SOT generated by metallic AFM.

Out-of-plane ferroelectricity with a high transition temperature in nanometer-scale films is required to miniaturize electronic devices. Direct visualization of stable ferroelectric polarization and its switching behavior in atomically thick films is critical for achieving this goal. Here, ferroelectric order at room temperature in the two-dimensional limit is demonstrated in tetragonal BiFeO3 ultrathin films. Using aberration-corrected scanning transmission electron microscopy, we directly observed robust out-of-plane spontaneous polarization in one-unit-cell-thick BiFeO3 films. High-resolution piezoresponse force microscopy measurements show that the polarization is stable and switchable, whereas a tunneling electroresistance effect of up to 370% is achieved in BiFeO3 films. Based on first-principles calculations and Kelvin probe force microscopy measurements, we explain the mechanism of polarization stabilization by the ionic displacements in oxide electrode and the surface charges. Our results indicate that critical thickness for ferroelectricity in the BiFeO3 film is virtually absent, making it a promising candidate for high-density nonvolatile memories.