Weifeng Zhang

A wide range of conductance in artificial synapses is of great significance for regulating electronic properties and realizing neuromorphic computing. In this work, we fabricated a CuInP2S6/graphene (CIPS/G) two-dimensional (2D) heterojunction device for simulating biological neural networks. By combining CIPS with graphene, the tuning range of the synaptic weight is expanded, and the conductance can reach a saturated state more quickly in a pulse operation time of 200 ns. Moreover, the simulation of biological synaptic functions of long-term potentiation/depression is achieved through the update of conductance weights, achieving recognition accuracies of 96.1% and 91.7% in digital recognition and sound feature recognition, respectively. Edge recognition of images is realized using the Bienenstock–Cooper–Munro learning rule. Our 2D heterojunction device shows potential applications in information recognition and image processing.

Neuromorphic computing demands artificial synapses that combine ultra-low energy consumption with simple modulation schemes. Here, we demonstrate unipolar ferroelectric tunnel junction synapse based on an Au/Cr/HZO/LSMO/STO heterostructure, in which both excitatory and inhibitory plasticity are realized solely by tuning the pulse width, without reversing voltage polarity. This unipolar operation further enables emulation of the Bienenstock–Cooper–Munro learning rule with an enhanced depression effect as well as perceptual functions such as edge detection. Pulse-width-modulated long-term potentiation was leveraged to experimentally emulate Pavlovian conditioning. Moreover, continuous long-term potentiation and long-term depression were achieved by alternately varying the pulse width and were applied to motion detection. This work provides a new pathway for implementing diverse neuromorphic functionalities through simple pulse-width modulation, highlighting the potential of unipolar ferroelectric synapses for efficient in-memory computing systems.

Compared to high-symmetry (001)-oriented films, the low-symmetry and anisotropically strained (110)-oriented NiCo2O4 films provide an essential platform for investigating the origins of magnetic anisotropy and the mechanisms underlying the anomalous Hall effect. High-quality epitaxial NiCo2O4 thin films with (110) orientation were grown on MgAl2O4 substrates via off-axis radio frequency magnetron sputtering. The NiCo2O4 films thicker than 2.2 nm exhibit metallic conduction above ∼44 ± 1 K, whereas the 2.2 nm ultrathin films display semiconducting behavior. Robust in-plane ferrimagnetic ordering for the 8.6 nm NCO film is characterized by a saturation magnetization of 2.02 μB/f.u. at 10 K and a Curie temperature of ∼380 K, with field-induced spin reorientation occurring around 6 kOe at 10 K. The anomalous Hall effect exhibits a nonmonotonic temperature dependence, with a sign reversal occurring at 100 K for 8.6 nm films and at 160 K for 6.5 nm films. Notably, resistance fluctuations near the spin reorientation field are observed at low temperatures, attributed to pronounced variations in magnetic domain structures. The scaling relation reveals competition between intrinsic Berry phase contributions and extrinsic scattering mechanisms. These findings underscore the critical role of crystal orientation and strain engineering in tuning the multifunctional properties of NiCo2O4, offering avenues for the design of spintronic devices based on the anomalous Hall effect and magnetic anisotropy.

Heterophase structures of α-Cu₂V₂O₇/β-Cu₂V₂O₇ enhance the photogenerated charge seperation due to energy level matching.

The inverse spinel oxide NiCo2O4, known for its high Curie temperature, low resistivity, and perpendicular magnetic anisotropy, is a promising candidate for the development of next-generation spintronic devices. However, reducing the thickness of the NiCo2O4 film to a few atomic layers degrades its room temperature magnetic and electrical properties, limiting its practical application. In this study, a Co3O4 buffer layer is introduced into ultrathin NiCo2O4 films, which significantly enhances the Curie temperature beyond room temperature and reduces the resistivity, while preserving the strong perpendicular magnetic anisotropy as well as the robust anomalous Hall effect. It is found that the sheet resistance dramatically decreases with the increase in Co3O4 thickness. The observed phenomena may originate from the increased occupation of Ni3+ ions at octahedral sites due to the interfacial coupling, resulting in the intrinsic linear relationship between resistivity and Curie temperature. Additionally, the scaling relation between the anomalous Hall conductivity and longitudinal conductivity highlights the complex interaction between spin-dependent impurity scattering and the band intrinsic Berry curvature. This study indicates that interfacial coupling is an effective strategy for tuning the physical properties of oxides, providing a promising avenue for the application of NiCo2O4-based materials in miniaturized spintronic devices.

Co and Ni codoped strontium ferrite particles were prepared by a solid-state strategy and employed as catalysts for the OER. They exhibited a Tafel slope of 55 mV dec⁻¹ and required an overpotential of 334 mV to afford a current density of 10 mA cm⁻², which is lower than that of Co and Ni separately doped samples. The DFT calculations reveal the redistribution of local charge around Fe atoms, decrease of energy barriers, and increase of conductivity by doping. This work unveils the effect of codoping on the activities of Fe-based perovskite oxide for the OER, providing a strategy to engineer other perovskite-based materials for catalysis.

Hafnium oxide (HfO2)-based ferroelectrics are being explored as potential candidates for ferroelectric memory devices due to their highly compatibility with complementary metal-oxide-semiconductor (CMOS) technology. Enhancing the remanent polarization and investigating the underlying mechanism are crucial tasks. In the present study, tantalum (Ta) was introduced as a dopant to induce ferroelectric properties in HfO2, a large portion of orthorhombic phase was recognized in the as-grown Ta:HfO2 without further thermal treatment. The remanent polarization of Ta:HfO2 thin films can be optimized by adjusting the oxygen flow rates during the sputtering process. The influencing factors for enhanced ferroelectric performance include the control of Ta concentration, its valence state, and the presence of singly ionized oxygen vacancies, which are influenced by oxygen addition. Furthermore, the resistive switching behavior showing non-zero crossing current–voltage (I–V) hysteresis is associated with ferroelectricity and the presence of oxygen vacancies. A model has been proposed to explain the ferroelectric resistive switching with non-zero crossing I–V characteristics by considering the role of oxygen vacancies and polarization effects. This model suggests that the oxygen vacancies at the surface layer, along with ferroelectric polarization, play a crucial role in electron transport.