Achieving nonvolatile, all-electric control of spin-dependent transport properties remains a fundamental challenge in spintronics. Here, we demonstrate nonvolatile electric-field-driven control of spin-polarized tunneling in a multiferroic tunnel junction based on a compensated CoGd ferrimagnet. By switching the ferroelectric polarization, we achieve a clear sign inversion of the tunneling magnetoresistance (TMR), clearly indicating the all-electric control of the spin-polarized tunneling. Crucially, the opposite polarity of the TMR sign switching observed above and below the magnetic compensation temperature unambiguously proves that this behavior is intrinsically tied to ferrimagnetism. This phenomenon is governed by a synergistic mechanism: the electric field disparately modulates the antiferromagnetically coupled sublattices while simultaneously driving an interfacial electronic reconstruction that inverts the spin polarization at the Fermi level. Exploiting this intrinsic sublattice asymmetry in ferrimagnets elegantly circumvents traditional magnetic switching paradigms, establishing a framework for next-generation spintronic architectures.

Long-distance transport of magnon spin currents in antiferromagnetic (AFM) insulators has attracted tremendous attention recently, however, the AFM magnon spin relaxation mechanisms remain elusive. Here, we report that the D'yakonov-Perel'-type magnon spin relaxation mechanism governs the spin current transport along the easy axis in two prototypical uniaxial AFM insulators, Cr2O3 and α -Fe2O3. First, an over 450% enhancement of the first-harmonic nonlocal signal induced by a magnetic field is observed prior to the spin-flop transition, which can be well-interpreted by our model incorporating D'yakonov-Perel'-type magnon spin relaxation. Secondly, we find that the magnon spin diffusion length in both crystals increases with magnetic field and saturates at fields above 0.8 T, consistent with our model. Finally, the temperature dependence of the zero-field magnon spin diffusion length in both AFM insulators can be qualitatively explained through our model. These findings are valuable for the development of low-dissipation antiferromagnetic spintronic devices.

Magnetic anisotropy is an important character of magnetic materials, crucial for understanding the fundamental magnetism and unlocking potential applications. Here, epitaxial ferrimagnetic NiCo2O4 (NCO) films were prepared on (001)-, (110)-, and (111)-oriented MgAl2O4 substrates, showing distinct differences in magnetic anisotropy and transport behavior. The (001)-oriented NCO films exhibit a robust perpendicular magnetic anisotropy, whereas the (110) and (111) samples display an in-plane magnetic easy axis. The anomalous Hall effect (AHE) of (001) and (111)-oriented NCO films shows opposite signs, while the AHE of (110)-oriented NCO films exhibits an unusual sign reversal near 150 K, distinguishing other magnetic oxides. These observations can be interpreted in terms of a competition between intrinsic and extrinsic mechanisms for AHE. Based on these findings, NCO films can offer a novel platform for fundamental AHE research: featuring tunable AHE signs and understanding physical mechanisms. Additionally, by introducing an antiferromagnetic NiO layer on NCO films, we achieve an enhanced coercive field and significant exchange-bias field, as a pinned layer, holding immense potential in advanced spintronic devices, such as high-density ferrimagnetic random access memories.

In this work, systematic investigations were conducted to explore the effects and mechanisms of sputtering conditions on the structure and piezoelectric properties of aluminum nitride (AlN) films. Specifically, the contribution of a high-temperature-grown AlN seed layer to the performance of piezoelectric AlN films with molybdenum (Mo) electrodes was demonstrated. Compared with the unseeded AlN/Mo structure, the seeded system exhibited superior crystallization quality, reduced internal stress, and well-maintained surface morphology. Piezoresponse force microscopy measurements revealed a significant enhancement in the piezoelectric coefficient (d(33)) from 0.7 to 6.2 pm/V after incorporating the AlN seed layer. These results indicate that the high-temperature-grown AlN seed layer simultaneously improves both the structural integrity and piezoelectric performance of AlN films on Mo electrodes, providing a novel strategy for the development of high-performance AlN-based microelectromechanical system devices.

Ferroelectric fluorite oxides such as hafnium (HfO2)-based materials are one of the most promising candidates for future large-scale integrated circuits (ICs), while zirconia (ZrO2)-based fluorite materials, which have the same structure as HfO2 and more abundant resources and lower cost of raw materials, are usually thought to be anti- or ferroelectric-like. Here, we report a remanent polarization (Pr) of ∼15 μC/cm2 in orthorhombic ZrO2 thin films at 77 K. This ferroelectricity arises from an electric field-induced antiferroelectric to ferroelectric phase transition, which is particularly noticeable at 77 K. Our work reveals the ferroelectricity in ZrO2 thin films and offers a new pathway to understand the origin of ferroelectricity in fluorite oxides.

NiCo2O4 (NCO), with an inverse spinel structure, stands out for diverse spintronic properties like perpendicular magnetic anisotropy (PMA) and anomalous Hall effect (AHE). Precise control of these properties is essential for ferrimagnetic half-metallic NCO. Here, we report the effective modulation of PMA and AHE in NCO thin films through Fe doping. We demonstrate that the magnetic anisotropy energy (MAE) reaches 1.03 MJ/m3 for NiCo1.6Fe0.4O4 films with a robust PMA at room temperature, an order of magnitude enhancement over pristine NCO films and superior to most known PMA-based magnetic structures. A higher Curie temperature can be obtained in ultrathin NiCo2-xFexO4 films, compared to the pristine NCO films, due to an enhancement of the superexchange interaction from Fe. We also observe the high tunability of AHE in NiCo2-xFexO4 films, with its underlying mechanism undergoing a crossover as x increases, transitioning from extrinsic skew scattering to intrinsic Berry curvature contribution, and finally to a bad-metal-hopping regime. This tunability of AHE is rare in other magnetic systems. These findings provide a pathway for engineering NCO-based ferrimagnetic spintronic platforms with tailored functionalities.

Efforts to combine the advantages of multiple systems to enhance functionalities through solid-solution design present a great challenge due to the constraint imposed by the classical Vegard's law. Here, we successfully navigate this trade-off by leveraging the synergistic effect of chemical doping and strain engineering in the solid-solution system of (1-x)BiFeO3-xBaTiO(3). Unlike bulks, a significant deviation from Vegard's law accompanied by enhanced multiferroism is observed in strained solid-solution epitaxial films, where we achieve a pronounced tetragonality (similar to 1.1), enhanced saturated magnetization (similar to 12 emu/cm(3)), substantial polarization (similar to 107 mu C/cm(2)), and high ferroelectric Curie temperature (similar to 880 degrees C), all while maintaining impressively low leakage current. These characteristics surpass the properties of their parent BiFeO3 and BaTiO3 films. Moreover, the superior ferroelectricity has never been reported in corresponding bulks (e.g., P similar to 5 mu C/cm(2) and T-C similar to 300 degrees C for bulk, with x = 0.5). These findings underscore the potential of strained (1-x)BiFeO3-xBaTiO3 films as lead-free, room temperature multiferroics.

Acidic oxygen evolution reaction (OER) is a major limitation of practical hydrogen production from water electrolysis. Here, we developed an interfacial electron modulation strategy on the basis of Ir-Co3O4 hybrids to build an anomaly OH-rich catalyst-electrolyte layer for efficient OER. Our theoretical studies predict that electron accumulation preferentially occurs on O near Ir sites, which is confirmed via X-ray based and advanced electron microscopy characterization. The accumulated interfacial electron density is up to 20.0 e/& Aring;2 according to the quantification results of integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM) imaging. In-situ Raman results show that the accumulated electron at the interface can promote dissociation of the adsorbed water, and thus generate an OH-rich catalyst-electrolyte layer. The designed IrCo3O4 catalyst exhibits a low overpotential of 200 mV at 10 mA/cm2 in normal three-electrode testing, as well as a high stability for 160 h at 350 mA/cm2 in a proton-exchange membrane electrolyzer. We believed that this developed electron modulation strategy is highly meaningful for rational design of efficient OER catalyst.

Two distinct oxyfluorides were synthesized by annealing a brownmillerite SrCoO2.5 (BM-SCO) thin film in MgF2 powder through soft-chemistry reduction. Throughout the annealing, BM-SCO undergoes two successive phase transitions, which are referred to as perovskite F-doped SrCoOx (P-SCOF) and brownmillerite F-doped SrCoOx (BM-SCOF). P-SCOF retains randomly distributed F-ions, while BM-SCOF forms an F-ordered structure characterized by alternative stacking of square-planar CoO2F2 and octahedral CoO4F2. These three phases could change into each other reversibly under moderate conditions, thereby providing a pathway to extract high-purity F2 with perovskite catalysts.

Ferromagnetic insulators (FMIs) with excellent optical transparency are highly appealing materials for advanced magneto-optical and spintronic devices. However, their applications have been substantially hindered for decades due to the limited availability of FMIs with low Curie temperature Tc and frustrated optical transparency. Herein, we reported that hydrogenated BaFeO2.5 films via facile and effective hydrogen plasma treatment exhibit consecutive structural transformations, accompanying with robust ferromagnetic insulating states with Tc > 400 K and desirable optical transparency with spectral range from visible to infrared. We elucidate the effect of reconfigurations of Fe-O coordinate geometry with distinct crystal structures on the emergent electronic properties of hydrogenated BaFeO2.5 films by combining experimental measurements and theoretical calculations. These findings underscore the importance of engineering polyhedral coordinate of perovskite-derived oxides in surmounting the inherent trade-off between ferromagnetism and electric insulation and open up opportunities for manipulating multifunctional electronic materials.

Perovskite oxides have emerged as compelling contenders for catalyzing the oxygen evolution reaction (OER) due to their low cost, high efficiency, and structural flexibility. Nevertheless, unraveling the intricate structure-activity relationships within correlated oxides remains challenging, impeding the rational design of efficient catalysts. Here, using LaCoO3 epitaxial thin films as a model system, we illustrate a direct correlation between the spin state and OER activity. Through comprehensive investigations via X-ray absorption spectroscopy, scanning transmission electron microscopy, and first-principles calculations, we pinpoint that the enhanced OER activity observed in the tensile-strained films originates from lattice oxygen oxidation triggered by strain-engineered high-spin Co3+. Particularly, the high-spin sites correlated oxygen vacancies during OER lead the reaction into a new pathway, facilitating both the deprotonation of OH* at the metal site and the formation of O-O bonds at the oxygen redox center. Our findings reveal the intricate interplay among strain, spin-state transition, and the transformation of OER mechanism, providing valuable insights for correlated oxide electrocatalysts.

Perovskite oxides have a wide variety of physical properties that make them promising candidates for versatile technological applications including nonvolatile memory and logic devices. Chemical tuning of those properties has been achieved, to the greatest extent, by cation-site substitution, while anion substitution is much less explored due to the difficulty in synthesizing high-quality, mixed-anion compounds. Here, nitrogen-incorporated BaTiO3 thin films have been synthesized by reactive pulsed-laser deposition in a nitrogen growth atmosphere. The enhanced hybridization between titanium and nitrogen induces a large ferroelectric polarization of 70 μC/cm2 and high Curie temperature of ~1213 K, which are ~2.8 times larger and ~810 K higher than in bulk BaTiO3, respectively. These results suggest great potential for anion-substituted perovskite oxides in producing emergent functionalities and device applications.

We demonstrate a terahertz (THz) emitter based on Pt/BiFeO3 heterostructures, leveraging the ultrafast strain-wave-driven spin dynamics for coherent THz generation. Femtosecond laser pulses absorbed in the Pt layer generate elastic strain waves that propagate into the epitaxial BiFeO3 thin films, deflecting the antiferromagnetic Néel vector and exciting out-of-plane spin-wave (magnons) via magnetostriction. These spin waves are converted into ultrafast charge currents through the inverse spin Hall effect in Pt, and then the charge currents excite significant THz radiations. The excitation mechanism, confirmed by polarization-independent emission and a cosine azimuthal dependence, excludes optical nonlinearities and highlights the importance of the interface strain. While electric-field control of THz emission was not experimentally realized, this work establishes Pt/BiFeO3 as a promising platform for nonvolatile, electrically tunable spintronic THz emitters, exploiting the inherent magnetoelectric coupling of multiferroic BiFeO3.

Memristor crossbar arrays, mimicking the human brain, hold immense potential for energy-efficient data-intensive computations in artificial intelligence applications such as image recognition and natural language processing. However, the stochastic nature of resistive switching (RS) in memristors often leads to poor device stability and uniformity, hindering the scalability required for real-world applications. Here, we present a novel phase segregation strategy to achieve uniformly distributed self-assembled Ni nanofilaments within a BaTiO3 matrix, enabling local deterministic redox reactions for RS, as confirmed by comprehensive structural, local, and macroscopic RS studies. This approach yields drastic enhancement in cyclic performance and device uniformity, with the average cyclic variances of Set voltage and low resistance state down to 1.4% and 9.6%, respectively. The devices also exhibit excellent endurance (10(9) cycles) and ultrafast programming speed (down to 100 ns) and achieve over 5-bit level long-term memory states. The enhanced cyclic stability and device uniformity translate to high training and learning accuracies (95%) in a three-level deep neural network, with 1-bit inputs. Our phase segregation strategy provides a generic pathway to overcome the long-standing challenge of device variability in neuromorphic computing.

Understanding the magnetic transitions in van der Waals (vdW) magnets is crucial for their applications in future spintronic devices. While several vdW magnets such as CrI3 and MnBi2Te4 have been extensively studied, the spin reorientation process in CrPS4 under a magnetic field remains unclear. We report here the magnetic transitions of multilayer CrPS4 under both in-plane and out-of-plane magnetic fields as revealed by tunneling magnetoresistance (TMR) measurements. Theoretical calculations based on a linear-chain model combined with experimental data reveal a layer-dependent spin reorientation process. Accompanying the spin reorientation, anomalous kinks appear in the TMR curves, which could be attributed to the spin geometric phase induced interference effect. Our results shed critical light on the magnetic transitions of antiferromagnetic vdW materials, thereby advancing our mechanistic understanding of their behavior.

Tensile biaxial strain has been demonstrated to induce in-plane ferroelectricity in SrTiO3 thin films at room temperature. However, out-of-plane ferroelectricity is more favorable for electronic device applications. Here, we report the achievement of room-temperature out-of-plane ferroelectric SrTiO3 thin films with giant tetragonality (c/a ∼ 1.061) and an ultrahigh ferroelectric stablity temperature (>1000 K) through epitaxial strain and defect engineering. Optical second-harmonic generation (SHG) proves that the enhancement of tetragonality enables improved ferroelectricity. Moreover, a combination of scanning transmission electron microscopy (STEM) and X-ray absorption near-edge spectroscopy (XANES) reveals the origin of enhanced tetragonality and strong ferroelectricity in defect- and strain-codriven supertetragonal SrTiO3 thin films. Our findings present an approach to material design that can be extended to other material systems for the enhancement of ferroelectricity and the observation of emergent phenomena.

AbstractChiral spin textures, as exotic phases in magnetic materials, hold immense promise for revolutionizing logic, and memory applications. Recently, chiral spin textures have been observed in centrosymmetric magnetic insulators (FMI), due to an interfacial Dzyaloshinskii–Moriya interaction (iDMI). However, the source and origin of this iDMI remain enigmatic in magnetic insulator systems. Here, the source and origin of the iDMI in Pt/Y3Fe5O12 (YIG)/substrate structures are deeply delved by examining the spin‐Hall topological Hall effect (SH‐THE), an indication of chiral spin textures formed due to an iDMI. Through carefully modifying the interfacial chemical composition of Pt/YIG/substrate with a nonmagnetic Al3+ doping, the obvious dependence of SH‐THE on the interfacial chemical composition for both the heavy metal (HM)/FMI and FMI/substrate interfaces is observed. The results reveal that both interfaces contribute to the strength of the iDMI, and the iDMI arises due to strong spin−orbit coupling and inversion symmetry breaking at both interfaces in HM/FMI/substrate. Importantly, it is shown that nonmagnetic substitution and interface engineering can significantly tune the SH‐THE and iDMI in ferrimagnetic iron garnets. The approach offers a viable route to tailor the iDMI and associated chiral spin textures in low‐damping insulating magnetic oxides, thus advancing the field of spintronics.

The proliferation of spintronic devices necessitates the advancement of novel material platforms, particularly those featuring ferrimagnetic and antiferromagnetic properties. Among them, NiCo2O4 (NCO), a ferrimagnetic material, stands out for its half-metallic band structure and remarkable attributes like robust perpendicular magnetic anisotropy, a high Curie temperature, and tunable film characteristics through conductivity modulation. These unique features render NCO a prime candidate for spintronics applications. Here, we focus on the orientation-dependent magnetic properties and transport behavior of epitaxial NCO films grown on (001)-, (110)-, and (111)-oriented MgAl2O4 substrates. Notably, NCO films with different epitaxial orientations exhibit significant differences in magnetic anisotropy and transport behavior. Specifically, the (110)-oriented NCO samples present a field-driven spin reorientation transition in the out-of-plane direction, resulting in a split hysteresis loop and corresponding longitudinal magnetoresistance and anomalous Hall curves. Importantly, the anomalous Hall effect (AHE) of (100) and (111)-oriented NCO films displays an opposite sign, while the AHE of (110)-oriented NCO films exhibits an unusual sign reversal at approximately 150 K, distinguishing them from other magnetic oxides. With these findings, NCO films offer a novel platform for fundamental AHE research, featuring tunable AHE signs and intriguing physical mechanisms. Additionally, by introducing an antiferromagnetic NiO layer, we achieve a significant exchange-bias effect and enhanced coercive field, holding immense potential for future spintronics applications, such as ferrimagnetic high-density memories.

The full text of this preprint has been withdrawn by the authors due to author disagreement with the posting of the preprint. Therefore, the authors do not wish this work to be cited as a reference. Questions should be directed to the corresponding author.