As an antisymmetric exchange interaction, the Dzyaloshinskii-Moriya interaction (DMI) favors canted spin alignment and stabilizes chiral spin textures. However, the existing DMI effects, e.g., interfacial DMI, bulk DMI, and interlayer DMI, cannot achieve long-range characteristics and vertical chirality simultaneously, hindering the implementation of three-dimensional (3D) topological magnetic textures. Here, we first achieve a bulk-like interlayer DMI (BIL-DMI) effect in gradient magnetic multilayers by engineering in-plane (IP) and out-of-plane (OOP) symmetry breaking, which presents unprecedented long-range vertical chirality. The direction and magnitude of the BIL-DMI-induced IP/OOP DMI effective fields depend on the DMI gradient, and the OOP effective field exhibits exotically linear dependence on external magnetic fields, distinctly different from the existing saturation behaviors of interlayer DMI. Moreover, a continuum model is built to explain the mechanism of BIL-DMI and quantitatively describe the experimental observations. Based on the BIL-DMI, unique 3D transverse skyrmion/bimeron strings applicable to next-generation magnonic circuits are first stabilized in theory, which is unachievable relying on existing DMI effects. The discovery of BIL-DMI achieves access to a long-range version of IL-DMI through gradient engineering, providing a platform for the investigation and application of 3D topological magnetic textures.

The nonlinear Hall effect (NLHE), an emergent phenomenon in noncentrosymmetric systems, enables the generation of a transverse voltage without an external magnetic field through a second-order electrical response. However, achieving a sizable NLHE signal remains a critical challenge for its application in frequency-doubling and rectifying devices. Here, we report a light-induced giant enhancement of the NLHE in the 2D electron gas (2DEG) at the CaZrO3/KTaO3 (111) interface. Under illumination, the second harmonic Hall voltage increases substantially and undergoes a sign reversal. Correspondingly, the second-order transverse conductivity (σ(2) yxx) increases by nearly five orders of magnitude, reaching 2.4 µm V-1 Ω-1, while also reversing its sign. Scaling analysis identifies skew scattering as the dominant mechanism, which is highly tunable via optical gating. Photoexcitation pumps electrons from in-gap states into the Ta 5d conduction band, generating high-mobility photocarriers that increase the cubic scattering time (τ3) and thereby, dramatically boost σ(2) yxx. First-principles calculations further reveal that the Berry curvature triple changes sign as the Fermi level approaches the higher-lying Lz,+ subbands, in the Ta 5d accounting for the observed sign reversal. Our work offers a new strategy to optically control the NLHE in oxide 2DEG systems, highlighting the tunability of nonlinear transport by optical excitation.

Bilinear magnetoresistance (BMR), exhibiting a linear response to magnetic field or applied current, has garnered significant attention in recent research. While most previous works have focused on isotropic BMR, arising from isotropic band structure or the spin Hall effect, we report on a strongly anisotropic BMR (ABMR) observed at the KTaO3 Rashba interface, characterized by a unique low-symmetry Fermi surface. For the first time, we have successfully achieved significant regulation of ABMR through the application of gate voltage. Our quantified analysis reveals a profound link between the tunable anisotropy in Rashba spin splitting and the precise modulation of the Fermi level filling, highlighting its central role in governing gate-modulated ABMR. Additionally, we introduce a rigorous physical model that provides a deep and nuanced understanding of the mechanisms underlying gate-voltage-controlled ABMR. This control over electronic processes in low-dimensional systems holds immense potential for both fundamental physics research and the development of advanced multi-channel spintronic devices.

Transition metal oxides with strong spin-orbit coupling exhibit efficient charge-to-spin interconversion. The modification of crystal structure provides a promising platform for enhancing the spin-orbit torque (SOT) efficiency, which potentially leads to energy-efficient spintronic devices. Here, efficient switching of perpendicular magnetization driven by SOT in CaRuO3 films is reported. By precisely tuning octahedral tilt/rotation, the enhancement of SOT efficiency is achieved, and the corresponding spin Hall conductivity can be increased from the value of 2.48 to 7.56 x (& hbar;/2e) x 104 Omega-1 m-1. The thickness dependence of spin Hall conductivity indicates that SOT originates from the bulk spin Hall effect. Moreover, this large SOT efficiency contributes to the reduction of power consumption in current-induced switching of magnetization. The results provide a route to further enhance the SOT efficiency and verify CaRuO3 as a very promising candidate material for efficient spintronics devices.

Exploring the intricate interplay between magnetism and superconductivity is crucial for unveiling the underlying mechanisms of unconventional superconductivity. Here, we report on the magnetotransport evidence for the coexistence of a two-dimensional (2D) superconducting state and a 2D ferromagnetic state at the interface between amorphous CaZrO3 film and (111)-oriented KTaO3 single crystal. Remarkably, the fingerprint of ferromagnetism, i.e., hysteretic magnetoresistance loops, is observed in the superconducting state. The butterfly-shaped hysteresis with twin peaks emerges against the background of superconducting zero resistance, and the peak amplitude increases with the sweep rate of the magnetic field, indicating that the magnetization dynamics are at play in the superconducting state. Moreover, the magnetoresistance hysteresis is strongly dependent on temperature, achieving a maximum near the superconducting transition temperature. This behavior is well described by the thermal activated phase slip model. Density function theory (DFT) calculations suggest that the magnetic moment is primarily contributed by the Ta 5dyz orbital, and the Stoner ferromagnetism is identified. Our findings provide new insights into the interaction of magnetism and superconductivity at KTaO3-based oxide heterointerfaces.

Artificial oxide heterostructures provide valuable opportunities for tailoring interfacial magnetic coupling, which is a central topic of spintronics. In this work, the antiferromagnetic interfacial magnetic coupling is demonstrated in EuO/KTaO3 (001) heterostructures by introducing a LaTiO3 (LTO) buffer layer. Depth-resolved polarized neutron reflectometry reveals that ferromagnetic EuO induces magnetism in the adjacent LTO buffer layer and the interfacial KTaO3 (KTO) through the magnetic proximity effect (MPE). Remarkably, the introduction of the LTO buffer layer at the EuO/KTO interface results in antiparallel alignment between the interfacial KTO layer and EuO, indicating proximity-induced antiferromagnetic coupling across the spacer layer. Anomalous Hall effect and hysteretic magnetoresistance measurements indicate the presence of spin-polarized 2D electron gases in the interfacial layer of KTO. The maximum thickness of the LTO buffer layer for EuO to be able to magnetize KTO is 8 uc (approximate to 3.2 nm), beyond which no hysteretic magnetoresistance is observed. Density functional theory calculations suggest that antiferromagnetic coupling lowers the system energy in LTO-buffered EuO/KTO heterostructure, corroborating the experimental findings. This work highlights the crucial role of interface engineering in controlling interfacial magnetic coupling, providing novel pathways for designing advanced spintronic devices.

The free-field switching of the perpendicular magnetization by the out-of-plane polarized spin current induced spin-orbit torque makes it a promising technology for developing high-density memory and logic devices. The materials intrinsically with low symmetry are generally utilized to generate the spin current with out-of-plane spin polarization. However, the generation of the out-of-plane polarized spin current by engineering the symmetry of materials has not yet been reported. Here, we demonstrate that paramagnetic CaRuO3 films are able to generate out-of-plane polarized spin current by engineering the crystal symmetry. The non-uniform oxygen octahedral tilt/rotation along film’s normal direction induced by oxygen octahedral coupling near interface breaks the screw-axis and glide-plane symmetries, which gives rise to a significant out-of-plane polarized spin current. This spin current can drive field-free spin-orbit torque switching of perpendicular magnetization with high efficiency. Our results offer a promising strategy based on crystal symmetry design to manipulate spin current and could have potential applications in advanced spintronic devices. The authors realize generation of out-of-plane polarized spin current in perovskite oxide CaRuO3 with reduced crystal symmetry by engineering the oxygen octahedra, which can drive efficient field-free switching of perpendicular magnetization.

Due to the strong interlayer coupling between multiple degrees of freedom, oxide heterostructures have demonstrated exotic properties that are not shown by their bulk counterparts. One of the most interesting properties is ferromagnetism at the interface formed between "nonferromagnetic" compounds. Here we report on the interfacial ferromagnetic phase induced in the superlattices consisting of the two paramagnetic oxides CaRuO3 (CRO) and LaNiO3 (LNO). By varying the sublayer thickness in the superlattice period, we demonstrate that the ferromagnetic order has been established in both CaRuO3 and LaNiO3 sublayers, exhibiting an identical Curie temperature of ∼75 K. The X-ray absorption spectra suggest a strong charge transfer from Ru to Ni at the interface, triggering superexchange interactions between Ru/Ni ions and giving rise to the emergent ferromagnetic phase. Moreover, the X-ray linear dichroism spectra reveal the preferential occupancy of the d3z2-r2 orbital for the Ru ions and the dx2-y2 orbital for the Ni ions in the heterostructure. This leads to different magnetic anisotropy of the superlattices when they are dominated by CRO or LNO sublayers. This work clearly demonstrates a charge-transfer-induced interfacial ferromagnetic phase in the whole ferromagnet-free oxide heterostructures, offering a feasible way to tailor oxide materials for desired functionalities.

Due to the strong interactions from multiple degrees of freedom at the interfaces, electron-correlated oxide heterostructures have provided a promising platform for creating exotic quantum states. Understanding and controlling the coupling effects at the oxide interface are prerequisites for designing emergent interfacial phases with desired functionalities. Here, we report the dimensional control of the interface coupling-induced ferromagnetic (FM) phase in perovskite-CaRuO 3 /infinite-layered-SrCuO 2 superlattices. Structural analysis reveals the occurrence of chain-type to planar-type structural transitions for the SrCuO 2 layer as the layer thickness increases. The Hall and magnetoresistance measurements indicate the appearance of an interfacial FM state in the originally paramagnetic CaRuO 3 layers when the CaRuO 3 layer is in proximity to the chain-type SrCuO 2 layers; this superlattice has the highest Curie temperature of ~75 K and perpendicular magnetic anisotropy. Along with the thickness-driven structural transition of the SrCuO 2 layers, the interfacial FM order gradually deteriorates and finally disappears. As shown by the X-ray absorption results, the charge transfer at the CaRuO 3 /chain-SrCuO 2 and CaRuO 3 /plane-SrCuO 2 interfaces are different, resulting in dimensional control of the interfacial magnetic state. The results from our study can be used to facilitate a new method to manipulate interface coupling and create emergent interfacial phases in oxide heterostructures.

Charge-to-spin conversion is crucial for the application of emerging spintronic devices. A two-dimensional electron gas (2DEG) at a complex oxide interface usually possesses strong Rashba spin-orbit coupling, and spin-momentum locking offers a great possibility for efficient charge-to-spin conversion through the Rashba-Edelstein effect. Here, we report the fabrication of metallic 2DEGs in gamma -Al2O3/KTaO3 spinel/perovskite heterostructures and investigate the charge-to-spin conversion for Py/gamma -Al2O3/KTaO3 devices using the technique of spin-torque ferromagnetic resonance. The sizable spin splitting of the band structure results in a large current-induced spin-orbit torque efficiency with values up to around 3.6 at 5 K and about 1.1 at 300 K, which are more than an order of magnitude higher than those of heavy metals (0.07 for Pt at 300 K). Moreover, both theoretical and experimental results show that the charge-to-spin conver-sion is strongly dependent on the position of the Fermi level. These results demonstrate that optimizing the band filling of a KTaO3-based 2DEG is crucial for maximizing the conversion efficiency.

Ferromagnetic materials with a strong spin‐orbit coupling (SOC) have attracted much attention in recent years because of their exotic properties and potential applications in energy‐efficient spintronics. However, such materials are scarce in nature. Here, a proximity‐induced paramagnetic to ferromagnetic transition for the heavy transition metal oxide CaRuO 3 in (001)‐(LaMnO 3 /CaRuO 3 ) superlattices is reported. Anomalous Hall effect is observed in the temperature range up to 180 K. Maximal anomalous Hall conductivity and anomalous Hall angle are as large as ∼15 Ω −1 cm −1 and ∼0.93%, respectively, by one to two orders of magnitude larger than those of the typical 3d ferromagnetic oxides such as La 0.67 Sr 0.33 MnO 3 . Density functional theory calculations indicate the existence of avoid band crossings in the electronic band structure of the ferromagnetic CRO layer, which enhances Berry curvature thus strong anomalous Hall effects. Further evidences from polarized neutron reflectometry show that the CaRuO 3 layers are in a fully ferromagnetic state (∼0.8 μ B /Ru), in sharp contrast to the proximity‐induced canted antiferromagnetic state in 5d oxides SrIrO 3 and CaIrO 3 (∼0.1 μ B /Ir). More than that, the magnetic anisotropy of the (001)‐(LaMnO 3 /CaRuO 3 ) superlattices is eightfold symmetric, showing potential applications in the technology of multistate data storage.

By modifying the entangled multi‐degrees of freedom of transition‐metal oxides, interlayer coupling usually produces interfacial phases with unusual functionalities. Herein, a symmetry‐mismatch‐driven interfacial phase transition from paramagnetic to ferromagnetic state is reported. By constructing superlattices using CaRuO3 and SrTiO3, two oxides with different oxygen octahedron networks, the tilting/rotation of oxygen octahedra near interface is tuned dramatically, causing an angle increase from ≈150° to ≈165° for the RuORu bond. This in turn drives the interfacial layer of CaRuO3, ≈3 unit cells in thickness, from paramagnetic into ferromagnetic state. The ferromagnetic order is robust, showing the highest Curie temperature of ≈120 K and the largest saturation magnetization of ≈0.7 µB per formula unit. Density functional theory calculations show that the reduced tilting/rotation of RuO6 octahedra favors an itinerant ferromagnetic ground state. This work demonstrates an effective phase tuning by coupled octahedral rotations, offering a new approach to explore emergent materials with desired functionalities.

Despite intensive research, the mechanism determining the terahertz (THz) emission of the ferromagnetic (FM) metallic monolayers remains elusive. Here, we report on the results of a systematic investigation on the THz emission generated by pumping Ni80Fe20 monolayers on Al2O3 substrates with a femtosecond laser. We found solid evidence that the THz emission is dominated by the anomalous Nernst effect (ANE), in which a transient spin-polarized charge current can be induced by an ultrafast electron temperature gradient on the picosecond timescale, outputting THz emission. We found a polarity reversal of the THz waveform after the introduction of a SiO2 buffer layer to the sample and found that, based on ultrafast temperature simulation, it was a consequence of direction reversal of temperature gradient. Comparing the THz emission of different FM monolayers further confirms that the THz polarity also strongly depends on the sign of the ANE coefficient. These phenomena unambiguously indicate that the ANE plays a decisive role in the process of THz emission. The present work shows the importance of ultrafast spin caloritronics for a spintronic THz emitter. The principle demonstrated here can be applied to other FM metallic materials.

Magnetic skyrmions are scarcely investigated for single-crystal quality films, for which skyrmions may have a remarkable performance. Even in the limited studies in this aspect, the skyrmions are usually probed by the topological Hall effect, missing important information on dynamic properties. Here, we present a comprehensive investigation on the generation/manipulation of magnetic skyrmions in La0.67Ba0.33MnO3 single-crystal films. Using the technique of magnetic force microscopy, the current-driven skyrmion dynamics are directly observed. Unlike isolated skyrmions produced by magnetic field alone, closely packed skyrmions can be generated by electric pulses in a magnetic background, with a high density (∼60/μm2) and a small size (dozens of nanometers). The threshold current moving skyrmions is ∼2.3 × 104 A/cm2, 2-3 orders of magnitude lower than that required by metallic multilayers or van der Waals ferromagnetic heterostructures. Our work demonstrates the great potential of single-crystal oxide films in developing skyrmion-based devices.

Heterostructure with a symmetry-mismatched interface provides a promising playground for the exploration of emergent phenomena. Herein, we report a systematic investigation on La2/3Sr1/3MnO3/YBaCo2O5+delta (LSMO/YBCO) grown on SrTiO3, a heterostructure formed by perovskite oxides of different symmetry. A high-resolution lattice image shows the formation of high-quality perovskite LSMO and A-site cation-ordered oxygen-deficient double perovskite YBCO, without any signatures of atomic reconfiguration at the interface. Surprisingly, the YBCO-buffered LSMO exhibits perpendicular magnetic anisotropy (PMA), though bare LSMO film is in-plane anisotropic. The PMA is robust, appearing even when the thickness of YBCO is only one unit cell. The typical anisotropy constant is similar to 4 x 10(6) erg cm(-3). X-ray absorption spectroscopy analysis reveals a preferential occupation of the d(3z2-r2dx2-y2), which is confirmed by density functional theory calculations. This orbital reconstruction accounts for the PMA. The formation of a covalent bond between Mn and Co caged by different oxygen polyhedrons, an octahedron and a square pyramid, respectively, stabilizes the orbital reconstruction, resulting in anomalous spin orientation.

Bilinear magnetoresistance (BMR), the magnetoresistance that is linear against either magnetic field or applied current, is a hot topic of recent investigations. While most of the previous works focused on isotropic BMR, here we report on a strongly anisotropic BMR for (110) SrTiO3-based two-dimensional electron gas (2DEG). Remarkably, the BMRmeasured along the [001] axis can be fivefold as large as that obtained along the [110] axis. A close relation is found between BMR and current-induced effective Rashba field, and it is the anisotropy of the Rashba field that causes the anisotropic BMR. Based on the analysis of anisotropic magnetoresistance, effective Rashba fields up to 4.5 T are determined. The band structure of the 2DEG is further calculated, ellipse-shaped Fermi rings are obtained, and the respective effects of different Fermi rings on BMR are distinguished. This work demonstrates the great potential of anisotropic 2DEG for the exploration of unusual effects.

The electric gating on the transport properties of two-dimensional electron gas (2DEG) at the interface of LaAlO 3 /SrTiO 3 (LAO/STO) heterostructure has attracted great research interest due to its potential application in field-effect devices. Most of previous works of gate effect were focused on the LAO/STO heterostructure containing only one conductive interface. Here, we systematically investigated the gate effect on high-quality LAO/STO superlattices (SLs) fabricated on the TiO 2 -terminated (001) STO substrates. In addition to the good metallicity of all SLs, we found that there are two types of charge carriers, the majority carriers and the minority carriers, coexisting in the SLs. The sheet resistance of the SLs with a fixed thickness of the LAO layer increases monotonically as the thickness of the STO layer increases. This is derived from the dependence of the minority carrier density on the thickness of STO. Unlike the LAO/STO heterostructure in which minority and majority carriers are simultaneously modulated by the gate effect, the minority carriers in the SLs can be tuned more significantly by the electric gating while the density of majority carriers is almost invariable. Thus, we consider that the minority carriers may mainly exist in the first interface near the STO substrate that is more sensitive to the back-gate voltage, and the majority carriers exist in the post-deposited STO layers. The SL structure provides the space separation for the multichannel conduction in the 2DEG, which opens an avenue for the design of field-effect devices based on LAO/STO heterostructure.

Heterostructures composed of dissimilar oxides with different properties offer opportunities to develop emergent devices with desired functionalities. A key feature of oxide heterostructures is interface electronics and orbital reconstructions. Here, we combined infinite-layered SrCuO2 and perovskite SrRuO3 into heterostructures. A rare high spin state as large as 3.0 μB f.u-1 and an increase in Curie temperature by 12 K are achieved in an ultrathin SrRuO3 film capped by a SrCuO2 layer. Atomic-scale lattice imaging shows the uniform CuO2-plane-to-RuO5-pyramid connection at the interface, where the regularly arranged RuO5 pyramids were elongated along the out-of-plane direction. As revealed by theoretical calculations and spectral analysis, these features finally result in an abnormally high spin state of the interfacial Ru ions with highly polarized eg orbitals. The present work demonstrates that oxygen coordination engineering at the infinite-layer/perovskite oxide interface is a promising approach towards advanced oxide electronics.

Exploring emergent phenomena in complex oxide heterostructures by interfacial engineering is the frontier of the oxide electronics. The heterointerface formed by oxides with different structures is particularly interesting since symmetry mismatch may produce considerable interface reconstruction and unexpected emergent phenomena. Here, we demonstrate the abnormal magnetic anisotropy in SrFeO2.5/La2/3Ba1/3MnO3/SrFeO(2.5)trilayers that are consisted of the perovskite/brownmillerite heterostructures. The compressively strained La(2/3)Ba(1/3)MnO(3)layer sandwiched between the two SrFeO(2.5)layers exhibits in-plane magnetic anisotropy, while the La(2/3)Ba(1/3)MnO(3)bare film with the same strain state shows perpendicular magnetic anisotropy at low temperature. The high-resolution scanning transmission electron microscope and x-ray absorption spectroscopy analysis reveal the off-center displacement of the Mn ions at interfaces. This would cause a strong orbital reconstruction of Mn ions at the interface and thus the in-plane magnetic anisotropy. This work shows the great potential to explore novel phenomena in artificially designed multilayers by interfacial engineering.