A Record-High Cryogenic Magnetocaloric Effect Discovered in EuCl Compound.

Adiabatic demagnetization refrigeration (ADR) based on the magnetocaloric effect (MCE) is a promising technique to achieve cryogenic temperature. However, magnetic entropy change (Δ), the driving force of ADR, remains far below theoretical -Δ = ln(2 + 1)/ for most magnetic refrigerants. Here, we report giant MCE in orthorhombic EuCl, where a ferromagnetic ground state with excellent single-ion behavior of Eu and free spins has been demonstrated by combining calculations with Brillouin function analysis and magnetic measurements.

Improved conduction and orbital polarization in ultrathin LaNiO sublayer by modulating octahedron rotation in LaNiO/CaTiO superlattices.

Artificial oxide heterostructures have provided promising platforms for the exploration of emergent quantum phases with extraordinary properties. Here, we demonstrate an approach to stabilize a distinct oxygen octahedron rotation (OOR) characterized by in the ultrathin LaNiO sublayers of the LaNiO/CaTiO superlattices. Unlike the OOR in the LaNiO bare film, the OOR favors high conductivity, driving the LaNiO sublayer to a metallic state of ~100 K even when the layer thickness is as thin as 2 unit cells (u.

Room-Temperature Ferromagnetism with Strong Spin-Orbit Coupling Achieved in CaRuO Interfacial Phase via Magnetic Proximity Effect.

Recently, theoretical and experimental research predicted that ferromagnets with strong spin-orbit coupling (SOC) could serve as spin sources with dramatically enhanced spin-orbit torque (SOT) efficiency due to the combination of spin Hall effect and anomalous Hall effect (AHE), presenting potential advantages over conventional nonmagnetic heavy metals. However, materials with a strong SOC and room-temperature ferromagnetism are rare. Here, we report on a ferromagnetic (FM) interfacial phase with Curie temperature exceeding 300 K in the heavy transition-metal oxide CaRuO, in proximity to LaSrMnO.

Generation of out-of-plane polarized spin current by non-uniform oxygen octahedral tilt/rotation.

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.

Charge-Transfer-Induced Interfacial Ferromagnetism in Ferromagnet-Free Oxide Heterostructures.

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 CaRuO (CRO) and LaNiO (LNO).

Low pressure reversibly driving colossal barocaloric effect in two-dimensional vdW alkylammonium halides.

Plastic crystals as barocaloric materials exhibit the large entropy change rivalling freon, however, the limited pressure-sensitivity and large hysteresis of phase transition hinder the colossal barocaloric effect accomplished reversibly at low pressure. Here we report reversible colossal barocaloric effect at low pressure in two-dimensional van-der-Waals alkylammonium halides. Via introducing long carbon chains in ammonium halide plastic crystals, two-dimensional structure forms in (CH-(CH))NHX (X: halogen element) with weak interlayer van-der-Waals force, which dictates interlayer expansion as large as 13% and consequently volume change as much as 12% during phase transition.

Layered Ferromagnetic Structure Caused by the Proximity Effect and Interlayer Charge Transfer for LaNiO/LaMnO Superlattices.

Magnetic proximity-induced magnetism in paramagnetic LaNiO (LNO) has spurred intensive investigations in the past decade. However, no consensus has been reached so far regarding the magnetic order in LNO layers in relevant heterostructures. This paper reports a layered ferromagnetic structure for the (111)-oriented LNO/LaMnO (LMO) superlattices.

Enhancing Interfacial Ferromagnetism and Magnetic Anisotropy of CaRuO/SrTiO Superlattices via Substrate Orientation.

Artificial oxide heterostructures have provided promising platforms for the exploration of emergent quantum phases with extraordinary properties. One of the most interesting phenomena is the interfacial magnetism formed between two non-magnetic compounds. Here, a robust ferromagnetic phase emerged at the (111)-oriented heterointerface between paramagnetic CaRuO and diamagnetic SrTiO is reported.

Spin-charge interconversion of two-dimensional electron gases at oxide interfaces.

Oxide two-dimensional electron gas (2DEG) is a low-dimensional carrier system formed at the interface of oxide heterojunctions with strong and tunable Rashba spin-orbit coupling which makes oxide 2DEG an ideal platform for converting spin current and charge current. This review provides a summary of the recent advances on the 2DEGs at oxide interfaces for spin-charge interconversion. On one hand, we analyze properties and the efficiency of the spin-to-charge conversion through different ways of spin current injection.

Large Anomalous Nernst Effects at Room Temperature in Fe Pt Thin Films.

Heat current in ferromagnets can generate a transverse electric voltage perpendicular to magnetization, known as anomalous Nernst effect (ANE). ANE originates intrinsically from the combination of large Berry curvature and density of states near the Fermi energy. It shows technical advantages over the conventional longitudinal Seebeck effect in converting waste heat to electricity due to its unique transverse geometry.

Direct Observation of Magnetic Skyrmions and Their Current-Induced Dynamics in Epitaxial Single-Crystal Oxide Films.

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 LaBaMnO single-crystal films.

Classification and Prediction of Skyrmion Material Based on Machine Learning.

The discovery and study of skyrmion materials play an important role in basic frontier physics research and future information technology. The database of 196 materials, including 64 skyrmions, was established and predicted based on machine learning. A variety of intrinsic features are classified to optimize the model, and more than a dozen methods had been used to estimate the existence of skyrmion in magnetic materials, such as support vector machines, -nearest neighbor, and ensembles of trees.

Giant Exchange-Bias-Like Effect at Low Cooling Fields Induced by Pinned Magnetic Domains in Y NiIrO Double Perovskite.

Exchange bias (EB) is highly desirable for widespread technologies. Generally, conventional exchange-bias heterojunctions require excessively large cooling fields for sufficient bias fields, which are generated by pinned spins at the interface of ferromagnetic and antiferromagnetic layers. It is crucial for applicability to obtain considerable exchange-bias fields with minimum cooling fields.

Compressive-Strain-Facilitated Fast Oxygen Migration with Reversible Topotactic Transformation in LaSrCoO via All-Solid-State Electrolyte Gating.

Modifying the crystal structure and corresponding functional properties of complex oxides by regulating their oxygen content has promising applications in energy conversion and chemical looping, where controlling oxygen migration plays an important role. Therefore, finding an efficacious and feasible method to facilitate oxygen migration has become a critical requirement for practical applications. Here, we report a compressive-strain-facilitated oxygen migration with reversible topotactic phase transformation (RTPT) in LaSrCoO films based on all-solid-state electrolyte gating modulation.

Circular Photogalvanic Effect in Oxide Two-Dimensional Electron Gases.

Two-dimensional electron gases (2DEGs) at the LaAlO_{3}/SrTiO_{3} interface have attracted wide interest, and some exotic phenomena are observed, including 2D superconductivity, 2D magnetism, and diverse effects associated with Rashba spin-orbit coupling. Despite the intensive investigations, however, there are still hidden aspects that remain unexplored. For the first time, here we report on the circular photogalvanic effect (CPGE) for the oxide 2DEG.

Enhanced Performance of Δ upon Frequent Alternating Magnetic Fields in FeRh Alloys by Introducing Second Phases.

The cyclability and frequency dependence of the adiabatic temperature change (Δ) under an alternating magnetic field (AMF) are significantly important from the viewpoint of refrigeration application. Our studies demonstrated, by direct measurements, that the cyclability and low-magnetic-field performance of Δ in FeRh alloys can be largely enhanced by introducing second phases. The Δ under a 1.

Self-healing Growth of LaNiO on a Mixed-Terminated Perovskite Surface.

Developing atomic-scale synthesis control is a prerequisite for understanding and engineering the exotic physics inherent to transition-metal oxide heterostructures. Thus, far, however, the number of materials systems explored has been extremely limited, particularly with regard to the crystalline substrate, which is routinely SrTiO. Here, we investigate the growth of a rare-earth nickelate─LaNiO─on (LaAlO)(SrAlTaO) (LSAT) (001) by oxide molecular beam epitaxy (MBE).

Robust Electronic Structure of Manganite-Buffered Oxide Interfaces with Extreme Mobility Enhancement.

The electronic structure as well as the mechanism underlying the high-mobility two-dimensional electron gases (2DEGs) at complex oxide interfaces remain elusive. Herein, using soft X-ray angle-resolved photoemission spectroscopy (ARPES), we present the band dispersion of metallic states at buffered LaAlO/SrTiO (LAO/STO) heterointerfaces where a single-unit-cell LaMnO (LMO) spacer not only enhances the electron mobility but also renders the electronic structure robust toward X-ray radiation. By tracing the evolution of band dispersion, orbital occupation, and electron-phonon interaction of the interfacial 2DEG, we find unambiguous evidence that the insertion of the LMO buffer strongly suppresses both the formation of oxygen vacancies as well as the electron-phonon interaction on the STO side.

Infinite-layer/perovskite oxide heterostructure-induced high-spin states in SrCuO/SrRuO bilayer films.

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 SrCuO and perovskite SrRuO into heterostructures.

Two-dimensional conducting states in infinite-layer oxide/perovskite oxide hetero-structures.

Heterointerfaces sandwiched by oxides of dissimilar crystal structures will show strong interface reconstruction, leading to distinct interfacial effect arising from unusual physics. Here, we present a theoretical investigation on the interfaces between infinite-layer oxide and perovskite oxide (SrCuO/SrTiOand SrCuO/KTaO). Surprisingly, we found well-defined two-dimensional electron gas (2DEG), stemming from atomic reconstruction and polar discontinuity at interface.

Spontaneous Topological Magnetic Transitions in NdCo Rare-Earth Magnets.

Particle-like magnetic textures with nanometric sizes, such as skyrmions, are potentially suitable for designing high-efficiency information bits in future spintronics devices. In general, the Dzyaloshinskii-Moriya interactions and dipolar interactions are the dominant factors for generating nonlinear spin configurations. However, to stabilize the topological skyrmions, an external magnetic field is usually required.

Large Low-Field Magnetoresistance (LFMR) Effect in Free-Standing LaSrMnO Films.

The realization of a large low-field magnetoresistance (LFMR) effect in free-standing magnetic oxide films is a crucial goal toward promoting the development of flexible, low power consumption, and nonvolatile memory devices for information storage. LaSrMnO (LSMO) is an ideal material for spintronic devices due to its excellent magnetic and electronic properties. However, it is difficult to achieve both a large LFMR effect and high flexibility in LSMO films due to the lack of research on LFMR-related mechanisms and the strict LSMO growth conditions, which require rigid substrates.

Electric field control of superconductivity at the LaAlO/KTaO(111) interface.

The oxide interface between LaAlO and KTaO(111) can harbor a superconducting state. We report that by applying a gate voltage ( ) across KTaO, the interface can be continuously tuned from superconducting into insulating states, yielding a dome-shaped - dependence, where is the transition temperature. The electric gating has only a minor effect on carrier density but a strong one on mobility.