Nonreciprocal Transport in a Bilayer of MnBi2Te4 and Pt.

MnBi2Te4 (MBT) is the first intrinsic magnetic topological insulator with the interaction of spin-momentum locked surface electrons and intrinsic magnetism, and it exhibits novel magnetic and topological phenomena. Recent studies suggested that the interaction of electrons and magnetism can be affected by the Mn-doped Bi2Te3 phase at the surface due to inevitable structural defects. Here, we report an observation of nonreciprocal transport, that is, current-direction-dependent resistance, in a bilayer composed of antiferromagnetic MBT and nonmagnetic Pt. The emergence of the nonreciprocal response below the Néel temperature confirms a correlation between nonreciprocity and intrinsic magnetism in the surface state of MBT. The angular dependence of the nonreciprocal transport indicates that nonreciprocal response originates from the asymmetry scattering of electrons at the surface of MBT mediated by magnon. Our work provides an insight into nonreciprocity arising from the correlation between magnetism and Dirac surface electrons in intrinsic magnetic topological insulators.

Metastable 1T'-phase group VIB transition metal dichalcogenide crystals.

Metastable 1T'-phase transition metal dichalcogenides (1T'-TMDs) with semi-metallic natures have attracted increasing interest owing to their uniquely distorted structures and fascinating phase-dependent physicochemical properties. However, the synthesis of high-quality metastable 1T'-TMD crystals, especially for the group VIB TMDs, remains a challenge. Here, we report a general synthetic method for the large-scale preparation of metastable 1T'-phase group VIB TMDs, including WS2, WSe2, MoS2, MoSe2, WS2xSe2(1-x) and MoS2xSe2(1-x). We solve the crystal structures of 1T'-WS2, -WSe2, -MoS2 and -MoSe2 with single-crystal X-ray diffraction. The as-prepared 1T'-WS2 exhibits thickness-dependent intrinsic superconductivity, showing critical transition temperatures of 8.6 K for the thickness of 90.1 nm and 5.7 K for the single layer, which we attribute to the high intrinsic carrier concentration and the semi-metallic nature of 1T'-WS2. This synthesis method will allow a more systematic investigation of the intrinsic properties of metastable TMDs.

Electrical Control Grain Dimensionality with Multilevel Magnetic Anisotropy.

In alignment with the increasing demand for larger storage capacity and longer data retention, the electrical control of magnetic anisotropy has been a research focus in the realm of spintronics. Typically, magnetic anisotropy is determined by grain dimensionality, which is set during the fabrication of magnetic thin films. Despite the intrinsic correlation between magnetic anisotropy and grain dimensionality, there is a lack of experimental evidence for electrically controlling grain dimensionality, thereby impairing the efficiency of magnetic anisotropy modulation. Here, we demonstrate an electric field control of grain dimensionality and prove it as the active mechanism for tuning interfacial magnetism. The reduction in grain dimensionality is associated with a transition from ferromagnetic to superparamagnetic behavior. We achieve a nonvolatile and reversible modulation of the coercivity in both the ferromagnetic and superparamagnetic regimes. Subsequent electrical and elemental analysis confirms the variation in grain dimensionality upon the application of gate voltages, revealing a transition from a multidomain to a single-domain state, accompanied by a reduction in grain dimensionality. Furthermore, we exploit the influence of grain dimensionality on domain wall motion, extending its applicability to multilevel magnetic memory and synaptic devices. Our results provide a strategy for tuning interfacial magnetism through grain size engineering for advancements in high-performance spintronics.

Multifunctional Magnetic Oxide-MoS2 Heterostructures on Silicon.

Correlated oxides and related heterostructures are intriguing for developing future multifunctional devices by exploiting their exotic properties, but their integration with other materials, especially on Si-based platforms, is challenging. Here, van der Waals heterostructures of La0.7 Sr0.3 MnO3 (LSMO) , a correlated manganite perovskite, and MoS2 are demonstrated on Si substrates with multiple functions. To overcome the problems due to the incompatible growth process, technologies involving freestanding LSMO membranes and van der Waals force-mediated transfer are used to fabricate the LSMO-MoS2 heterostructures. The LSMO-MoS2 heterostructures exhibit a gate-tunable rectifying behavior, based on which metal-semiconductor field-effect transistors (MESFETs) with on-off ratios of over 104 can be achieved. The LSMO-MoS2 heterostructures can function as photodiodes displaying considerable open-circuit voltages and photocurrents. In addition, the colossal magnetoresistance of LSMO endows the LSMO-MoS2 heterostructures with an electrically tunable magnetoresponse at room temperature. This work not only proves the applicability of the LSMO-MoS2 heterostructure devices on Si-based platform but also demonstrates a paradigm to create multifunctional heterostructures from materials with disparate properties.

Layer-Dependent Interlayer Antiferromagnetic Spin Reorientation in Air-Stable Semiconductor CrSBr.

Magnetic van der Waals (vdW) materials possess versatile spin configurations stabilized in reduced dimensions. One magnetic order is the interlayer antiferromagnetism in A-type vdW antiferromagnet, which may be effectively modified by the magnetic field, stacking order, and thickness scaling. However, atomically revealing the interlayer spin orientation in the vdW antiferromagnet is highly challenging, because most of the material candidates exhibit an insulating ground state or instability in ambient conditions. Here, we report the layer-dependent interlayer antiferromagnetic spin reorientation in air-stable semiconductor CrSBr using magnetotransport characterization and first-principles calculations. We reveal an odd-even layer effect of interlayer spin reorientation, which originates from the competitions among interlayer exchange, magnetic anisotropy energy, and extra Zeeman energy of uncompensated magnetization. Furthermore, we quantitatively constructed the layer-dependent magnetic phase diagram with the help of a linear-chain model. Our work uncovers the layer-dependent interlayer antiferromagnetic spin reorientation engineered by magnetic field in the air-stable semiconductor.

Ultrahigh energy storage in superparaelectric relaxor ferroelectrics.

Electrostatic energy storage technology based on dielectrics is fundamental to advanced electronics and high-power electrical systems. Recently, relaxor ferroelectrics characterized by nanodomains have shown great promise as dielectrics with high energy density and high efficiency. We demonstrate substantial enhancements of energy storage properties in relaxor ferroelectric films with a superparaelectric design. The nanodomains are scaled down to polar clusters of several unit cells so that polarization switching hysteresis is nearly eliminated while relatively high polarization is maintained. We achieve an ultrahigh energy density of 152 joules per cubic centimeter with markedly improved efficiency (>90% at an electric field of 3.5 megavolts per centimeter) in superparaelectric samarium-doped bismuth ferrite­barium titanate films. This superparaelectric strategy is generally applicable to optimize dielectric and other related functionalities of relaxor ferroelectrics.

Phase-controllable growth of ultrathin 2D magnetic FeTe crystals.

Two-dimensional (2D) magnets with intrinsic ferromagnetic/antiferromagnetic (FM/AFM) ordering are highly desirable for future spintronic devices. However, the direct growth of their crystals is in its infancy. Here we report a chemical vapor deposition approach to controllably grow layered tetragonal and non-layered hexagonal FeTe nanoplates with their thicknesses down to 3.6 and 2.8 nm, respectively. Moreover, transport measurements reveal these obtained FeTe nanoflakes show a thickness-dependent magnetic transition. Antiferromagnetic tetragonal FeTe with the Néel temperature (TN) gradually decreases from 70 to 45 K as the thickness declines from 32 to 5 nm. And ferromagnetic hexagonal FeTe is accompanied by a drop of the Curie temperature (TC) from 220 K (30 nm) to 170 K (4 nm). Theoretical calculations indicate that the ferromagnetic order in hexagonal FeTe is originated from its concomitant lattice distortion and Stoner instability. This study highlights its potential applications in future spintronic devices.

Controlling the Magnetic Properties of LaMnO3 /SrTiO3 Heterostructures by Stoichiometry and Electronic Reconstruction: Atomic-Scale Evidence.

Interface-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking are of importance for fundamental physics and device applications. How interfaces affect the interplay between charge, spin, orbital, and lattice degrees of freedom is the key to boosting device performance. In LaMnO3 /SrTiO3 (LMO/STO) polar-nonpolar heterostructures, electronic reconstruction leads to an antiferromagnetic to ferromagnetic transition, making them viable for spin filter applications. The interfacial electronic structure plays a critical role in the understanding of the microscopic origins of the observed magnetic phase transition, from antiferromagnetic at 5 unit cells (ucs) of LMO or below to ferromagnetic at 6 ucs or above, yet such a study is missing. Here, an atomic scale understanding of LMO/STO ambipolar ferromagnetism is offered by quantifying the interface charge distribution and performing first-principles density functional theory (DFT) calculations across this abrupt magnetic transition. It is found that the electronic reconstruction is confined within the first 3 ucs of LMO from the interface, and more importantly, it is robust against oxygen nonstoichiometry. When restoring stoichiometry, an enhanced ferromagnetic insulating state in LMO films with a thickness as thin as 2 nm (5 uc) is achieved, making LMO readily applicable as barriers in spin filters.

Interface Engineering and Emergent Phenomena in Oxide Heterostructures.

Complex oxide interfaces have mesmerized the scientific community in the last decade due to the possibility of creating tunable novel multifunctionalities, which are possible owing to the strong interaction among charge, spin, orbital, and structural degrees of freedom. Artificial interfacial modifications, which include defects, formal polarization, structural symmetry breaking, and interlayer interaction, have led to novel properties in various complex oxide heterostructures. These emergent phenomena not only serve as a platform for investigating strong electronic correlations in low-dimensional systems but also provide potentials for exploring next-generation electronic devices with high functionality. Herein, some recently developed strategies in engineering functional oxide interfaces and their emergent properties are reviewed.

Diffusion and distribution of deuterium in scandium deuteride thin films under irradiation of deuterium ion beam.

Scandium deuteride (ScDx) thin films, as an alternative target for deuterium-deuterium (D-D) reaction, are a very important candidate for detection and diagnostic applications. Albeit with their superior thermal stability, the ignorance of the stability of ScDx under irradiation of deuterium ion beam hinders the realization of their full potential. In this report, we characterize ScDx thin films with scanning electron microscopy (SEM) and X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS) and elastic recoil detection analysis (ERDA). We found with increased implantation of deuterium ions, accumulation and diffusion of deuterium are enhanced. Surprisingly, the concentration of deuterium restored to the value before implantation even at room temperature, revealing a self-healing process which is of great importance for the long-term operation of neutron generator.