All-electrical switching of a topological non-collinear antiferromagnet at room temperature

Isolated scan unit and scanning tunneling microscope for stable imaging in ultra-high magnetic fields

The high resolution of a scanning tunneling microscope (STM) relies on the stability of its scan unit. In this study, we present an isolated scan unit featuring non-magnetic design and ultra-high stability, as well as bidirectional movement capability. Different types of piezoelectric motors can be incorporated into the scan unit to create a highly stable STM. The standalone structure of scan unit ensures a stable atomic imaging process by decreasing noise generated by motor. The non-magnetic design makes the scan unit work stable in high magnetic field conditions. Moreover, we have successfully constructed a novel STM based on the isolated scan unit, in which two inertial piezoelectric motors act as the coarse approach actuators. The exceptional performance of homebuilt STM is proved by the high-resolution atomic images and dI/dV spectrums on NbSe2 surface at varying temperatures, as well as the raw-data images of graphite obtained at ultra-high magnetic fields of 23 T. According to the literature research, no STM has previously reported the atomic image at extreme conditions of 2 K low temperature and 23 T ultra-high magnetic field. Additionally, we present the ultra-low drift rates between the tip and sample at varying temperatures, as well as when raising the magnetic fields from 0 T to 23 T, indicating the ultra-high stability of the STM in high magnetic field conditions. The outstanding performance of our stable STM hold great potential for investigating the materials in ultra-high magnetic fields.

Temperature-Dependent Spin-to-Charge Conversion and Efficient Manipulation of Elliptical THz Waves in Bi2Te3/TbFeCo Heterostructures

Topological insulators (TIs) with spin-momentum-locked surface states and considerable spin-to-charge conversion (SCC) efficiency are ideal substitutes for the nonmagnetic layer in the traditional ferromagnetic/nonmagnetic (FM/NM) spintronic terahertz (THz) emitters. Here, the TI/ferrimagnetic structure as an effective polarization tunable THz source is verified by terahertz emission spectroscopy. The emitted THz electric field can be separated into two THz components utilizing their opposite symmetry on pump polarization and the magnetic field. TI not only emits a THz electric field via the linear photogalvanic effect (LPGE) but also serves as the medium of SCC via the inverse Edelstein effect (IEE) in the heterostructure. In addition, the amplitude and polarity of the SCC component can be efficiently manipulated by temperature in our ferrimagnetic TbFeCo layer compared with Co or Fe. Once these two THz components are delicately set orthogonally, an elliptical THz wave is generated by the intrinsic phase difference at the THz frequency range. The feasible control of its polarization and chirality is demonstrated by three means: pump polarization, magnetic field, and temperature. These appealing observations may pave the way for the development of elliptical THz wave emitters and polarization-sensitive THz spectroscopy.

Emerging Antiferromagnets for Spintronics

Antiferromagnets constitute promising contender materials for next-generation spintronic devices with superior stability, scalability, and dynamics. Nevertheless, the perception of well-established ferromagnetic spintronics underpinned by spontaneous magnetization seemed to indicate the inadequacy of antiferromagnets for spintronics-their compensated magnetization has been perceived to result in uncontrollable antiferromagnetic order and subtle magnetoelectronic responses. However, remarkable advancements have been achieved in antiferromagnetic spintronics in recent years, with consecutive unanticipated discoveries substantiating the feasibility of antiferromagnet-centered spintronic devices. It is emphasized that, distinct from ferromagnets, the richness in complex antiferromagnetic crystal structures is the unique and essential virtue of antiferromagnets that can open up their endless possibilities of novel phenomena and functionality for spintronics. In this Perspective, the recent progress in antiferromagnetic spintronics is reviewed, with a particular focus on that based on several kinds of antiferromagnets with special antiferromagnetic crystal structures. The latest developments in efficiently manipulating antiferromagnetic order, exploring novel antiferromagnetic physical responses, and demonstrating prototype antiferromagnetic spintronic devices are discussed. An outlook on future research directions is also provided. It is hoped that this Perspective can serve as guidance for readers who are interested in this field and encourage unprecedented studies on antiferromagnetic spintronic materials, phenomena, and devices.

Effective electrical manipulation of a topological antiferromagnet by orbital torques

The electrical control of the non-trivial topology in Weyl antiferromagnets is of great interest for the development of next-generation spintronic devices. Recent studies suggest that the spin Hall effect can switch the topological antiferromagnetic order. However, the switching efficiency remains relatively low. Here, we demonstrate the effective manipulation of antiferromagnetic order in the Weyl semimetal Mn3Sn using orbital torques originating from either metal Mn or oxide CuOx. Although Mn3Sn can convert orbital current to spin current on its own, we find that inserting a heavy metal layer, such as Pt, of appropriate thickness can effectively reduce the critical switching current density by one order of magnitude. In addition, we show that the memristor-like switching behaviour of Mn3Sn can mimic the potentiation and depression processes of a synapse with high linearity-which may be beneficial for constructing accurate artificial neural networks. Our work paves a way for manipulating the topological antiferromagnetic order and may inspire more high-performance antiferromagnetic functional devices.

Tunable Spin Textures in a Kagome Antiferromagnetic Semimetal via Symmetry Design

Kagome antiferromagnetic semimetals such as Mn3Sn have attracted extensive attention for their potential application in antiferromagnetic spintronics. Realizing high manipulation of kagome antiferromagnetic spin states at room temperature can reveal rich emergent phenomena resulting from the quantum interactions between topology, spin, and correlation. Here, we achieved tunable spin textures of Mn3Sn through symmetry design by controlling alternate Mn3Sn and heavy-metal Pt thicknesses. The various topological spin textures were predicted with theoretical simulations, and the skyrmion-induced topological Hall effect, strong spin-dependent scattering, and vertical gradient of spin states were obtained by magnetotransport and magnetic circular dichroism (MCD) spectroscopy measurements in Mn3Sn/Pt heterostructures. Our work provides an effective strategy for the innovative design of topological antiferromagnetic spintronic devices.

High Efficiency and Flexible Modulation of Spintronic Terahertz Emitters in Synthetic Antiferromagnets

Spintronic terahertz (THz) emitters based on synthetic antiferromagnets (SAFs) of FM1/Ru/FM2 (FM: ferromagnet) have shown great potential for achieving coherent superposition and significant THz power enhancement due to antiparallel magnetization alignment. However, key issues regarding the effects of interlayer exchange coupling and net magnetization on THz emissions remain unclear, which will inevitably hinder the performance improvement and practical application of THz devices. In this work, we have investigated the femtosecond laser-induced THz emission in Pt (3)/CoFe (3)/Ru (tRu = 0-3.5)/CoFe (tCoFe = 1.5-10)/Pt (3) (in units of nm) films with compensated and uncompensated magnetic moments. Antiferromagnetic (AF) coupling occurs in the Ru thickness ranges of 0.2-1.1 and 1.9-2.3 nm, with the first peak (tRu = 0.4 nm) of the AF coupling field (Hex) significantly higher than that of the second peak (2.0 nm). Rather high THz amplitude is found for the samples with strong AF coupling. Nevertheless, despite the same remanence ratio of zero, the THz amplitude for the symmetric SAF films declines significantly as the tRu decreases from 0.8 to 0.4 nm, which is mainly ascribed to the noncolinear magnetization vectors due to the increased biquadratic coupling term. Specifically, we demonstrate that an asymmetric SAF structure with a dominant FM layer is more favored than the completely compensated one, which could generate significantly enhanced THz electric field with well-controlled polarity and intensity. In addition, as the temperature decreases, the THz emission intensity increases for the SAF samples of tRu = 0.9 nm with negligible biquadratic coupling, which is contrary to the decreasing trend of the tRu = 0.4 nm sample and has been attributed to the greatly enhanced Hex.

Deterministic Magnetization Switching via Tunable Noncollinear Spin Configurations in Canted Magnets

Spin obit torque (SOT) driven magnetization switching has been used widely for encoding consumption-efficient memory and logic. However, symmetry breaking under a magnetic field is required to realize the deterministic switching in synthetic antiferromagnets with perpendicular magnetic anisotropy (PMA), which limits their potential applications. Herein, we report all electric-controlled magnetization switching in the antiferromagnetic Co/Ir/Co trilayers with vertical magnetic imbalance. Besides, the switching polarity could be reversed by optimizing the Ir thickness. By using the polarized neutron reflection (PNR) measurements, the canted noncollinear spin configuration was observed in Co/Ir/Co trilayers, which results from the competition of magnetic inhomogeneity. In addition, the asymmetric domain walls demonstrated by micromagnetic simulations result from introducing imbalance magnetism, leading to the deterministic magnetization switching in Co/Ir/Co trilayers. Our findings highlight a promising route to electric-controlled magnetism via tunable spin configuration, improve our understanding of physical mechanisms, and significantly promote industrial applications in spintronic devices.