For ultrafast magnetization switching devices, critical slowing down in conventional ferromagnets near their Curie temperature constitutes a key challenge that must be overcome. In contrast to this typical behavior, we observe an anomalous acceleration of demagnetization in CaRuO_3/SrTiO_3 superlattices, a moderately correlated weak itinerant ferromagnet. The demagnetization rate increases with rising temperature, pump fluence, and applied magnetic field. To explain these anomalous phenomena, we develop a phenomenological model integrating the three-temperature model with self-consistent renormalization theory. Because the intrinsic gradient magnetism of the superlattice suppresses the typical divergence of specific heat, the conventional thermodynamic bottleneck is bypassed. Our model reveals that this decoupling enables the ultrafast dynamics to be predominantly governed by the spin-fluctuation-driven enhancement of the electron-spin scattering vertex. Our work demonstrates how spatial inhomogeneity can decouple macroscopic thermodynamic singularities from microscopic scattering processes, offering a new paradigm for manipulating ultrafast spin dynamics in correlated quantum materials. The pronounced sensitivity of the demagnetization rate to external parameters further suggests the potential for designing highly tunable ultrafast spintronic devices that leverage enhanced fluctuations near the magnetic instability.

The dynamic control of magnon lifetime via magnon-magnon coupling (MMC) is crucial for spintronic applications, yet the underlying mechanisms governing the evolution of dynamical parameters during the coupling process in synthetic antiferromagnets (SAFs) remain elusive. Here, time-resolved polar magneto-optical Kerr effect measurements are employed to investigate the magnon dynamics in a symmetric SAF thin film. By applying a tilted external magnetic field, parity symmetry breaking is induced, leading to the observation of anticrossing gaps in the frequency-field (f-H) dispersion and the emergence of MMC. By tracking the magnon relaxation, abrupt lifetime crossovers are observed near the frequency anticrossing points, and the MMC strength is found to dominate the width of such crossover region. These experimental findings are in good agreement with numerical simulations. A unified physical picture is proposed to account for the lifetime crossovers together with the other two dynamical responses under MMC, all of which constitute key signatures of magnon hybridization. Our study provides direct experimental evidence of MMC-induced mode transformation and demonstrates a viable strategy for manipulating magnon lifetimes in SAF systems.

The switching of conventional magnetization states is a cornerstone of modern spintronics, enabling control over binary ('0' and '1') information bits. Although the coherent control of helicity switching in topological spin configurations is promising for applications such as high-speed multistate memory and neuromorphic and probabilistic computing, realizing it has been challenging. This difficulty stems from the requirement for coherent spin precession while maintaining the intrinsic topology of the spin configurations, which is usually disrupted by conventional excitations. Here we report an experimental realization of coherent helicity toggle switching in nanoscale magnetic vortices occurring on timescales of several hundred picoseconds. This switching behaviour is driven by femtosecond laser pulse excitation under an out-of-plane magnetic field. The mechanism is governed by ultrafast photothermal demagnetization and coherent spin precession in the subsequent remagnetization process, during which the intrinsic topology and symmetry of the vortex are preserved. Crucially, the helicity switching dynamics can be tuned precisely using the laser fluence and magnetic field strength, enabling deterministic to stochastic control over the two energy-degenerate helicity states. This control was reproduced in micromagnetic simulations when the parameters were optimized within a physically reasonable range.

Optical control over magnon creation and annihilation is essential for magnon-based quantum devices. However, conventional optomagnonic processes face a fundamental bottleneck, namely that the probabilities of magnon creation (Stokes scattering) and annihilation (anti-Stokes scattering) are inherently symmetric. Here, we demonstrate that this symmetry can be broken in the canted antiferromagnet Sm0.6Er0.4FeO3 single crystal. We identify two distinct magneto-optical effects in this material that serve as independent channels for magnon-light interactions: magnetic circular birefringence (MCB) facilitates helicity-conserving scattering, while magnetic linear birefringence (MLB) governs helicity-changing scattering. By controlling the coherent interference between MCB and MLB via tuning the linear polarization of light, we selectively suppress either Stokes or anti-Stokes Raman scattering. This selective suppression yields an extreme anti-Stokes-to-Stokes intensity ratio exceeding 20 (13 dB) for quasi-antiferromagnetic (qAFM) magnons, thereby enabling a polarization-selective Raman scattering pathway. We found that the giant precession ellipticity of the antiferromagnetic magnon strongly amplifies the contribution of MLB. Our results extend this effect from previous YIG systems (GHz magnons) into the THz regime. These findings establish rare-earth orthoferrites as a versatile platform for polarization-controlled magnon-light interactions, paving the way for engineering terahertz (THz) antiferromagnetic magnonic devices.

Recently identified altermagnets exhibit a distinctive dual-space nature: they possess spin-split electronic bands akin to ferromagnets in momentum space while maintaining the fully compensated magnetization of antiferromagnets in real space. This inherent duality, originating from the same crystal symmetry, gives rise to various intriguing physical phenomena unique to altermagnets. Consequently, a robust and efficient experimental signature capable of revealing this dual character is critically needed. The magneto-optical Kerr and Voigt effects, given their high sensitivity to ferromagnetism and antiferromagnetism, respectively, are ideally suited to probe this duality. Here, using time-resolved pump-probe magneto-optical measurements, we report the coexistence of pronounced Kerr and Voigt effects in the altermagnet MnTe. Combining the magnetization measurement and first-principles calculations, we demonstrate that the Kerr effect originates from the intrinsic Berry curvature of altermagnetism distribution in momentum space, while the Voigt effect arises from an anisotropic permittivity induced by the in-plane Néel order in real space, directly revealing the dual-space nature of altermagnets. Furthermore, the transient Kerr signal exhibits faster relaxation dynamics than the transient Voigt signal, underscoring their distinct origins in Berry curvature and Néel order, respectively. These findings establish transient magneto-optical responses as distinctive fingerprints of altermagnetism and position altermagnets as promising platforms for manipulating magneto-optical phenomena in ultrafast spin optoelectronics.

The alpha-GeTe is a typical ferroelectric Rashba semiconductor (FERSC) that has attracted a lot of attention in spintronics. The Fe/alpha-GeTe grown on Si substrates has anisotropic Gilbert damping. However, the effect of Al2O3, as another common substrate, remains unknown when alpha-GeTe is grown on it. Here, we fabricated alpha-GeTe thin films using Al2O3 substrates. The alpha-GeTe directly grown on Al2O3 exhibits an in-plane polycrystalline structure. A Bi2Te3 buffer layer can make the alpha-GeTe exhibit a single-crystal feature. The anisotropic Gilbert damping of FM layers is present in Fe/alpha-GeTe/Bi2Te3/Al2O3 and vanished in Fe/alpha-GeTe/Al2O3. Our finding illustrates that alpha-GeTe growth on Al2O3 with a Bi2Te3 buffer layer can serve as a suitable platform for anisotropic research. Our work paves the way for the application of the Al2O3-based alpha-GeTe thin films in anisotropic electronics.

Unsupervised cross-modal hashing has gained increasing attention for its ability to efficiently retrieve semantically relevant data across different modalities without requiring labeled supervision. However, existing methods often suffer from limited feature representation and insufficient semantic alignment due to their reliance on shallow extractors and coarse global features. To address these limitations, we propose a novel method called MGCH (Multi-Granularity feature and Contrastive learning Hashing), which integrates multi-granularity feature learning with contrastive learning under an unsupervised framework. Specifically, MGCH adopts CLIP to extract both global and local features from images and texts. An intra-modal multi-granularity module guides local feature learning via global semantics to enhance fine-grained representation. Furthermore, an inter-modal contrastive learning module is designed using a fusion strategy and Transformer encoder to facilitate deep semantic interaction across modalities. Finally, compact binary hash codes are generated from both intra-modal and inter-modal features for efficient retrieval. Extensive experiments on two benchmark datasets, MIRFlickr-25K and NUS-WIDE, demonstrate that MGCH achieves superior performance over state-of-the-art methods.

Silicon-compatible spintronic terahertz emitters (STEs) are crucial for on-chip ultrafast optoelectronic integration, yet their all-optical controllability remains a key challenge. Here, we fabricate a Ta-buffered CoFeB/Ir heterostructure on Si substrates and realize, for the first time, the enhancement and nonlinear modulation of coherent THz emission under continuous-wave (CW) optical pumping at room temperature. The THz emission, dominated by the inverse spin Hall effect, features an ultrabroad 0-2.5 THz bandwidth and robustness against femtosecond pump fluence and polarization variations. The all-optical modulation of THz generation originates from the competition between photothermal and photodoping effects in the Si substrate. The heterostructure-side pumping with a 450 nm CW laser yields an increased modulation of 46% at 2.546 W cm-2 due to the photothermal effect, while the Si substrate-side pumping at 780 nm leads to 21.3% THz emission suppression by photodoping. Moreover, the THz enhanced modulation efficiency peaks at an Ir layer thickness of 1.2 nm. Our work demonstrates an all-optical controllable Si-based THz source, providing critical insights for the design of next-generation on-chip THz functional devices.

Materials with large spin injection efficiency and long spin relaxation time are highly desirable for spintronic devices with low-power consumption, high-speed operation, and long-distance spin information transmission. With strong spin-orbit coupling (SOC), large spin injection efficiency and spin-charge interconversion can be achieved as an enhancement of damping factor alpha sp induced by spin pumping in ferromagnet/nonmagnetic material heterojunctions, whereas the spin relaxation time (tau s) will be greatly diminished, which makes it contradictory to combine long tau s and large alpha sp in one material. Here, we utilized the topologically protected surface states to enhance damping factor alpha and prolong spin relaxation time tau s simultaneously by delicately altering the thickness of Bi2Te3 in Fe/Bi2Te3 heterostructures. The linear correlation between alpha and tau s is originated from the spin-momentum locking and the robustness against backscattering of topological surface states (TSSs), resulting in a longer tau s even with strong SOC. The interplay between damping factor, spin relaxation, and band structure of topological insulators could shed deep insights on spin relaxation mechanism of TSSs. Our work will provide opportunities on designing spintronic devices for spin-encoded information transmission over macroscopic distances based on topological-band engineering.

The spin pumping in ferromagnet/nonmagnetic materials (FM/NM) heterostructures is an effective technique to inject spin current into NM, which provides the possibility of ultrafast, low-power consumption spintronic devices. Previous work demonstrates that the high order terms in k·p theory can induce a large warping effect, and consequently snowflakelike Fermi contour in topological insulator (TI). Unfortunately, the effect of warped topological surface state (TSS) on pure spin absorption in FM/TI heterostructures is completely unknown. Here, by considering strength of spin accumulation, we identified a mechanism for the anisotropic absorption of spin current in a FM/TI heterostructure with a large warping effect. If the density of states (DOS) of TSS dominates at the Fermi surface, the warping effect results in an anisotropic Gilbert damping at nanosecond timescale and almost isotropic ultrafast demagnetization time at femtosecond timescale. The anisotropy of Gilbert damping is found to decrease as bulk state contributions become more significant in thicker Bi_{2}Te_{3} films. Our theoretical predictions regarding the warping effect-induced spin current absorption at nanosecond and subpicosecond timescales have been experimentally validated in Fe/Bi_{2}Te_{3} heterostructures by ferromagnetic resonance and time-resolved magneto-optical Kerr effect (TRMOKE) results, respectively. Our work provides a more intuitional way to understand the spin transfer mechanism, and lays the groundwork for advancing anisotropic spintronics.

Bit patterned recording(BPR)has attracted much attention due to its promising potential in achieving high densities in magnetic storage devices.The materials with strong perpendicular magnetic anisotropy(PMA)are always preferred in designing the BPR.Here,the patterned Co/Ni multilayers showing d-d hybridization induced PMA was studied.In par-ticular,we record the ultrafast spin dynamics by means of time-resolved scanning magneto-optical Kerr effect(TRMOKE)microscopy.We are able to acquire the"snapshot"magnetic maps of the sample surface because of both the femtosecond temporal and submicrometer spatial resolution in our TRMOKE microscopy.Furthermore,the spatially inhomogeneous ultrafast demagnetization was observed in experiment,and this has been evidenced by simulations.

The conversion of magnons between distinct modes enables advanced nonlinear manipulation of these quasiparticles. Synthetic antiferromagnets (SAFs) with their inherently coupled magnon modes provide a promising platform for such conversion. However, the underlying physical mechanism governing magnon conversion remains to be elucidated. With the micromagnetic simulation, we investigate the nonlinear process of magnon upconversion mediated by second harmonic generation (SHG) in SAFs. We find that the SHG of acoustic mode magnons can act as a driven-field to pump optical mode magnons, enabling efficient energy transfer between them. When the resonance frequency of the acoustic mode is half that of the optical mode magnons, this nonlinear process maximizes the conversion efficiency. Furthermore, coherent control of optical mode population is achieved by synchronizing the phase of SHG-pumping and direct microwave excitation. It provides a mechanism for programmable spin-wave signal processing based on nonlinear magnon conversion, which is the building block for magnonic computing beyond von Neumann architectures.

The complex interplay of magnetic interactions at the yttrium iron garnet(YIG)/ferromagnet interface is important for spintronic and magnonic devices.In this study,we present a comprehensive investigation of the interlayer coupling and switching mechanisms in YIG/Py(permalloy)heterostructures based on gadolinium gallium garnet(GGG)and SiO2 substrates.We observe antiferromagnetic interlayer coupling between Py and YIG on SiO2 substrates,whereas ferromag-netic interlayer coupling is observed on GGG substrates.Using polarized neutron reflectometry with depth-and element-resolved measurements,we obtain an in-depth understanding of the magnetic interactions between the YIG and Py layers.We demonstrate that polycrystalline YIG gives rise to antiferromagnetic interlayer coupling.This work provides valuable insights into designing and controlling magnetic coupling in hybrid structures for spintronic applications.

The China Spallation Neutron Source (CSNS) is designed and constructed by the Institute of High Energy Physics, Chinese Academy of Sciences. The construction of CSNS includes an 80-MeV Linac, a 1.6-GeV Rapid Cycling Synchrotron (RCS), two beam transport lines, a solid target station of 100 kW, three initial neutron instruments and other utility facilities. Based on limited funding and lack of experience in the high-power proton accelerator and the spallation target, the CSNS design was optimized to an advanced user faculty to fulfill the urgent user demand, with a high performance/cost ratio, and to have the capability for the CSNS phase two project (CSNS-II) to increase the beam power to 500 kW with less investment. The CSNS construction started in October 2011, and finished in March 2018 on schedule, and reached the acceptance parameters. Since then, CSNS has been operating efficiently and stably. In March 2024, the proton beam power on the target was increased to 160 kW. More than 1700 user experiments have been carried out so far, indicating a strong user demand. The design, construction and commissioning of CSNS are presented in this paper.

The Rashba effect has emerged as a pivotal phenomenon driving novel discoveries in condensed matter physics. Materials with large Rashba energy E R , wavenumber offset k 0 and Rashba parameter α R are prerequisites for spintronic devices operating above room temperature. While neither ultrathin GeTe films (<3.0 nm thickness) nor monolayer topological insulator Bi 2 Te 3 (1 quintuple layer (QL) on Si(111)) manifest Rashba splitting, An unprecedented strength of Rashba effect with , and in GeTe (1 nm)/Bi 2 Te 3 (1 QL) heterostructure is achieved. The spin‐momentum‐locked bands resulting from the Rashba effect of GeTe /Bi 2 Te 3 is confirmed by density functional theory (DFT) calculations. In GeTe ( x nm)/Bi 2 Te 3 (10 QL), it is find that the values of E R , k 0 and α R significantly enhance as the thickness of GeTe decreases contrasting with GeTe films. By comparing the thickness dependence of GeTe with that of GeTe/Bi 2 Te 3 , it is determined that the enhanced Rashba parameter Δα R is proportional to the electric field in the GeTe/Bi 2 Te 3 heterojunction region. It is concluded that the origin of this huge Rashba effect is attributed to the strong band bending in the GeTe/Bi 2 Te 3 heterojunction region, where the striking inversion‐symmetry‐breaking and significant bandgap difference result in a sharp potential gradient normal to the interface. This work opens an avenue to enhance the Rashba splitting by strong band bending and design spin field effect transistors with spin channel as short as several nanometer scales.

We report large nonreciprocity in the transmission of shear-horizontal surface acoustic waves (SAWs) on LiTaO3 substrate coated with a FeCoSiB/NiFeCu magnetoelastic bilayer. The large difference in saturation magnetization of the two layers not only brings nonreciprocal spin waves (SWs), but also ensures the phonon-magnon (SAWs-SWs) coupling at relatively low wavenumbers. It is found that the angle between the magnetization and the wavevector play important roles in determining the strength of magnetoelastic coupling and nonreciprocity, simultaneously. A large nonreciprocal transmission of SAWs about 30 dB (i.e. 60 dB/mm) is demonstrated at 2.33 GHz. In addition, the dispersion relation between coupled SH-SAWs and nonreciprocal SWs is developed, which provide a good insight into the observed phenomena. Our results offer a convenient approach to implement nonreciprocal SAW isolators or circulators.

The elegant spin physics of Dirac electrons in topological insulators (TIs) have considerably endowed fertile tunability of magnetic/TI heterojunction performance with modified spin-orbit effect engineering. Signatures of proximate hybridization between magnetic states and topological surface states have been reported. However, the nature of the spin relaxation process in these systems remains elusive. Here, we unambiguously demonstrate anisotropic spin relaxation in a spin-orbit-hybridized Fe/Bi2Se3 system. We find a sixfold anisotropy of the Gilbert damping parameter with modulation of up to 33% in Fe/Bi2Se3 in the presence of a topological surface state, together with a sixfold magnetic anisotropy. We anticipate the presence of a spin interplay between the topological spin-orbit texture and magnetic orbital states would manifest an anisotropic Gilbert damping, which corroborates with the density functional theory calculations. It is further demonstrated by the spin Hanle effect indicative of anisotropic spin relaxation time tau s in the adjacent topological layer, inversely scaling with the Gilbert damping factor alpha G. Our findings present an alternative scenario of the anisotropic spin transport process and offer insights into spin manipulation in spin-logic/memory devices utilizing proximity-hybridized Dirac electrons.

(111)-oriented nanotwinned Cu ((111)nt-Cu) has shown its high surface diffusion rate and better oxidation resistance over common polycrystalline Cu (C-Cu). The application of (111)nt-Cu as an interface metallization layer in Ag-sintered technology under the role of oxygen was investigated in this work, and its connecting behavior was further clarified by comparing it with C-Cu. As the sintering temperature decreasing from 300 to 200 °C, the shear strength on the (111)nt-Cu substrate was still greater than 55 MPa after sintering for 10 min. The fracture surface correspondingly changed from the interface of Ag/die to mixed fracture mode, involving the interface of the Ag/Cu substrate and Ag/die. The existence of copper oxide provided a tight connection between Ag and the (111)nt-Cu substrate at all of the studied temperatures. Although lots of small dispersed voids were seen at the interface between copper oxide and (111)nt-Cu at 300 °C, these impurity-induced voids would not necessarily be a failure position and could be improved by adjusting the sintering temperature and time; for example, 200 °C/10 min or heating to 300 °C, and then start cooling at the same time. The microstructure of Ag-Cu joint on (111)nt-Cu behaved better than that on C-Cu. The thinner copper oxide layer and the higher connection ratio of the interface between copper oxide and Ag were still found on the (111)nt-Cu connection’s structure. The poor connection between copper oxide and Ag on C-Cu easily became the failure interface. By controlling the thickness of copper oxide and the content of impurity-induced voids, the use of (111)nt-Cu in advanced-packaging could be improved to a new level.

Ultrafast spin dynamics is the study of the evolution of spin degrees of freedom on a time scale from picoseconds to attoseconds after being excited by an external field.With the development of laser technology,ultrafast spin dynamics has presented new opportunities for realizing ultrafast spintronic devices since 1996.However,despite decades of development,many aspects of femtosecond magnetism remain unclear.Understanding the parameters of these ultrafast spin dynamics processes requires experiments on an even faster timescale.Attosecond magnetism and the interaction of attosecond laser pulses with magnetic materials can reveal spin dynamics on a sub-femtosecond to attosecond time scale.In this review,we first introduce the significant research progress,including the mechanisms of ultrafast demagnetization,all-optical switching,ultrafast spin currents,and terahertz waves.Secondly,we analyze the problems in ultrafast spin dynamics,such as the unclear physical mechanisms of ultrafast demagnetization,the uncertain relationship between magnetic damping and ultrafast demagnetization time,and the unexplored anisotropic ultrafast demagnetization.Thirdly,we discuss the opportunities and challenges in attosecond magnetism.Finally,we analyze and discuss the future development and prospects of ultrafast spin dynamics.

Understanding and manipulating magnetic damping, particularly in magnetic heterostructures, is crucial for fundamental research, versatile engineering, and optimization. Although magnetic damping can be enhanced by the band hybridization between ferromagnetic and nonmagnetic materials at the interface, the contribution of individual subbands on the hybridized bands to magnetic damping is fully unexplored. Here, it is found that magnetic damping αeff is modified by the Fermi level in Fe/GeTe heterostructures via Bi doping. By combining angle-resolved photoemission spectroscopy and density functional theory calculations, the enhancement of damping originated from the strongly hybridized band structures between Fe and the surface Rashba bands of GeTe are unveiled. More interestingly, the Fermi level modulates the density of states (DOS) ratio between the subbands of GeTe and the total DOS of hybridized states, which is directly proportional to the magnetic damping. This work gives an insightful physical understanding of the magnetic damping influenced by the hybridized band structures and opens a novel avenue to manipulate magnetic damping by band engineering.