Advanced Physics Research最新文献

Graphene/ferromagnet interfaces have widely demonstrated the capability to host peculiar magnetic and electronic properties relevant for spintronic devices. In principle, besides strengthening perpendicular magnetic anisotropy (PMA) and sizable Dzyaloshinskii–Moriya interaction (DMI), graphene provides an additional advantage by acting as a protective layer against oxidation of the underlying metal film. However, the structural imperfections of graphene, often resulting from its growth conditions, can facilitate intercalation, which can compromise the underlying ferromagnetic layer. To address this issue, here, the use of a titania capping layer as a protective barrier for a heterostructure consisting of monolayer graphene grown on a thin cobalt film is proposed. The results demonstrate that the titanium oxide layer does not alter the properties of the interface, as confirmed by X-ray photoemission spectroscopy (XPS) and X-ray magnetic circular dichroism (XMCD) imaging. Furthermore, magneto-optic Kerr effect (MOKE) measurements reveal that the interface's magnetic properties remain stable after prolonged exposure to ambient conditions. Absorption profile simulations show that the capping layer is transparent to visible wavelengths, demonstrating its capability to enable optical studies of atomic interfacial effects without the need for an ultra-high vacuum (UHV) environment. These findings position titanium oxide as a robust, non-invasive capping material for graphene-based spintronic heterostructures.

Control of spin-wave (SW) propagation is demonstrated by introducing a micro-air gap into a nanometer-thick yttrium iron garnet (Y₃Fe₅O₁₂, YIG) microstructure. SWs traverse the gap with reduced intensity following an exponential–linear decay with air gap length, attributed to coupling between incident and reflected dipolar SWs via a time-varying stray magnetic field. By tuning gap length, SW intensity is balanced to address nonreciprocity in counterpropagating magnetostatic surface SWs within an inline interference device. Introducing asymmetric gaps equalizes signal amplitudes and enhances the isolation ratio from 16 to 50 dB, the highest reported for such devices. This approach is applicable to SW-based logic gates and magnetic sensors, with the steep interference profile enabling high sensitivity at room temperature. The air gap also modifies SW transport properties, doubling group velocity from ≈2 km s⁻¹ in the reference device to 4.4 km s⁻¹ for a 66 µm gap at 22 mT, and inducing phase shifts of up to ≈37° for a 1 µm gap change (2–3 µm). These results establish a practical route to high-isolation magnonic interference devices and provide tunable control of group velocity and phase, enabling reconfigurable components such as delay lines and microwave phase shifters.

This study investigates the impact of rare-earth cerium (Ce³⁺) substitution on the structural and electrical properties of cobalt-rich nanoferrites. A series of nanoparticles with the nominal composition Co_0.9Fe_2.1-xCe_xO₄ (where x = 0.0, 0.025, 0.05, 0.075, and 0.1) are synthesized via the sol-gel auto-combustion method. X-ray diffraction (XRD) analysis confirms the formation of a single-phase cubic spinel structure for all compositions, with the lattice parameter systematically increasing from 8.38 to 8.42 Å with rising cerium content, indicating the successful incorporation of the larger Ce³⁺ ions into the lattice. The crystallite size, estimated using the Debye-Scherrer formula, is found to be in the nanometer range. Electron microscopy studies (SEM and TEM) reveal agglomerated, quasi-spherical nanoparticles. The frequency-dependent electrical properties are analyzed at room temperature. Results show a systematic decrease in AC conductivity, dielectric constant (ε'), and dielectric loss tangent (tan δ) with increasing cerium concentration. This behavior is attributed to the substitution of Fe³⁺ ions by Ce³⁺ ions at the octahedral sites, which limits the hopping mechanism between Fe²⁺ and Fe³⁺ ions. The significant reduction in dielectric loss highlights the potential of these cerium-doped nanoferrites for high-frequency device applications.

In the current research work, the anisotropy of the characteristic critical fields and length scales of Sr_{1 − x}K_xFe₂As₂ superconductor by employing the Ginzburg–Landau (GL) phenomenological free energy density functional theory is investigated. Using this model, mathematical expressions are obtained that describe the temperature dependence of the lower, thermodynamic, and upper critical magnetic fields parallel and perpendicular to the c-axis, the GL characteristic parameter, the GL coherence length and GL penetration depth, and the angular dependence of the upper critical magnetic field. Using these mathematical expressions, phase diagrams are plotted using Matplotlib in Python. These phase diagrams show that the characteristic critical magnetic fields—the lower, thermodynamic, and upper critical magnetic fields (both parallel and perpendicular to the c-axis)—and the GL characteristic parameter decrease with increasing temperature and vanish at the superconducting critical temperature (T_C), T_C = 37 K for Sr_{1 − x}K_xFe₂As₂ superconductor. On the other hand, the characteristic length scales—the GL coherence length and GL penetration depth—increase with temperature and diverge at 37 K. The upper critical magnetic field varies with angle (θ). The findings also reveal the anisotropic properties of the lower and upper critical magnetic fields of Sr_{1 − x}K_xFe₂As₂ superconductors.

The nanostructuring of Au thin films induced by ion irradiation is significantly affected by substrate interactions, where processes such as sputtering, diffusion, and dewetting are pivotal in determining the evolution of surface morphology and wettability. The 8 keV Ne ion beam is irradiated on a 10 nm Au thin film on silicon and glass substrates. The surface morphologies of the pristine and irradiated samples are meticulously scrutinized using Atomic Force Microscopy (AFM) to understand the resultant ion irradiation induced Au nanostructures on both substrates. Contact angle measurement and Rutherford Backscattering Spectrometry (RBS) are utilized to explore the wettability of the surface and to determine Au contents on the surface, respectively. The reduction in the peak of RBS is the decrease in Au metal contents on the surface due to ion-induced nuclear sputtering. Wettability of the surface is changed with ion-induced modification in surface morphology. A 2D Detrended Fluctuation Analysis (2D-DFA) is employed to ascertain the Hurst exponent and fractal dimension to understand the wettability and nanostructuring with fractals. The formation of NSs is the result of a dynamic interaction between the processes of nuclear sputtering, dewetting, surface diffusion, and the effect of the morphology of the substrate.

A self-assembled structure designed to mimic magnetotactic bacteria (MTB) by using PEGylated lipid-coated ferrofluid droplet chains dispersed in a thermotropic nematic liquid crystal is presented. This biomimetic structure is compared to live MTBs (M. gryphiswaldense), in terms of structural, functional and dynamic properties. The assembled structure consists of chains of spherical ferrofluid droplets which are significantly larger than the natural MTB magnetosomes that typically display a cuboctahedral chain morphology. Although the self-assembled structure does not achieve the same magnetic coercivity, the presence of a PEGylated lipid coating enhances dispersibility and stability, allowing the formation of long, uniform droplet chains within the liquid crystal medium. Notably, the ferrofluid inclusion in the liquid crystal environment contributes significantly to structural alignment and controlled magnetic responsiveness, suggesting the potential of this self-assembled system in biosensing, targeted delivery, and magnetic-responsive materials.

The emergence of 2D sliding ferroelectric semiconductor expands the ferroelectric materials family and provides an ideal platform for multifunctional applications. Specifically, the non-volatile ferroelectric polarization and bulk photovoltaic effect (BPVE) make them ideal candidates for self-powered photodetection. Photodetectors based on BPVE with a large ferroelectric polarization are highly desirable, due to the combination of high photo-response efficiency and ultrafast response. In this work, the thickness-dependent sliding ferroelectric BPVE and its ultrafast carrier dynamics in 3R-MoS₂ layers are investigated. The sliding ferroelectricity and its associated switchable BPVE response are confirmed at room temperature. With an approximate twofold increase in thickness, a near sevenfold enhancement in short-circuit current, and a tenfold rise in open-circuit voltage are observed, demonstrating an enhanced BPVE. More importantly, due to the enlarged polarization in thicker 3R-MoS₂, time-resolved photocurrent (TRPC) measurements reveal that the log-log slope of the response time versus thickness is less than 2, breaking through the conventional L² (thickness)-dependent limit of the drift-diffusion model, thereby enabling ultrafast response even in thick layers. This work provides a new pathway to high-performance ultrafast bulk photovoltaic photodetectors.

Spanning Clusters and Electrical Conductivity

When fibers are added to a material, isolated clusters begin to interconnect. Once a critical fiber density is reached, a system-spanning network emerges, visibly highlighted here in electric blue, that enables long-range charge transport and determines the material's electrical conductivity. See Research Article 2500040 by Luke Hunter and Sergio Bertazzo for more details.

A Skyrmion Nano-oscillator Operated by Acoustic Waves

This study introduces a skyrmion-based oscillator driven by surface acoustic waves (SAWs) through magnetoelastic coupling. Precise tunability of the oscillator's frequency through varying the strain amplitude induced by a SAW and device dimensions is demonstrated in micromagnetic simulations. The cover image illustrates a skyrmion-based oscillator under the action of a surface acoustic wave. In Research Article 2400206, Jinxing Zhang, Tianxiang Nan and co-workers demonstrate how the proposed design offers a promising pathway for advancing nanoscale microwave frequency converters and spread spectrum modulation technologies.