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Developments in the design and fabrication of the high saturation magnetization magnetic nanoparticles in the single-domain size regime are highly desirable due to their significant potential for various near-future applications. In this work, we present an in-depth investigation of iron cobalt (Fe65Co35) nanocubes with different sizes covering magnetization configurations from flower to vortex to multidomain states. We synthesized Fe65Co35 nanocubes with tunable edge lengths by adjusting reaction parameters in a liquid-phase reduction reaction. Scanning electron microscope (SEM) images confirm a narrow size distribution. Measured hysteresis loops indicate the size dependence of coercivity and remanence, showing a peak at a size of 17 nm. To explain this phenomenon, a finite element micromagnetic model was used to predict the magnetic properties of Fe65Co35 nanocubes, ranging in size from 10 to 100 nm. Simulation results reveal that the flower-to-vortex transition occurs at around 20 nm, coinciding with the highest coercivity. Larger nanoparticle sizes exhibit a decrease in remanence, with the most significant drop observed between 40 and 60 nm. By combining chemical synthesis and micromagnetic calculations, we have experimentally elucidated the size-dependent spin configurations in Fe65Co35 nanocubes. These findings offer insights for the accurate design and control of spin texture, magnetic remanence, and coercivity in high magnetization nanoparticles. Such advancements can greatly enhance contrast agents for bioimaging, actuators for microelectromechanical (MEMS) systems, and magnetic composites for various applications. 

Abstract To overcome the spatial resolution limit set by aperture-limited diffraction in traditional scanning transmission electron microscopy, microscopists have developed ptychography enabled by iterative phase retrieval algorithms and high-dynamic-range pixel array detectors. Current detector designs are limited by the data rate off chip, so a high-pixel-count detector has a proportionally lower frame rate than the few-segment detectors used for differential phase contrast (DPC) imaging. This slower acquisition speed leads to heightened vulnerability to scan noise, drift, and potential sample damage. This creates opportunities for repurposing fast segmented detectors for ptychography by trading a reduction in reciprocal space pixels for an increase in real space pixels. Here, we explore a strategy of oversampling in real space and instead apply detector pixel upsampling during the reconstruction process. We demonstrate the viability of achieving super-resolution ptychography on thin objects using only 2 × 2 detector pixels, surpassing the resolution of integrated DPC (iDPC) imaging. With optimization using simulated datasets and experiments on MoTe2/WSe2 bilayer moiré superlattices, we achieved super-resolution ptychography reconstructions under rapid acquisition conditions (37.5 pA, 1 μs dwell time), yielding over 50% improvements in contrast and information limit compared to annular dark field and iDPC imaging on the same detectors. 

Abstract The densification of integrated circuits requires thermal management strategies and high thermal conductivity materials 1–3 . Recent innovations include the development of materials with thermal conduction anisotropy, which can remove hotspots along the fast-axis direction and provide thermal insulation along the slow axis 4,5 . However, most artificially engineered thermal conductors have anisotropy ratios much smaller than those seen in naturally anisotropic materials. Here we report extremely anisotropic thermal conductors based on large-area van der Waals thin films with random interlayer rotations, which produce a room-temperature thermal anisotropy ratio close to 900 in MoS 2 , one of the highest ever reported. This is enabled by the interlayer rotations that impede the through-plane thermal transport, while the long-range intralayer crystallinity maintains high in-plane thermal conductivity. We measure ultralow thermal conductivities in the through-plane direction for MoS 2 (57 ± 3 mW m −1  K −1 ) and WS 2 (41 ± 3 mW m −1  K −1 ) films, and we quantitatively explain these values using molecular dynamics simulations that reveal one-dimensional glass-like thermal transport. Conversely, the in-plane thermal conductivity in these MoS 2 films is close to the single-crystal value. Covering nanofabricated gold electrodes with our anisotropic films prevents overheating of the electrodes and blocks heat from reaching the device surface. Our work establishes interlayer rotation in crystalline layered materials as a new degree of freedom for engineering-directed heat transport in solid-state systems.