Huali Yang

Spin–orbit torque (SOT) offers a route to compact angular and linear magnetic sensors, but their output is typically lower than conventional magnetoresistance sensors. We extend the SOT-based design to Wheatstone-bridge giant magnetoresistance (GMR) sensors, achieving offset- and hysteresis-free operation. Despite a large GMR ratio, detectivity does not scale directly, highlighting the need to balance sensitivity and working range. By tuning the longitudinal magnetic field to emulate various interlayer-coupling conditions, we map this trade-off, reaching a maximum sensitivity of 5 mV/V/mT, a working range of up to 2.2 mT, and a detectivity of ∼300nT/Hz under optimized conditions. These results establish SOT-enabled linearization in a GMR spin-valve bridge and identify sensing-layer softening, reduced current shunting, and enhanced SOT efficiency as key routes to higher detectivity with lower power consumption.

Equiatomic B2-ordered FeRh alloy possesses unique metamagnetic phase transition above room temperature, which provides a promising route for emerging magnetic recording and spintronic applications when downsized into nanoscale. This paper presents a systematic investigation of magnetic domain in single crystal FeRh films patterned into nanoscale stripe, ring, and circle geometries to explore the evolution of involved transition behavior and magnetic anisotropy. When the characteristic size of the patterns approaches 100 nm, a pronounced supercooling phenomenon occurs; particularly in the circle patterns, the supercooling degree exceeds 15 K. This finding reveals a suppression of the conventional heterogeneity-driven antiferromagnetic nucleation mechanism by dimensional confinement related to the pattern area. Concurrently, the dimensional confinement reduces the demagnetization energy, which enables ferromagnetic FeRh to maintain robust perpendicular magnetic anisotropy up to 390 K and across a wide temperature window of 45 K. Our work not only provides a deep insight into the metamagnetic phase transition mechanism at nanoscale but also is beneficial for realizing novel device functionalities utilizing nanosized FeRh.

Liquid metal nanoparticles (LM NPs) find extensive applications in flexible electronics, nanomedicine, and various other fields owing to their deformability and distinctive solid-liquid core-shell configuration. Nevertheless, the dynamic structural transformations and size-dependent mechanical characteristics of gallium-based core-shell nanoparticles are not well comprehended due to the constraints of high-precision nanoparticle mechanical characterization techniques. This limitation significantly hampers their utilization and advancement. This study systematically investigates the synthesis approaches of thiolated and nonthiolated gallium NPs and comprehensively examines the evolution of their structures and mechanical properties in relation to time and particle dimensions, leading to several significant findings. Initially, scanning electron microscopy revealed the formation of a 3 nm thick gallium oxide (Ga2O3) shell layer on both thiolated and nonthiolated gallium nanoparticles during synthesis. The gallium oxide shells on these two types of nanoparticles did not form simultaneously; instead, they underwent further oxidation and thickening over time, with the thickness stabilizing at day 10 for thiolated NPs and day 15 for nonthiolated NPs. Subsequently, the impact of gallium NPs’ size on mechanical properties, such as elastic modulus and critical fracture force, was investigated using atomic force microscopy and finite element simulation. It was observed that the elastic modulus of gallium NPs increased exponentially as the particle size decreased. This change in modulus was not only solely influenced by Young’s modulus of the gallium oxide shells as predicted by the classical Reissner’s theory but also by the increase in the bulk modulus of the gallium core due to its size effects. A significant discovery was made regarding the impact of internal pressure from the liquid gallium core on preventing the inward buckling of the gallium oxide shell during compression. This discovery notably increased the deformability of gallium nanoparticles, allowing them to withstand strains from 10% to 18% without fracturing. This unique behavior has not been documented in prior studies on the mechanical properties of liquid metal nanoparticles, indicating promising opportunities for utilizing and designing core-shell structured LM NPs.

Magnetic skyrmions are topological spin swirls possessing intriguing electromagnetic properties. The integration of skyrmion materials into flexible substrates has led to the development of flexible spintronics with high performance. However, research into flexible skyrmion materials remains limited. Here, we report the growth of [Pt/Co/Ta]10 multilayer, a typical system hosting skyrmions, on multiple flexible substrates. By combining atomic force microscopy with magnetization measurements, we establish a correlation between surface morphology and perpendicular magnetic anisotropy. The field-driven evolution of skyrmions is also discussed. Additionally, to explain the observed differences in magnetic domain structures of samples grown on flexible substrates and Si substrates, the relationship between magnetic domain width and the variations in magnetic parameters is investigated. Our findings reveal that skyrmion materials can be grown on diverse flexible substrates and tuned by substrate morphology, which shows promising prospects for wearable flexible spintronic devices.

Spin valves have received significant attention in the realm of flexible magnetic materials and devices due to their advantages of rapid response and high integration. Despite these benefits, the practical application of spin valves in wearable devices is constrained by their low stretchability and strain stability under tensile strain. Here, by designing spin valves with zigzag-wrinkled structure, we demonstrated that the magnetotransport properties of our spin valves remained unaffected under 25% biaxial tensile strain, revealing stretchability and strain stability. These outstanding performances are related to the zigzag-wrinkled structure generated after releasing the biaxial pre-strain in PDMS substrates. The flattening of the zigzag wrinkles under biaxial tensile strain releases the direct effect of strain on the metal multilayers, thereby maintaining sensing performances upon stretching. This innovative design paves the way for the development of robust, flexible magnetic devices suitable for wearable technology.

The exchange bias (EB) effect plays an undisputed role in the state‐of‐art spintronic devices, both rigid and flexible. However, the poor stability of EB under mechanical strain is detrimental to the construction of reliable flexible spintronic devices, which poses a great challenge for potential wearable applications. Here, it is revealed that the strain‐induced variation of EB field can be greatly suppressed by engineering flexible IrMn/[Co/Pt]₃ systems featured with perpendicular magnetic anisotropy (PMA). Particularly, in the multi‐stacks with strong PMA, poorly crystallized IrMn structure, and parallel alignment of the ferromagnetic (FM) moments with the biasing magnetic field applied during deposition, an exceptional good strain stability of EB among reported flexible systems is realized, which results from the stable perpendicular FM moments, the low strain transfer efficiency, and the eliminated strain‐driven training effect. These results provide an effective approach to develop flexible spintronic devices with superior strain stability, rendering them strong contenders in the realms of sensor and storage applications.

Elastic polymer-based conductive composites (EPCCs) are of great potential in the field of flexible sensors due to the advantages of designable functionality and thermal and chemical stability. As one of the popular choices for sensor electrodes and sensitive materials, considerable progress in EPCCs used in sensors has been made in recent years. In this review, we introduce the types and the conductive mechanisms of EPCCs. Furthermore, the recent advances in the application of EPCCs to sensors are also summarized. This review will provide guidance for the design and optimization of EPCCs and offer more possibilities for the development and application of flexible sensors.

Dielectric elastomers, such as thermoplastic polyurethanes (TPUs), are widely used as the dielectric layer, encapsulation layer, and substrate of flexible and stretchable devices. To construct capacitors and actuators that work stably upon deformation, it has become urgent to investigate the evolution of dielectricity under stress and strain. However, the lack of effective methods for estimating the dielectric constant of elastomers under strain poses a big challenge. This study reports a device for the in situ measurement of the dielectric constant of TPU under strain. It is found that upon stretching TPU to a strain of 400%, its dielectric constant decreases from 8.02 ± 0.01 to 2.88 ± 0.25 (at 1 MHz). In addition, combined Fourier-transform infrared spectroscopy, the X-ray scattering technique, and atomic force microscopy were utilized to characterize the evolution of the microstructure under strain. The investigation under tensile strain reveals a decreased density and average size of polarized hard domains, along with a tendency of the molecular chains to align in parallel with the tensile stress. The evolution of the microstructures results in a reduction in the measured dielectric constant in TPU.