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Energy efficiency analysis of spin–orbit torque MRAM using composition dependent resistivity and spin Hall angle in Pt/W multilayer structure

Current-induced magnetization switching through spin–orbit torque (SOT) enables low-energy and high-speed switching of magnetic memory (MRAM), positioning SOT-MRAM as a promising candidate for next-generation memory technology. As energy consumption in data computation has become a major challenge in the 21st century, significant efforts have been dedicated to developing energy-efficient memory devices. To optimize SOT-MRAM for energy efficiency, achieving a high spin Hall angle (SHA) has been regarded as essential, as a high SHA indicates efficient spin current generation. However, while previous studies have focused on increasing SHA, this has often led to increased resistivity, which may hinder overall energy efficiency in SOT-MRAM. We propose that resistivity is almost as important as SHA in determining the energy efficiency of SOT-MRAM. In this study, we analyze the effects of both SHA and resistivity in SOT channel materials, which can be modulated by adjusting the composition of Pt and W in Pt/W multilayers. We observed that varying the Pt and W compositions resulted in non-linear changes in both SHA and resistivity, suggesting that evaluating energy efficiency based solely on SHA may be misleading. Thus, we introduce a figure of merit, ξ=ρθSH2, which represents the combined impact of SHA and resistivity on SOT-MRAM energy efficiency. We hope that our findings reveal the importance of considering both SHA and resistivity in the development of energy-efficient SOT-MRAM.

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Dual band angle insensitive metamaterial absorber with MgxCa(0.90−x)Ni0.10Fe2O4 based novel microwave flexible substrate for electromagnetic energy harvesting application

This article presents a metamaterial absorber originated on a flexible substrate of MgxCa(0.90−x)Ni0.10Fe2O4. The MgxCa(0.90−x)Ni0.10Fe2O4 substrate is developed using the sol-gel technique, where X25, X50, and X75 represent 25%, 50%, and 75% of the corresponding material concentration, respectively. The dielectric constant values for X25, X50, and X75 are 2.52, 3.05, and 3.44, with loss tangents of 0.0026, 0.004 25, and 0.0062, respectively. The substrate nanoparticles’ morphology is analyzed using x-ray diffraction, energy dispersive x-ray characterization, and field emission scanning electron microscopy. A metamaterial absorber is then designed on this substrate with a dimension of 16 × 16 mm2. The resonator is comprised of three rings with a square-shaped split outer ring, a square-shaped middle ring, and an innermost arrow-shaped structure. It exhibits absorptance peaks of 99.45% and 99.61% at 4.51 and 7.26 GHz, respectively. Metamaterial and absorber properties are investigated with surface current, electric, and magnetic field analysis. The proposed flexible metamaterial absorber (FMMA) exhibits single negative properties, and it also demonstrates an insensitive response up to 75° for both polarization angle and incident angle variation in transverse electric mode. Furthermore, the FMMA demonstrates exceptionally high energy harvesting (EH) efficiencies of 95.11% and 96.02% at 4.51 and 7.26 GHz, respectively. The efficiency is also investigated for various bending conditions. The small size, lightweight, and flexibility of the structure indicate that MgxCa(0.90−x)Ni0.10Fe2O4 based FMMAs have significant potential for EH applications in the C band.

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All-in-one self-powered wind speed sensor with a wide start-up range and high output power

Anemometers play an important role in environmental monitoring in remote and unique locations, such as forests, islands, and mines. Self-powered wind speed sensors offer a solution for long-term reliable monitoring in unmanned environments. However, current self-powered wind speed sensors suffer from limited integration, limited start-up range, and insufficient output power. Therefore, an all-in-one self-powered wind speed sensor (ASWS-sensor) with a wide start-up range and high output power is proposed. The ASWS-sensor, based on triboelectric nanogenerator and electromagnetic generation technologies, features a unique dual-cup structure that integrates wind speed sensing and wind energy harvesting. This design enables wind speed detection across a broad range from 1.5 to 15 m/s and achieves a high output power of 1.18 W. To meet the long-term, reliable wind speed monitoring needs in coal mine tunnels, a real-time wind speed monitoring and alarm system is developed combining the ASWS-sensor and a master computer. Notably, in this system, the use of the FIR filtering algorithm effectively suppresses significant noise encountered during the collection of single-electrode triboelectric signals with a microcontroller, thereby simplifying the wind speed calculation process. The results show that when the wind speed exceeds 7 m/s, the system can collect, process, wirelessly transmit, analyze, and display wind speed-related data without the need for an external power supply. This demonstrates the excellent application potential of the ASWS-sensor in unmanned monitoring in remote and unique scenarios.

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Thickness-dependent optical properties and ultrafast carrier dynamics of 2D non-layered β-In2S3

Non-layered 2D materials, such as indium sulfide (In2S3), possess distinctive properties due to their unsaturated surface bonds and atomically thin structures, rendering them highly promising for state-of-the-art optoelectronic applications. Herein, we conduct a comprehensive investigation into the optical characteristics and ultrafast carrier dynamics of β-In2S3 nanoflakes. Through thickness-dependent Raman, photoluminescence (PL), and absorption spectra, we reveal the critical role of thickness in tuning the optical properties of β-In2S3. Notably, β-In2S3 exhibits broad PL emission and a robust nonlinear optical response in second-harmonic generation (SHG), largely attributed to inherent defect states. Thickness-dependent SHG surpasses conventional odd/even layer limitations, highlighting β-In2S3’s unique optical versatility. Ultrafast carrier dynamics further unveil two distinct defect-mediated recombination processes: a fast non-radiative pathway and a slower radiative pathway, both accelerating with increasing thickness, as revealed by thickness-dependent transient absorption spectroscopy. This finding underscores the significant modulation of recombination lifetime by varying the thickness of β-In2S3. These insights not only emphasize the versatility of β-In2S3 for optoelectronic applications but also pave the way for its integration into next-generation devices, offering a promising avenue for advancing the field of optoelectronics.

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