Orbital Angular Momentum-Driven Ferromagnetism with Magnetic Anisotropy and Electronic Structure of Epitaxial Neodymium Nitride.

In our information society, the importance of energy conservation is increasing year by year. To tackle this issue, the transition from volatile memory to non-volatile memory can be a solution. One of the candidates for non-volatile memories is a racetrack memory[1], driven by current-induced domain wall motion (CIDWM). For practical use, faster CIDWM and lower threshold current density are key factors. In order to reach this goal, we have been focusing on and investigating Mn4N as a promising material. Mn4N film is an antiperovskite ferrimagnet without rare-earth elements, which is advantageous in fast magnetization reversal due to its perpendicular magnetic anisotropy (Ku ~ 1.1×105 J/m3) and a small saturation magnetization (MS ~ 80 kA/m)[2]. Previous study on 1-2μm-wide Mn4N strips showed the fastest spin-transfer-torque-driven domain wall motion (vDW ~ 900 m/s at 1.3×1012 A/m2) at room temperature (RT)[2], comparable to those reported in the system including rare-earth 4f magnets or heavy metals. To achieve faster vDW, Mn4N based mixed crystals have been studied in pursuit of the use of magnetic and/or angular momentum compensation for more efficient CIDWM thanks to diverged damping constants. Recently, Mn4-xNixN films have been suggested to have a magnetic compensation (MC) point between x = 0.1 and 0.25 at RT[3]. We found that Mn4-xCoxN films have a compensation point between x = 0 and 0.8 from x-ray magnetic circular dichroism (XMCD) measurements[4]. However, there is a lack of information about the magnetic behavior of Mn4-xCoxN at values x much smaller or larger than 0.8. Considering that the compensation in Mn4-xNixN takes place in a small range of composition x, further compensation points can be found when x is far from 0.8. In this work, we performed XMCD measurements on Mn4-xCoxN epitaxial films at x = 0.2 and 1.3 and investigated the change in magnetic structures by composition ratio to verify MC at RT.20-30 nm-thick Mn4-xCoxN films with x = 0-1.3 were epitaxially grown on SrTiO3(001) substrates by molecular beam epitaxy. SiO2 or Ta capping layers were sputtered in-situ on the surface to prevent oxidation. X-ray absorption spectroscopy (XAS) and XMCD measurements were performed at BL-16A of KEK-PF for x = 0.2 and 1.3. In these measurements, we applied an external magnetic field of 5 T perpendicular to sample surfaces. The incidence angle of the circularly polarized x-ray was 54.7°(magic angle) to the plane in order to simplify the sum rule calculation. For x = 0.8, the XMCD measurements were carried out at BL23SU of SPring-8[4].Figures 1(a)-1(c) show the XAS and XMCD spectra of Mn in Mn4-xCoxN at x = 0.2, 0.8[4], and 1.3, respectively. In these figures, the sharp peak near 640 eV comes from Mn atoms at corner sites (I sites), and the broad peak near 643 eV originates from those at face-centered sites (II sites)[4]. We observed the sign reversals of XMCD signals between x = 0.2 and 0.8, and also between x = 0.8 and 1.3. Similar sign reversals were also observed in the XMCD signals of Co atoms. These results indicate that MC occurs twice in the range of x = 0-1.3 in Mn4-xCoxN. Besides, the XAS spectra of Co indicate that Co preferentially occupied the corner sites. We also calculated the mean magnetic moment of Co by using the sum rule analysis. Figure 2 shows the expected magnetic structures derived from the XMCD measurements. Around x = 0.2, Co atoms preferentially replaced Mn(I) and thus the total magnetic moment of I site and that of face-centered site (II site) became closer. With further increasing x, the total magnetic moment became zero. In this manner, the first MC occurred between x = 0.2 and 0.8. After the first MC, the total magnetic moment of II sites became larger and this led to the reversal of magnetic moments of all atoms in order to minimize the Zeeman energy. Above x = 0.8, Co atoms gradually got to occupy II sites and thus the second MC occurs. As far as we investigated, Mn4-xCoxN is the only material which has two MC points at RT. This property can be useful for spintronic devices, for example, the use of compensation in a wide range of composition.The XMCD experiment for x = 0.2 and 1.3 was performed with the approval of the Photon Factory Program Advisory Committee (Proposal No. 2019G574). **

Many 5d transition metal oxides have a unique electronic structure, where the density of states near the Fermi level is dominated by only 5d electrons with strong spin–orbit coupling. IrO2, a Dirac nodal line semi-metal, is the simplest of these oxides. The presence of 5d electrons and gap opening of Dirac nodal lines via strong spin–orbit coupling allows for the hybridization of the 5d electrons of the oxide with the itinerant d electrons of a ferromagnet, while simultaneously increasing the intrinsic spin Hall effect. We report large charge-to-spin conversion in thin films of this material using spin-torque ferromagnetic resonance experiments. By independently performing line shape analysis and linewidth modulation experiments, we conclusively determine the spin Hall angle of optimized IrO2 films to be ∼8 times larger than that of Pt.

Application of renewable energy systems has become very popular. Since most utilities do not track the end points of their distribution lines carefully, where most of the wind turbines are connected to the grid, increasing the application of renewable energies in utilities can result in problems for the whole system dynamics. This paper presents the design and control of a D-STATCOM inverter for small to mid-sized wind turbines (10kW-20kW) to solve the problem of power factor correction of the grid. The proposed D-STATCOM Inverter can control the VARs on each single feeder line while the output of the renewable energy source, especially wind, is varying. Active power is controlled by shifting the phase angle while reactive power control is achieved by modulation index control. Also, the inverter is able to eliminate a large amount of harmonics using the optimized harmonic stepped waveform (OHSW) technique. The proposed inverter utilizes the hybrid-clamped topology. All simulations were done in MATLAB/Simulink environment.

A review of renewable energy applications in buildings in the hot-summer and warm-winter region of China

It is our great pleasure to welcome you to the 2022 3rd International Conference on Smart Grid and Energy Engineering (SGEE 2022), held during November 25th-27th, 2022 in Nanjing, China (virtual conference). The conference is a continuation of the international academic conferences in 2020 and 2021, respectively.The primary goal of SGEE 2022 is to provide an international forum for researcher and practitioner to share ideas in all aspect of how to enhance the vocational capability related to Smart Grid and Energy Engineering under the changing and advancing domestic and international situation. Besides, the conference promoted scientific and academic information interchange among all the participants working all over the world. And it will be held every year to make it an ideal platform for people to share views and experiences in related fields.During the conference, we had about 100 participations both as speakers and participants, including researchers, teachers, students, industrial experts, and professionals. To make this conference on schedule, we had a three-part plenary including a keynote speech delivered by resources persons from different parts of China and other countries. All the keynote speakers have delivered expertise lectures by imparting the latest findings from their respective research domains. Among them, Prof. Yifei Wu from Xi’an Jiaotong University, China addressed a keynote speech on the title Research on Economical DC Interruption Technology. In his presentation, the economical DC interruption technology based on arc voltage enhancement was proposed, in which the complex current commutation module was avoided and reduced the cost and volume by more than 30% compared with the existing schemes. Base on the research, a series of 10kV DC circuit breakers based on arc voltage enhancement have been developed and applied in Jiangsu and other DC distribution demonstration projects. It was a wonderful opportunity for all the participants to interact with the experts and specialists to get their advice or suggestions.The proceedings of SGEE 2022 contain quantities of excellent papers grouped by topics. All submissions were performed double blind review to check their quality of content, level of innovation, significance, originality and legibility, covering but not limited to the following topics: Smart Grid Technologies, Power Transmission and Distribution, Renewable Energy, Electricity and Energy System Applications, etc.We would like to express our gratitude to all the participants for their fruitful work and excellent contribution to the success of SGEE 2022. Especially, we appreciate the enormous work of the editorial board and reviewers in the preparation of this volume. Also, our heartfelt thanks and appreciation go to the Editors and Managers, Journal of Physics: Conference Series for their help and kind cooperation during the preparation of the proceedings. We hope you will benefit from all the manuscripts of the proceedings and learn new and novel ideas.The Committee of SGEE 2022List of Committee member is available in this pdf.

Smart Grids—Renewable Energy, Power Electronics, Signal Processing and Communication Systems Applications

Power electronics technologies have been widely used in renewable energy systems. These energy resources require certain type of power electronic technology to make them in useful formats either through rotational or stationary power conversions. Most renewable energy resources tend to be geographical dependent and clustered in certain areas due to availability of natural resources. This article shows the different types of energy resources and the application of power electronics in different energy resources.

This paper presents a new analytical model for both magnetic flux density and thrust force in a linear direct-drive machine. The model is then used to design a tubular linear direct drive machine (TLDDM) by optimizing its effective parameters. Although the machine has many applications when it works as a motor, but the same design can be used when it works as a generator, where it has applications in renewable energy and sustainable systems. Two-dimensional finite element method (FEM) is used for numerical analysis. Magnetic flux density and thrust force computed numerically shows a good agreement with the values resulted from proposed analytical model. This research, investigates the effect of some geometrical dimensions of Tubular Linear Direct-Drive Machine (TLDDM). The sensitivity analysis of parameters by response surface method (RSM) highlights the influence of effective parameters and their interactions. Permanent magnet (PM) radius, PM length, air gap, coil thickness, and current density of phases are effective factors on Mover’s acceleration. It is found that lower air gap, higher coil thickness and longer PM cause higher ratio of maximum thrust force to mover’s mass. It is shown that RSM can predict the optimum acceleration with error of 6%. The general shape of thrust force in different current densities is also confirmed by experimental results.

Phonon and spintronic structures of monolayered Janus vanadium-dichalcogenide compounds are calculated by the first-principles schemes of pseudopotential plane-wave based on spin-density functional theory, to study dynamic structural stability and electronic spin-splitting due to spin-orbit coupling (SOC) and spin polarization. Geometry optimizations and phonon-dispersion spectra demonstrate that vanadium-dichalcogenide monolayers possess a high enough cohesive energy, while VSTe and VTe2 monolayers specially possess a relatively higher in-plane elastic coefficient and represent a dynamically stable structure without any virtual frequency of atomic vibration modes. Atomic population charges and electron density differences demonstrate that V–Te covalent bonds cause a high electrostatic potential gradient perpendicular to layer-plane internal VSTe and VSeTe monolayers. The spin polarization of vanadium 3d-orbital component causes a pronounced energetic spin-splitting of electronic-states near the Fermi level, leading to a semimetal band-structure and increasing optoelectronic band-gap. Rashba spin-splitting around G point in Brillouin zone can be specifically introduced into Janus VSeTe monolayer by strong chalcogen SOC together with a high intrinsic electric field (potential gradient) perpendicular to layer-plane. The vertical splitting of band-edge at K point can be enhanced by a stronger SOC of the chalcogen elements with larger atom numbers for constituting Janus V-dichalcogenide monolayers. The collinear spin-polarization causes the band-edge spin-splitting across Fermi level and leads to a ferrimagnetic order in layer-plane between V and chalcogen cations with higher α and β spin densities, respectively, which accounts for a large net spin as manifested more apparently in VSeTe monolayer. In a conclusion for Janus vanadium-dichalcogenide monolayers, the significant Rashba splitting with an enhanced K-point vertical splitting can be effectively introduced by a strong SOC in VSeTe monolayer, which simultaneously represents the largest net spin of 1.64 (ћ/2) per unit cell. The present study provides a normative scheme for first-principles electronic structure calculations of spintronic low-dimensional materials, and suggests a prospective extension of two-dimensional compound materials applied to spintronics.

Stirling technology has applications in both renewable energy and waste heat recovery systems. The applicability of Stirling engines in these fields depends on the development of more efficient external combustion machines using renewable energy sources or waste heat. In this study, a new drive mechanism is proposed for the low cost, low weight, low volume and high-efficiency Stirling engines. The effects of the new drive mechanism on the performance parameters of the alpha-type kinematic Stirling engine are investigated, experimentally and theoretically. The mathematical model is validated by using the experimental results. The torque values for different piston forces are presented and compared with that of the conventional slider-crank mechanism. The results show that the torque value of the engine using the new drive mechanism increases by up to 3.66 times compared with that of the conventional slider-crank mechanism.

Considering the difficulty of power supply for automatic observation equipment in the polar regions, this paper introduced a small standalone renewable energy system with wind–solar co-generation as the energy supply scheme. Mathematical models were given, including solar photovoltaic panels, wind turbines, solar irradiance, wind energy density, and renewable energy assessment. ERA-Interim atmospheric reanalysis data were used to evaluate solar energy resources, and the synergistic effect of wind–solar resources on renewable energy was also analyzed and discussed. The system composition of the small standalone renewable energy system was proposed in this study. This system deployed near Zhongshan Station was taken as the object of investigation to analyze the operation performance of each component of the system in different months, and the technical feasibility of the system has also been verified. The results showed that the wind–solar resources in the polar regions had a synergistic effect, which can provide an effective and feasible scheme for the power supply of automatic observation equipment. Through research and analysis, it was found that each component of the renewable energy system, including photovoltaic panels, wind turbines, and batteries, could meet the long-term power supply requirements of automatic observation regardless of the polar periods, polar day or polar night. This paper can not only provide theoretical and data support for the application of small independent renewable energy systems in the polar regions but also provide feasible solutions for clean energy supply of the systems and equipment for independent observation stations deployed in uninhabited islands and alpine regions.

This paper focuses in the optimization of the efficiency of photovoltaic power conversion systems; we present a new alternative for improving both the optimization of the efficiency of photovoltaic power conversion chain. In this way, we present to the valuation problem of photovoltaic by new coupling systems between photovoltaic generators and their loads and performance of photovoltaic (PV) systems and the efficiency of the energy conversion by using different configuration of power converters. Different type’s improvements have been proposed of different architecture in order to choose the correct PV architecture for each PV installation on the efficiency improvement in all power conversion level stages between PV cells and loads. In this context, this work presents the study and adaptive simulation of photovoltaic systems with micro inverters configurations for applications of renewable energy. We performed comparative between a central and distribution connection of converter via an adaptation floor with Maximum Power Point Tracker (MPPT) control. For this reason, it is important to know different types of architecture and different configuration of power converters in order to choose the correct PV architecture for each PV installation. Simulation results are used to demonstrate the proposed topologies to provide improvement in efficiency over existing traditional PV systems.

Due to environmental problems related to using fossil fuels and limitations in the sources of these types of fuels, renewable energies have sharply developed in recent decades. Renewable energy systems are applicable in various fields to provide clean energy. In the current study, medical and dental applications of renewable energies are reviewed. Based on the literature review, technologies based on renewable energy sources can be utilized in medical buildings and instruments. For instance, solar-based technologies can be applied in heating and cooling of hospitals and other healthcare facilities. In addition, the thermal energy of the sun is applicable in autoclaves and medical dryers. Although utilizing renewable energy systems for these applications requires more investment cost and probably more complicated structures, it would result in lower carbon dioxide emission which leads to sustainable development.

ABSTRACTIn this paper, a PLL‐less control technique for single‐phase grid‐connected voltage source converter (VSC) system is proposed that overcomes shortcomings in traditional PLL‐based and existing PLL‐less techniques. The proposed method avoids the use of a PLL and thus significantly decreases the computational complexity of the system as well as enhance system response dynamics for weak grid conditions connected to renewable energy sources. Using the proposed current control technique, the method ensures precise power injection and synchronisation with the grid voltage. Unlike conventional methods that require multiple controllers and complex transformations, the proposed method uses a single proportional‐integral (PI) controller for implementation simplicity, along with better dynamic performance. The main contribution of this study is to use an αβ–dq transformation for reference generation without PLL dependency, enabling robust synchronisation and high‐quality power injection. Performance evaluation results demonstrate the method's satisfactory response time, low total harmonic distortion (THD) and compliance with IEEE power quality standards under varying load and grid conditions. The case and comparative analysis highlight the proposed control method's ability to maintain stability and efficiency, outperforming traditional PLL‐based and other PLL‐less techniques. The study highlights the potential of the PLL‐less approach for applications in renewable energy systems and provides a simplified, reliable and cost‐effective alternative for grid integration. This controller design contributes to the advancement of grid‐tied inverter technology, leading to more efficient use in renewable energy applications for the future.

Single‐stage switched boost inverter (SBI) with buck‐boost capability finds wide applications in renewable energy systems (RES). This paper aims at a comprehensive topological review of various single stage SBI circuits. The boosting techniques of SBI include switched inductor, switched capacitor, and transformer assisted switches. Each SBI derived structure has its own merits and demerits depending on the applications. The performance evaluation of SBIs, based on various perspectives like boost factor, voltage stress across active devices, passive elements count, DC link voltage, switching losses, voltage gain, and efficiency, are also discussed. A suitable modulation strategy is used to obtain the desired boosted and inverted ac output voltage in one stage SBI. Different modulation strategies adopted for SBIs are also included at the end of the topological review. This topological review's contribution enlightens the researchers in selecting appropriate SBI with effective modulation strategies suitable for renewable energy applications. Besides, the benefits and shortcomings of these converters are discussed in detail.