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1.
在Heusler 合金Ni-Mn-Ga和NaZn13型化合物La(Fe,Co,M)13, M=Si, Al中很宽温度区间发现巨大磁熵变△S.这两种材料在室温区的磁熵变△S均显著地超过单质稀土Gd并达到著名的磁热效应材料Gd5Si2Ge2合金的磁熵变幅度. Heusler 合金Ni-Mn-Ga中的巨大磁熵变来源于具有一级相变特征的马氏结构相变.NaZn13型化合物La(Fe,Co,M)13, M=Si, Al中异常巨大的磁熵变与合金中的强的磁晶耦合相关,表现为居里温度附近晶格的巨大负膨胀.材料的低价格和其巨大磁熵变表明,Heusler 合金Ni-Mn-Ga和NaZn13型化合物La(Fe,Co,M)13, M=Si, Al在很宽的高温区,尤其在室温区作为磁制冷工质非常有吸引力.  相似文献   

2.
Materials can be ferroelectric, having a spontaneous electric polarization that can be reversed by an external electric field, or they can be ferromagnetic, exhibiting spontaneous magnetization that is switchable by an applied magnetic field. However, until the 1960s, scientists did not expect that these two ferroic properties could co-exist in a single material. Today, materials exhibiting more than one of the primary ferroic properties are called multiferroics. Here, the primary ferroic properties can be ferroelectricity, ferromagnetism, antiferromagnetism, ferroelasticity, ferrotoroidicity or others. Basically, the multiferroic effect originates from the simultaneous breaking of space inversion and time-reversal symmetries. Multiferroics can be imagined as a pas de deux of electricity and magnetism. Recently, National Science Review interviewed Professor Sang-Wook Cheong from Rutgers University, who is one of the pioneering scientists in this field. Cheong talked about the multiferroics field, which has been fast developing since the early 2000s. His introductions and opinions on diverse multiferroic materials and potential multiferroic devices, as well as future research directions, may provide a useful resource for researchers both inside and outside the multiferroic research field.  相似文献   

3.
Mechanically exfoliated two-dimensional ferromagnetic materials (2D FMs) possess long-range ferromagnetic order and topologically nontrivial skyrmions in few layers. However, because of the dimensionality effect, such few-layer systems usually exhibit much lower Curie temperature (TC) compared to their bulk counterparts. It is therefore of great interest to explore effective approaches to enhance their TC, particularly in wafer-scale for practical applications. Here, we report an interfacial proximity-induced high-TC 2D FM Fe3GeTe2 (FGT) via A-type antiferromagnetic material CrSb (CS) which strongly couples to FGT. A superlattice structure of (FGT/CS)n, where n stands for the period of FGT/CS heterostructure, has been successfully produced with sharp interfaces by molecular-beam epitaxy on 2-inch wafers. By performing elemental specific X-ray magnetic circular dichroism (XMCD) measurements, we have unequivocally discovered that TC of 4-layer Fe3GeTe2 can be significantly enhanced from 140 K to 230 K because of the interfacial ferromagnetic coupling. Meanwhile, an inverse proximity effect occurs in the FGT/CS interface, driving the interfacial antiferromagnetic CrSb into a ferrimagnetic state as evidenced by double-switching behavior in hysteresis loops and the XMCD spectra. Density functional theory calculations show that the Fe-Te/Cr-Sb interface is strongly FM coupled and doping of the spin-polarized electrons by the interfacial Cr layer gives rise to the TC enhancement of the Fe3GeTe2 films, in accordance with our XMCD measurements. Strikingly, by introducing rich Fe in a 4-layer FGT/CS superlattice, TC can be further enhanced to near room temperature. Our results provide a feasible approach for enhancing the magnetic order of few-layer 2D FMs in wafer-scale and render opportunities for realizing realistic ultra-thin spintronic devices.  相似文献   

4.
核磁共振永磁体无源匀场的神经网络方法   总被引：1，自引：0，他引：1  
针对核磁共振永磁体的磁场传统匀场方法难度大，经验依赖程度高的情况，提出了人工神经网络应用于磁场匀场的手段。通过基于Matlab的神经网络设计，建立了一个匀场的BP网络模型。由于在磁体的不同的均匀度条件下匀场的方法不同，所以该网络由两个子网络组成----粗调网络和精调网络，并分别对其进行训练。该模型建立之后，可以快速、准确地匀场，使无源匀场不再盲目得进行多次尝试，一次就能使判断准确。通过人工神经网络方法匀场的磁体，均匀度高，满足了核磁共振岩心分析仪的匀场环境。  相似文献   

5.
大体积混凝土温度裂缝的成因与控制   总被引：2，自引：0，他引：2  
众所周知,大体积混凝土内部水化热积聚不易散发,外部则散热较快,很容易由于温度的不均衡分布产生应力,故而产生温度裂缝。本文详细地介绍了大体积混凝土产生裂缝的机理,并从材料、设计、施工方面提出控制手段,引用具体实例进行论证。  相似文献   

6.
Magnetic loss in remanent state ferrites1 has generally been described through the artifice of a magnetic loss tangent (tanδm = μ″?μ′). This characterization is not directly relatable to intrinsic material parameters. The results presented in this paper indicate that magnetic loss in the remanent state can be related to intrinsic material parameters by describing the ferrite mathematically by a complex “average” permeability tensor. The “average” permeability includes the effects of magnetocrystalline anistropy, remanent magnetization, linewidth and an average demagnetizing field appropriate to the distribution of magnetic domains. Experimental examples are given showing that excellent agreement is obtained between theoretically predicted and measured losses.  相似文献   

7.
潘爱民 《大众科技》2012,(5):92-93,61
超导材料是一种具有超导特性的新型材料,它在一定低温条件下能排斥磁力线并且呈现出电阻为零的现象。超导材料由于具有零电阻、完全抗磁性和超导隧道效应等优异的特性,高温超导材料的用途非常广阔,大致可分为三类:大电流应用、电子学应用和抗磁性应用。大电流应用即超导发电、输电和储能;电子学应用包括超导计算机、超导天线、超导器件等;抗磁性主要应用于磁悬浮列车和热核聚变反应堆等。  相似文献   

8.
Room-temperature liquid metal is discovered to be capable of penetrating through macro- and microporous materials by applying a voltage. The liquid metal penetration effects are demonstrated in various porous materials such as tissue paper, thick and fine sponges, fabrics, and meshes. The underlying mechanism is that the high surface tension of liquid metal can be significantly reduced to near-zero due to the voltage-induced oxidation of the liquid metal surface in a solution. It is the extremely low surface tension and gravity that cause the liquid metal to superwet the solid surface, leading to the penetration phenomena. These findings offer new opportunities for novel microfluidic applications and could promote further discovery of more exotic fluid states of liquid metals.  相似文献   

9.
离子液体介质与材料研究进展   总被引：8，自引：0，他引：8       下载免费PDF全文
离子液体介质与材料研究是当前化学化工、功能材料的热点领域之一。1998年底以来,我们以发展离子液体清洁反应介质和软功能材料为研究内容,以实现新离子液体的设计与合成,离子液体中无硫酸Beckmann重排反应、非光气异氰酸酯合成、二氧化碳吸收与活化、反应-升华分离一体化,微孔硅胶限制纳米尺度离子液体材料的设计合成和应用及离子液体-电化学技术集成等为目标开展了一系列研究工作并取得良好进展。  相似文献   

10.
Gamification is increasingly used as an essential part of today’s services, software and systems to engage and motivate users, as well as to spark further behaviors. A core assumption is that gamification should be able to increase the ability of a system or a service to satisfy intrinsic needs, and thereby the autotelicy of use as well as consequent change in beneficial behaviors. However, beyond these optimistic expectations, there is a dearth of empirical evidence on how different gamification features satisfy different dimensions intrinsic needs. Therefore, in this study we investigate the relationships between the user (N = 824) interactions with gamification features (immersion, achievement and social -related features) and intrinsic need satisfaction (autonomy, competence and relatedness needs) in Xiaomi and Huawei online gamified communities that represent two large technology product-related online brand communities in China through a survey-based study. The results indicate that immersion-related gamification features were only positively associated with autonomy need satisfaction. Achievement-related features were not only positively associated with all kinds of need satisfaction, but also the strongest predictor of both autonomy and competence need satisfaction. Social-related gamification features, were positively associated with autonomy, competence and relatedness need satisfaction. The results imply that gamification can have a substantially positive effect on intrinsic need satisfaction for services users.  相似文献   

11.
In this work the applicability of magnetic bubble memories for the processing of inverted files has been discussed. Four novel models of magnetic bubble memories are presented to demonstrate the storage structures and the data processing. The first model employs an organization of major-minor loops. On the basis of such organization a uniform ladder is formed so that the data can be rearranged by using four operations (global shift, detached shift, exchange and delta exchange). The second model makes use of the on-chip decoder (also known as self-contained magnetic bubble-domain memory chip). For this model a hashing scheme is relied upon to perform the required data operations. The third and fourth models are different combinations of the first two models. The latter two models may provide a relatively high-speed performance as well as a reasonable system complexity.For each model the algorithms of data retrieval, sorting, deletion, insertion and updating are given. Also, a comparison of the four models has been carried out in order to determine the most convenient magnetic bubble memory structure for the processing of inverted files.  相似文献   

12.
Energy harvesting devices that prosper in harsh environments are highly demanded in a wide range of applications ranging from wearable and biomedical devices to self-powered and intelligent systems. Particularly, over the past several years, the innovation of triboelectric nanogenerators (TENGs) that efficiently convert ambient kinetic energy of water droplets or wave power to electricity has received growing attention. One of the main bottlenecks for the practical implications of such devices originates from the fast degradation of the physiochemical properties of interfacial materials under harsh environments. To overcome these challenges, here we report the design of a novel slippery lubricant-impregnated porous surface (SLIPS) based TENG, referred to as SLIPS-TENG, which exhibits many distinctive advantages over conventional design including optical transparency, configurability, self-cleaning, flexibility, and power generation stability, in a wide range of working environments. Unexpectedly, the slippery and configurable lubricant layer not only serves as a unique substrate for liquid/droplet transport and optical transmission, but also for efficient charge transfer. Moreover, we show that there exists a critical thickness in the liquid layer, below which the triboelectric effect is almost identical to that without the presence of such a liquid film. Such an intriguing charge transparency behavior is reminiscent of the wetting transparency and van der Waals potential transparency of graphene previously reported, though the fundamental mechanism remains to be elucidated. We envision that the marriage of these two seemingly totally different arenas (SLIPS and TENG) provides a paradigm shift in the design of robust and versatile energy devices that can be used as a clean and longer-lifetime alternative in various working environments.  相似文献   

13.
In cooperation with engineers from Shandong Huate Magnet Technology Co.,Ltd, scientists and technicians from the CAS Institute of High Energy Physics (IHEP) have developed China's first  相似文献   

14.
Defects exist ubiquitously in crystal materials, and usually exhibit a very different nature from the bulk matrix. Hence, their presence can have significant impacts on the properties of devices. Although it is well accepted that the properties of defects are determined by their unique atomic environments, the precise knowledge of such relationships is far from clear for most oxides because of the complexity of defects and difficulties in characterization. Here, we fabricate a 36.8° SrRuO3 grain boundary of which the transport measurements show a spin-valve magnetoresistance. We identify its atomic arrangement, including oxygen, using scanning transmission electron microscopy and spectroscopy. Based on the as-obtained atomic structure, the density functional theory calculations suggest that the spin-valve magnetoresistance occurs because of dramatically reduced magnetic moments at the boundary. The ability to manipulate magnetic properties at the nanometer scale via defect control allows new strategies to design magnetic/electronic devices with low-dimensional magnetic order.  相似文献   

15.
This study describes the development and testing of a magnetic microfluidic chip (MMC) for trapping and isolating cells tagged with superparamagnetic beads (SPBs) in a microfluidic environment for selective treatment and analysis. The trapping and isolation are done in two separate steps; first, the trapping of the tagged cells in a main channel is achieved by soft ferromagnetic disks and second, the transportation of the cells into side chambers for isolation is executed by tapered conductive paths made of Gold (Au). Numerical simulations were performed to analyze the magnetic flux and force distributions of the disks and conducting paths, for trapping and transporting SPBs. The MMC was fabricated using standard microfabrication processes. Experiments were performed with E. coli (K12 strand) tagged with 2.8 μm SPBs. The results showed that E. coli can be separated from a sample solution by trapping them at the disk sites, and then isolated into chambers by transporting them along the tapered conducting paths. Once the E. coli was trapped inside the side chambers, two selective treatments were performed. In one chamber, a solution with minimal nutrition content was added and, in another chamber, a solution with essential nutrition was added. The results showed that the growth of bacteria cultured in the second chamber containing nutrient was significantly higher, demonstrating that the E. coli was not affected by the magnetically driven transportation and the feasibility of performing different treatments on selectively isolated cells on a single microfluidic platform.  相似文献   

16.
Knowledge of intrinsic wettability at solid/liquid interfaces at the molecular level perspective is significant in understanding crucial progress in some fields, such as electrochemistry, molecular biology and earth science. It is generally believed that surface wettability is determined by the surface chemical component and surface topography. However, when taking molecular structures and interactions into consideration, many intriguing phenomena would enrich or even redress our understanding of surface wettability. From the perspective of interfacial water molecule structures, here, we discovered that the intrinsic wettability of crystal metal oxide is not only dependent on the chemical components but also critically dependent on the crystal faces. For example, the crystal face of α-Al2O3 is intrinsically hydrophobic with a water contact angle near 90°, while another three crystal faces are intrinsically hydrophilic with water contact angles <65°. Based on surface energy analysis, it is found that the total surface energy, polar component and Lewis base portion of the hydrophobic crystal face are all smaller than the other three hydrophilic crystal faces indicating that they have different surface states. DFT simulation further revealed that the adsorbed interfacial water molecules on each crystal face hold various orientations. Herein, the third crucial factor for surface wettability from the perspective of the molecular level is presented, that is the orientations of adsorbed interfacial water molecules apart from the macro-level chemical component and surface topography. This study may serve as a source of inspiration for improving wetting theoretical models and designing controllable wettability at the molecular/atomic level.  相似文献   

17.
李容 《科研管理》2013,34(11):114-123
在学术水平不可验证的背景下,以科研成果的数量作为主要绩效依据的职称晋升能否有效分离不同学术水平的科学家并促进学术创新是学术评价制度有效性的一个重要体现。本文基于信息不对称理论的研究框架分析了科研成果的不可验证特征对职称晋升的影响。在此基础上,本文以1338名公共农业科研机构科学家为样本并利用信号理论和probit模型对职称晋升中科研成果的数量能否区分学术水平和学术创新努力不同的科学家进行了证实。理论分析与计量经济学研究结果表明:不可验证性使科研成果的学术水平不适合作为职称晋升的依据;在我国现行职称晋升制度下,科研成果的数量主要是科学家能否晋升职称的信号而非甄别其学术水平和学术创新性的有效方式。  相似文献   

18.
The present paper deals with the transient electromechanical interaction in a thin layer of liquid metal on sudden disruption of an imposed magnetic field. The problem is of fundamental importance for understanding the transient performance of various magnetohydrodynamic devices, such as electromagnetic agitators, pumps, liquid metal machines, etc.  相似文献   

19.
A numerical modeling of natural convection under the influence of either axial (Bz) or radial (Br) magnetic field in a cylindrical configuration filled with a low-Prandtl number electrically conducting fluid, is studied. The finite volume method is used to discretize the equations of continuity, Navier Stokes and energy. A computer program based on the SIMPLER algorithm is developed. The flow and temperature fields are presented by stream function and isotherms, respectively. Stability diagrams are established according to the numerical results of this investigation. These diagrams put in evidence the dependence of the critical Grashof number, Grcr with the increase of the Hartmann number, Ha. The strongest stabilization of the convective flows occurs when the magnetic field is applied in the radial direction. This study confirms the possibility of stabilization of a liquid metal flow in natural convection by application of a radial magnetic field.  相似文献   

20.
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