Room temperature quantum anomalous Hall insulator in honeycomb lattice, RuCS_(3), with large magnetic anisotropy energy

The quantum anomalous Hall(QAH) effect has attracted enormous attention since it can induce topologically protected conducting edge states in an intrinsic insulating material. For practical quantum applications, the main obstacle is the non-existent room temperature QAH systems, especially with both large topological band gap and robust ferromagnetic order. Here, according to first-principles calculations, we predict the realization of the room temperature QAH effect in a two-dimensional(2D) honeycomb lattice, RuCS_(3) with a non-zero Chern number of C = 1. Especially, the nontrivial topology band gap reaches up to 336 me V for RuCS_(3). Moreover, we find that RuCS_(3) has a large magnetic anisotropy energy(2.065 me V) and high Curie temperature(696 K). We further find that the non-trivial topological properties are robust against the biaxial strain. The robust topological and magnetic properties make RuCS_(3) have great applications in room temperature spintronics and nanoelectronics.

Effect of seed layers on the static and dynamic magnetic properties of CoIr films with negative effective magnetocrystalline anisotropy

The c-axis oriented hcp-Co_(81)Ir_(19)magnetic films were prepared on different seed layers(Ni,Cu,Ir,Pt,Au,and No seed).We systematically investigated the impact that surface-free energy and strain energy have on the orientation and defects and/or internal stress of the grains by increasing the lattice mismatch ratio.Moreover,the initial permeability and the natural resonance frequency were discussed in great detail using a comparison between calculated values and experimental values.We found that the almost unchanged 4πM_(s) andμ_(i) are not affected,while the changed H_(c),intrinsic K_(grain),and f_(r) are strongly dependent on the seed layer and seed layer material.Moreover,the extracted damping constant is sensitive to the defects and/or internal stress and orientation of the grains.Therefore,the soft magnetic properties and microwave properties are adjusted and optimized by seed layers with different materials.

Negative dependence of surface magnetocrystalline anisotropy energy on film thickness in Co_(33)Fe_(67) alloy

In this work, the magnetocrystalline anisotropy energy(MAE) on the surface of FeCoalloy film is extracted from x-ray magnetic linear dichroism(XMLD) experiments. The result indicates that the surface MAE value is negatively correlated with thickness. Through spectrum calculations and analysis, we find that besides the thickness effect, another principal possible cause may be the shape anisotropy resulting from the presence of interface roughness. These two factors lead to different electron structures on the fermi surface with different exchange fields, which produces different spin–orbit interaction anisotropies.

Magnetic tuning in a novel half-metallic Ir_(2)TeI_(2) monolayer

A two-dimensional(2D) high-temperature ferromagnetic half-metal whose magnetic and electronic properties can be flexibly tuned is required for the application of new spintronics devices. In this paper, we predict a stable Ir_(2)TeI_(2) monolayer with half-metallicity by systematical first-principles calculations. Its ground state is found to exhibit inherent ferromagnetism and strong out-of-plane magnetic anisotropy of up to 1.024 meV per unit cell. The Curie temperature is estimated to be 293 K based on Monte Carlo simulation. Interestingly, a switch of magnetic axis between in-plane and out-of-plane is achievable under hole and electron doping, which allows for the effective control of spin injection/detection in such 2D systems. Furthermore, the employment of biaxial strain can realize the transition between ferromagnetic and antiferromagnetic states. These findings not only broaden the scope of 2D half-metal materials but they also provide an ideal platform for future applications of multifunctional spintronic devices.

基于磁各向异性的管壁应力集中区域检测方法

针对应力集中导致管壁发生屈服失效的问题,提出了利用磁各向异性检测管壁应力集中区域的方法。从能量角度出发,研究了应力导致管壁产生磁各向异性的机理,建立了管壁当量应力与磁各向异性探头输出电压信号的数学模型,通过计算管壁的当量应力判断其是否发生屈服失效,搭建了应力检测实验平台。实验结果表明,应力会导致管壁产生磁各向异性,磁各向异性检测方法能够检测出管壁当量应力的变化趋势和主应力方向所在延长线的角度,进而判断管壁是否产生应力集中区域。

考虑磁畴偏转的无取向硅钢应力各向异性磁致伸缩特性模拟

无取向硅钢铁心的电磁振动是电机噪声的根本来源,采用夹件固定铁心可有效抑制其振动,但夹紧力施加不当会加剧铁心振动,原因为应力使无取向硅钢的磁畴取向发生偏转而引起磁致伸缩形变增大,形成应力各向异性。因此,为了获得准确的应力加载方法,需建立考虑磁畴偏转的无取向硅钢应力各向异性磁致伸缩模型。首先,求解自由能模型并计算能量极值点的分布,模拟无取向硅钢在磁场和应力作用下的磁畴偏转路径;其次,用磁晶各向异性能、应力各向异性能以及磁场能贡献的总和表示无磁滞磁化强度,将自由能模型与考虑磁滞的磁致伸缩模型相结合,通过无取向硅钢磁致伸缩特性测试获取模型参数并进行参数依赖性分析;最后,模拟应力与磁场作用下不同磁化方向的无取向硅钢的磁滞特性和磁致伸缩特性,通过仿真结果与实验结果的对比验证了该模型的准确性。结果表明,应力的增大会使无取向硅钢磁致伸缩应变值减小,同一应力下,磁致伸缩应变的大小会随磁化角度的增大而增大,该文所提出的应力各向异性磁致伸缩模型可以有效模拟此种变化规律。

Controllable high Curie temperature through 5d transition metal atom doping in CrI_(3)

Two-dimensional(2D) CrI_(3) is a ferromagnetic semiconductor with potential for applications in spintronics. However,its low Curie temperature(T_(c)) hinders realistic applications of CrI3. Based on first-principles calculations, 5d transition metal(TM) atom doping of CrI_(3)(TM@CrI_(3)) is a universally effective way to increase T_(c), which stems from the increased magnetic moment induced by doping with TM atoms. T_(c) of W@CrI_(3) reaches 254 K, nearly six times higher than that of the host CrI_(3). When the doping concentration of W atoms is increased to above 5.9%, W@CrI_(3) shows room-temperature ferromagnetism. Intriguingly, the large magnetic anisotropy energy of W@CrI_(3) can stabilize the long-range ferromagnetic order. Moreover, TM@CrI_(3) has a strong ferromagnetic stability. All TM@CrI_(3) change from a semiconductor to a halfmetal, except doping with Au atom. These results provide information relevant to potential applications of CrI_(3) monolayers in spintronics.

Electronic property and topological phase transition in a graphene/CoBr_(2) heterostructure

Recently,significant experimental advancements in achieving topological phases have been reported in van der Waals(vdW)heterostructures involving graphene.Here,using first-principles calculations,we investigate graphene/CoBr_(2)(Gr/CoBr_(2))heterostructures and find that an enhancement of in-plane magnetic anisotropy(IMA)energy in monolayer CoBr_(2) can be accomplished by reducing the interlayer distance of the vdW heterostructures.In addition,we clarify that the enhancement of IMA energy primarily results from two factors:one is the weakness of the Co-d_(xy) and Co-d_(x^(2)-y^(2)) orbital hybridization and the other is the augmentation of the Co-d_(yz) and Co-d_(z)2 orbital hybridization.Meanwhile,calculation results suggest that the Kosterlitz–Thouless phase transition temperature(TKT)of a 2D XY magnet Gr/CoBr_(2)(23.8 K)is higher than that of a 2D XY monolayer CoBr_(2)(1.35 K).By decreasing the interlayer distances,the proximity effect is more pronounced and band splitting appears.Moreover,by taking into account spin–orbit coupling,a band gap of approximately 14.3 meV and the quantum anomalous Hall effect(QAHE)are attained by decreasing the interlayer distance by 1.0 A.Inspired by the above conclusions,we design a topological field transistor device model.Our results support that the vdW interlayer distance can be used to modulate the IMA energy and QAHE of materials,providing a pathway for the development of new low-power spintronic devices.

Perspective and Prospects for Rare Earth Permanent Magnets

Rare earth permanent magnets constitute a mature technology,but the shock of the 2011 rare earth crisis led to the re-evaluation of many ideas from the 1980s and 1990s about possible new hard magnets containing little or no rare earth(or heavy rare earth).Nd-Fe-B magnets have been painstakingly and skillfully optimized for a wide range of applications in which high performance is required at reasonable cost.Sm-Co is the material of choice when high-temperature stability is required,and Sm-Fe-N magnets are making their way into some niche applications.The scope for improvement in these basic materials by substitution has been rather thoroughly explored,and the effects of processing techniques on the microstructure and hysteresis are largely understood.A big idea from a generation ago-which held real potential to raise the record energy product significantly-was the oriented exchange-spring hard/soft nanocomposite magnet;however,it has proved very difficult to realize.Nevertheless,the field has evolved,and innovation has flourished in other areas.For example,electrical personal transport has progressed from millions of electric bicycles to the point where cars and trucks with electrical drives are becoming mainstream,and looks ready to bring the dominance of the internal combustion engine to an end.As the limitations of particular permanent magnets become clearer,ingenuity and imagination are being used to design around them,and to exploit the available mix of rare earth resources most efficiently.Huge new markets in robotics beckon,and the opportunities offered by additive manufacturing are just beginning to be explored.New methods of increasing magnet stability at elevated temperature are being developed,and integrated multifunctionality of hard magnets with other useful properties is now envisaged.These themes are elaborated here,with various examples.

ENERGY STORAGE IN METAL DEVICES AND THE ADVANTAGES OF LIQUID HYDROGENTEMPERATURES

Peculiarities of low temperature charge transport and enerpy accumulation in alu-minum devices are investigated by means of study of cylindrical conductors having a rudial cuerent fiow between inner and outer concentric contracts. Azimuthal current and, connected with it, self magnetic field are investigated in a wide range of radial current density up to 6000 A/cm2 under an external magnetic field up to 8 T Electron scattering processes are investigated and it is shown that relaxation electron mechanisms are determined by strong temperature dependence on account of high sus-ceptibility of scattering to anisotropy of electron dispersion law. The role of thermal phonons is investigated through an effective averaged conductivity tensor of polycrystalline medium. Using data of self magnetic self distribution on sample surface an energy density of self magnetic field is estimated. It is shown that at T=4.2 K average energy of self field may achieve at least 1 J/cm3. Using data of relaxation processes at temperature of liquid hydrogen it is established that self magnetic field must be a third of helium magnitude with respective self magnetic enengy density, spiral motion of carriers in this geometry being regarded as a current coils in usual inductive element.

Janus monolayer TaNF:A new ferrovalley material with large valley splitting and tunable magnetic properties

Materials with large intrinsic valley splitting and high Curie temperature are a huge advantage for studying valleytronics and practical applications.In this work,using first-principles calculations,a new Janus TaNF monolayer is predicted to exhibit excellent piezoelectric properties and intrinsic valley splitting,resulting from the spontaneous spin polarization,the spatial inversion symmetry breaking and strong spin-orbit coupling(SOC).TaNF is also a potential two-dimensional(2D)magnetic material due to its high Curie temperature and large magnetic anisotropy energy.The effective control of the band gap of TaNF can be achieved by biaxial strain,which can transform TaNF monolayer from semiconductor to semi-metal.The magnitude of valley splitting at the CBM can be effectively tuned by biaxial strain due to the changes of orbital composition at the valleys.The magnetic anisotropy energy(MAE)can be manipulated by changing the energy and occupation(unoccupation)states of d orbital compositions through biaxial strain.In addition,Curie temperature reaches 373 K under only−3%biaxial strain,indicating that Janus TaNF monolayer can be used at high temperatures for spintronic and valleytronic devices.

稀土原子Gd沉积在石墨烯衬底上的电子结构和磁性研究

当前磁性纳米结构具有高的磁性稳定性和大的磁各向异性能(MAE),在自旋电子器件中具有巨大的应用潜力。采用基于密度泛函理论(DFT)之外的DFT+U方法,系统研究了Gd原子相对于石墨烯放置在不同位置吸附构型的结构稳定性、电子结构和磁性。结果表明,Gd吸附在石墨烯空位时是能量最低的构型。体系中Gd原子的自旋磁矩主要是由其f轨道的电子贡献,磁各向异性能主要来源于Fermi面附近d轨道的电子跃迁。在电子结构分析的基础上,我们提出了Gd-d轨道和C原子发生杂化决定了结构的稳定性。该体系优异的磁稳定性和大磁矩使其成为自旋电子应用方面极具前途的候选材料。

双取向硅钢不同方向磁性的研究

研究了一种双取向硅钢不同方向的磁感(B8)及其与织构和磁晶各向异性能(EK)之间的关系。结果表明:该双取向硅钢的织构主要为{100}〈001〉,其磁感随方向的变化而发生有规律的变化,这种变化规律与铁单晶体中不同晶轴方向的磁晶各向异性能的变化规律一致。

L1_0有序FePt磁记录薄膜研究进展

L10有序FePt合金薄膜具有高磁晶各向异性能、高矫顽力、高磁能积、高居里温度和抗腐蚀能力强等优点,能够满足超高密度磁记录的要求,极有可能成为下一代超高密度磁存储介质。详细介绍了FePt薄膜近年来的研究成果,分析了降低FePt有序化温度,减小FePt颗粒的粒径,减弱晶粒间相互作用和控制其易磁化轴取向的方法,并对其应用前景作了分析。

磁场作用下磁性聚氨酯泡沫的力学和吸声性能分析

使用实验室自主研制的磁场设备,以添加了羰基铁粉的磁性聚氨酯泡沫为对象,研究磁场对磁性泡沫力学性能和低频吸声性能的影响,探寻智能磁性泡沫聚合物吸声性能和力学性能的可调性。首先采用一步全水发泡法,制备了质量分数为80%(质量分数)的各项异性与各向同性的磁性聚氨酯泡沫。接着基于美国TA流变仪,在交变的磁场作用下,测量这两种泡沫储能模量的变化。基于传递函数法,利用双通道阻抗管,测量在不同强度磁场下两种泡沫的吸声性能。实验结果发现,磁场的施加对各向异性与各向同性磁性聚氨酯泡沫的吸声性能影响有限,但其储能模量会随着磁场大小的绝对值增加而逐渐增加,经过时长为500 s,最大周期为0.5 T的交变磁场作用,各向同性聚氨酯泡沫的储能模量上升了14.6%,各项异性的上升了15.8%,这意味着磁场会增加磁性粒子短链之间的应力传递。

Nd^(3+)的稳定能与晶场参数及磁交换作用的关系

基于单离子模型,通过对Nd3+磁晶各向异性哈密顿数值的求解,研究了温度趋于0 K时,Nd3+离子稳定能与晶场参数及磁交换作用的关系.结果表明,对于强磁物质(如NdCo5,Nd2Co17,Nd2Fe14B等),Nd3+贡献的稳定能与晶场参数B20近似成正比,而对磁交换作用的变化不敏感.

表面脉冲电磁场处理下7A04铝合金凝固组织演变

采用一种新型熔体表面脉冲电磁技术对7A04超硬铝合金凝固组织进行细化处理。通过分析脉冲电磁场对组织形貌、晶体择优取向及凝固温度过程的影响,探讨脉冲电磁场下凝固组织演变机理。结果表明,随着脉冲电磁场强度增加,凝固组织发生球化细化→枝晶化再粗化的转变;在磁场强度为241mT时,晶粒尺寸可降低40%左右。由于晶体磁各向异性产生的磁能差导致凝固初期尺寸为225nm^100μm的晶粒发生转动,晶粒择优生长;此外,在脉冲电磁场孕育处理条件下,熔体凝固初期温度升高导致固相分数降低,有利于晶核运动,也可获得良好的组织细化效果。

二维单层CrX3的电子结构及电荷掺杂对磁各向异性能调控的第一性原理研究

用第一性原理计算的方法研究了二维单层CrX3(X=Cl、Br和I)的原子、电子结构和磁性.结果表明二维单层CrX3都是铁磁半导体.还研究了电荷掺杂对CrX3(X=Cl、Br和I)体系磁各项异性能(MAE)的影响.结果表明,电荷掺杂可以极大地调控单层CrBr3和CrI3的MAE,但是对CrCl3的调控不明显.

铁磁性纳米片间相互作用对其微波磁性的影响

在铁磁性元素中,交换能、偶极能和各向异性能之间存在复杂的竞争,因此,这种结构化介质的静态和动态性能与构成材料的固有磁特性,各个元素的形状和尺寸等有着密切的关系.这些多个自由度提供了对于通常未构图的磁性薄膜不可达到的新性能.本文通过将所研究的系统划分成立方体网格的三维阵列来对其进行建模,研究具有不同相对位置、纳米片间距、磁各向异性方向的两矩形铁磁性纳米片的微波磁性能.研究发现:与单个矩形铁磁性纳米片相比,具有不同相对位置、纳米片间距的两矩形铁磁性纳米片共振峰频率分布发生变化;当两矩形纳米片磁各向异性方向所呈角度由0°增加到30°时,其磁性质没有明显变化,而从30°到90°时,其磁性质对磁各向异性方向变化比较敏感.通过调控纳米片的相对位置、纳米片间距以及磁各向异性方向可以制备具有良好性能的吸收材料.

一个新颖的混合配体双核镝(Ⅲ)配合物:合成、结构和磁性能研究

通过溶剂热方法合成了一个以4′-(对苯酚)-2, 2′:6′, 2"-三联吡啶(L1)和N, N'-双(亚水杨基)亚乙二胺(L_2)为混合配体的稀土金属配合物[Dy_2(L_1)_2(L_2)Cl_2(SCN)_4],并通过单晶和粉末X-射线衍射、元素分析、红外光谱、热重分析、直流和交流磁化率对其结构和磁学性能进行了全面地表征。该配合物结晶于三斜P1空间群,晶胞参数为a=0.90268(4) nm,b=0.90572(3) nm,c=1.91170(7) nm,α=83.092(3)o,β=82.848(3)o,g=74.189(4)o,V=1.4860(11) nm^3,Z=1。在该配合物中,中性的N, N'-双(亚水杨基)亚乙二胺配体连接相邻的Dy~Ⅲ离子形成中心对称的松散双核结构,而具有大p共轭骨架的三联吡啶分子则作为封端配体参与Dy~Ⅲ离子配位多面体的构建。更为有趣的是,源于五角双锥构型的Dy~Ⅲ离子的强各向异性,该配合物呈现出场诱导的单分子磁体行为,其磁矩翻转的有效能垒和指前因子分别为42.7 K和1.3×10^(-6) s。