Investigating the co-substitution impact of yttrium–nickel cations on lattice,morphological and magnetic parameters of SrM based ceramics

This study details the impact of the co-substitution of Y³⁺-Ni³⁺ ions for the Fe³⁺ ions on the structural, morphological and, magnetic parameters of SrM based SrY_xFe_12-2xNi_xO₁₉ (0.00 ≤ x ≥ 0.25) (SrYFeNiO) ceramic magnets synthesized by the ceramic route. Rietveld refinement of XRD confirmed the hexagonal (P63/mmc (194), z = 2) SrFe₁₂O₁₉ phase for all and an additional rhombohedral (R-3c (167), z = 6) hematite Fe₂O₃ phase for x = 0.2, x = 0.25 doping levels. The experimental and theoretical measurements abstracted the stretch of lattice parameters, i.e., the crystallographic axis and the lattice cell volume, and the dislocation of the crystallographic plane (1 1 4) for the hexagonal system, certified the heavy Y³⁺-Ni³⁺ ions substitution. To examine the morphological parameters, FESEM presented the regular hexagonal platelets of sizes ~ 1–2 μm, and EDX revealed the presence of constituent elements with their atomic and weight percentages in SrFeYNiO products. The extraction of vibrational frequencies of Fe–O bonds at tetrahedral and octahedral sites of iron through FT-IR spectroscopy authenticates the formation of the SrM phase. XPS correlated the doped elements, i.e., nickel in Ni⁺² and Ni⁺³ and yttrium in Y⁺³, whereas parent element, i.e., iron in Fe⁺³ and Fe⁺² chemical states, enlightened their impact on the magnetic parameters. Hysteresis loop analysis deduced a linear decline in magnetic parameters such as saturation magnetization (M_s) and remnant magnetization (M_r) due to non-magnetic Y³⁺ and less magnetic Ni³⁺ ions installment in 4f1 and 2b polyhedral sites of Fe³⁺ ions. However, high coercivity (H_c) up to 2.92 kOe ∈ x = 0.15 and extended magnetocrystalline anisotropy (MCA) up to 5.790× 10⁶ Erg/g ∈ x = 0.15 of our obtained ceramic magnets affirmed their application in permanent magnetic industry. M(T) curves also demonstrated the decrease in M_s and displayed an SPM at T_B, which is shifting towards lower temperatures with increasing Y³⁺-Ni³⁺ contents approved the expansion of lattice parameters.     

An Artificial Skyrmion Platform with Robust Tunability in Synthetic Antiferromagnetic Multilayers

Magnetic skyrmions are topologically nontrivial spin structures, and their existence in ferromagnetically coupled multilayers has been widely reported with a disordered arrangement. Here, a nucleation scenario of ordered skyrmions in nanostructured synthetic antiferromagnetic (SAF) multilayers is proposed and experimentally demonstrated using direct magnetization imaging, indirect magnetometer and magnetoresistance measurement, and micromagnetic simulation. Instead of relying on Dzyaloshinskii–Moriya interaction, the antiferromagnetic interlayer exchange coupling in the SAF multilayers fulfills the role of nucleation and stabilization of skyrmions. The robustness of the proposed skyrmion nucleation scenario is examined against temperature from 4.5 to 300 K and device size from 400 to 1200 nm. Interestingly, these synthetic skyrmions still behave well with a size less than 100 nm. The higher stability than generic magnetic domains can be attributed to topological protection. The results thus provide an artificial skyrmion platform to meet the functional needs of high density and designable arrangement in magnonic and spintronic applications.     

磁化曲线的连续可导拟合方法

为了满足磁场储能迭代计算的需要,提出了磁化曲线的连续可导拟合方法。磁化曲线具有高度非线性,难以用一个函数来逼近,根据其特点,提出了线性插值和二次插值相结合的方法,分为三段来拟合。根据曲线连接点处的约束关系,通过求解约束方程获得拟合函数的待定系数,保证了整条曲线的连续可导。由拟合结果给出了磁导率随磁通密度的函数关系及其导函数关系。最后给出了一个具体的拟合算法实例,验证了拟合精度。     

Effects of Indium Doping on the Properties of Cd1-xMnxTe Crystals

通过近红外和红外透过谱表征,确定出掺铟后碲锰镉晶体透过率迅速下降,这是晶格吸收和自由载流子吸收共同作用的结果;而光致发光谱的分析结果表明,掺杂后施主-受主对峰增加,受主束缚激子峰减弱,且随着In含量的增加,受主束缚激子峰消失,只剩下施主-受主对峰。这一系列变化是因为替代的In原子作为施主补偿了Cd空位的缘故。拉曼光谱的测量显示,In掺杂导致"类CdTe"的纵向光学声子峰减弱;而磁学的测试结果则说明In的引入几乎不引起碲锰镉晶体磁化强度的变化。     

Influence of Growth Conditions on Magnetite Nanoparticles Electro-Crystallized in the Presence of Organic Molecules

Magnetite nanoparticles were synthesized by electrocrystallization in the presence of thiourea or sodium butanoate as an organic stabilizer. The synthesis was performed in a thermostatic electrochemical cell containing two iron electrodes with an aqueous solution of sodium sulfate as electrolyte. The effects of organic concentration, applied potential and growth temperature on particle size, morphology, structure and magnetic properties were investigated. The magnetite nanoparticles were characterized by X-ray diffraction, electron microscopy, magnetometry and Mössbauer spectrometry. When the synthesis is performed in the presence of sodium butanoate at 60 °C, a paramagnetic ferric salt is obtained as a second phase; it is possible to avoid formation of this phase, increase the specific magnetization and improve the structure of the oxide particles by tuning the growth conditions. Room-temperature magnetization values range from 45 to 90 Am²kg⁻¹, depending on the particle size, type of surfactant and synthesis conditions. Mössbauer spectra, which were recorded at 290 K for all the samples, are typical of nonstoichiometric Fe_3−δO₄, with a small excess of Fe³⁺, 0.05 ≤ δ ≤ 0.15.     

双筒永磁向心轴承磁力工程化解析算法研究

针对径向磁化的双筒永磁轴承存在磁力计算复杂、由等效磁荷法得出的磁力数学模型不便推广到多筒永磁轴承及缺乏具有明确参量关系的工程化解析磁力计算公式等问题，该文用标量磁位的拉普拉氏方程经复变函数的保角变换等方法，得出一个简明的工程化磁力解析计算公式。该式能明确反映出磁力与相关参量的关系，也便于推广到多筒永磁轴承磁力计算。该式表明：径向磁化的双筒永磁轴承径向磁力分别与磁筒轴向有效长度、剩磁感应强度和永磁圆筒平均半径处磁通密度成正比，磁力随内外磁筒间隙的增大而减小，随间隙半径和径向偏心的增大而增大。实验证明，该模型计算值与实测值基本接近。这为设计径向磁化的双筒永磁轴承和具有更大承载力的多筒永磁轴承提供了一个实用的工具。     

六态矢量Potts模型的相结构和相变性质

本文用变分累积展开（ＶＣＥ）方法对六态矢量Ｐｏｔｔｓ模型的相结构和相变性质进行了研究。在引进单变分参数情况下，系统的自由能，内能，比热和自发磁化强度被计算到四阶近似；在双变分参数情况下，上述物理量被计算到二阶近似。结果表明，系统存在三相结构，在较低温度下发生的是连续相变，而在较高温度下发生的是一级相变。得出的相变位置和用蒙特卡罗（ＭＣ）数值模拟方法给出的结果相一致，体现了用ＶＣＥ方法处理Ｐｏｔｔｓ模型的有效性。比用ＭＣ方法的优越性在于，用ＶＣＥ方法能体现出序参量和内能在一级相变时发生突变的情况。     

不同水岩作用下砂岩的力学参数演化特征

针对水电站边坡岩体在库水浸泡、水位涨落或降雨作用下容易发生滑坡灾害的现象,选取某水电站边坡砂岩为研究对象,研究饱水和干湿循环作用对其力学特性的影响规律,提出了通过比较天然状态、饱水作用以及干湿循环下岩石试样的强度和变形参数的方法.结果表明,随着水岩作用次数的增加,砂岩单轴抗压强度和弹性模量不断减小并趋于恒定,其两者与水岩作用次数呈对数关系,经过干湿循环的试块抗压强度和弹性模量小于经过饱水作用试块.     

JCCl-66型与JCC5-66型电压互感器励磁特性的比较

比较分析了JCCl-66型和JCC5-66型电压互感器的励磁特性。结果表明,JCC5-66型的励磁特性明显优于JCCl-66型。研究表明:提高工艺水平、保证铁心的叠片质量,是避免空载电流偏高的有效措施。     

汽车发动机冷却风扇电动机的研制

给出所研制的钕铁硼永磁汽车冷却风扇电动机的结构、热稳定性、设计原则和试验结果,并对此进行了分析、总结。