Nd substitution in y/ba sites in melt processed YBa2Cu3O7− δ through Nd2O3 additions

YBa₂Cu₃O_{7− δ} (Y123) samples with excess Nd₂O₃ and Y₂O₃ additions in the same molar ratios were melt textured in air. In the Nd-doped samples, in addition to Y ion site substitution, partial substitution into the Ba²⁺ sites is anticipated because of the similar ionic sizes of Nd³⁺ and Ba²⁺. The microstructure, T_c, and magnetic properties of Nd-doped samples were analyzed and compared with undoped Y123 and samples with excess Y₂O₃. The Nd₂O₃ additions lead to significant magnetization improvements, likely due to both rare earth- and Ba-site substitution by the doped Nd³⁺ ions, and to increases in T_c. Y₂O₃ additions resulted in no marked property enhancement.     

Critical state magnetization of hard type-II superconductors with rectangular and cylindrical cross-sections

Magnetization loops in the critical state for the critical current density and are calculated. The geometry considered is an infinitely long superconductor with a finite cross-section in the shape of a rectangle or circle. Explicit formulas are derived for the various branches of the complete high-field hysteresis loop. In the discussion emphasis is put on the behavior of the width, δM, of the hysteresis loop, and a simple graphical method to fit model parameters to experimental data is outlined.     

Impact of the transition metal ion-doped on the electrical and magnetic properties of La0.67Ca0.33MnO3Ag0.15-based polycrystalline ceramics

In this work, high-quality La_0.67Ca_0.33MnO₃:Ag_0.15 and La_0.67Ca_0.33Mn_0.98B_0.02O₃:Ag_0.15 (B = Fe, Co, Ni) ceramics were prepared by the sol–gel route. The slight substitution of the Mn sites has significantly affected the metal–insulator transition and the ferromagnetic–paramagnetic transition. The Mn site doping leads also to a decrease in the temperature of the metal–insulator transition, an enhancement in resistivity, and a reduction in the saturation magnetization. More specifically, the Fe doping approach can significantly increase the peak temperature coefficient of resistance (TCR_peak), since the TCR_peak increases from 62.5%·K^?1 to 75.4%·K^?1. In addition, Fe, Co, and Ni doping can effectively elevate the peak magnetoresistance (MR_peak), of which the modification induced by Fe is the most significant since it enhances from 71.5% to 87.0%. Both the TCR_peak and MR_peak obtained are the highest in the current study, which can greatly promote the application of the manganate materials in the field of infrared detection and magnetic sensitivity.     

磁弹耦合扭转波位移传感器输出电压理论研究

磁弹耦合位移传感器感应线圈电压是由应力波引起的磁化强度变化决定的,而应力与偏置磁铁处的材料磁导率密切相关,因此磁导率与磁化强度变化率的确定是建立输出电压模型的关键.根据铁磁材料的弹性力学理论和磁机耦合模型,确定了扭转波运动方程;建立材料等效场分布模型,并结合麦克斯韦方程和磁化强度进动方程,确定波导丝磁导率;根据磁机效应的Jiles-Atherton理论,建立了波导丝弹性形变感应磁化强度模型.根据磁导率及磁化强度模型,并借助电磁感应定律构建了感应线圈的输出电压模型.利用实验平台验证了接收线圈匝数和激励脉冲的脉宽、频率对输出电压的影响,为磁弹耦合位移传感器的研究提供了理论依据.     

铝合金轴承在无磁产品车中的应用

提出用铝合金轴承代替铜套的设计思路 ,阐述根据轴承负荷、所用材料力学性能决定轴承尺寸的简单方法。研制结果表明 ,铝合金轴承在无磁产品车中的应用 ,满足了委托方的各项技术要求。     

Magnetic properties of Fe-Co-Mo-Cu-B nanocrystalline ribbons with stressing surfaces

Magnetic properties of Fe-Co-Mo-Cu-B alloy system with Co up to 26 at.% were investigated. After proper thermal treatment, the nanocrystalline grain remains tiny, the density hardly increases, but the room-temperature saturation attains 1.5 T mainly due to a high enough Curie temperature. The generally observed slant hysteresis loops point to ribbon surfaces, which stress the ribbon interior and induce a specific magnetoelastic contribution to hard-ribbon-axis magnetic anisotropy even after vacuum annealing. The effect does not come from cobalt but rather from the lack of silicon. Partial removal of the surfaces resulted in a decrease of the loop tilt.     

Large-scale synthesis of high-content Fe nanotubes/nanorings with high magnetization by H2 reduction process

High-content Fe hollow nanostructures from nanotubes (NTs) to nanorings (NRs) have been successfully fabricated by reduction of α-Fe₂O₃ hollow nanostructures at designated temperature. We investigated the influence of reduction condition on the structure and property of the products. With increasing reduction temperature, α-Fe₂O₃ with rhombohedral phase could be converted to cubic inverse spinel phase Fe₃O₄. Thereafter the phase was converted to the dominant cubic Fe preserving the same morphology. The highest M_s is 126 emu/g and 123 emu/g for 70 nm NRs and NTs reduced at 450 °C, respectively. Our results provide a general strategy of reducing single-crystalline α-Fe₂O₃ hollow nanostructures to get high magnetization which is required for many applications.     

Structure, growth and magnetic property of hard magnetic CoPtP nanowires synthesized by electrochemical deposition

This paper reports the electrochemical synthesis and characterization of one dimensional hard magnetic CoPtP nanowires. Three electrode potentiostatic electrochemical technique was used to deposit nanowires into a nanoporous track-etched polycarbonate membrane with a nominal pore diameter 50 nm and thickness around 6-9 μm. The room temperature electrolyte used for the deposition of nanowires consists of 60 g/lt CoSO₄7H₂O, 4.1 g/lt H₂PtCl₆, 4.5 g/lt NaHPO₂ and 25 g/lt B(OH)₃. The structural morphology was observed by scanning electron microscope and transmission electron microscope. The magnetic property of the nanowires was measured by vibrating sample magnetometer before removing the template. The coercive fields were measured to be 143 kA m^− 1 and 103 kA m^− 1 for parallel (H_║) and perpendicular to the nanowire axis, respectively. The higher coercivity value for H_║ indicating nanowires' easy magnetization direction lies along the nanowires' axis. The average composition of the CoPtP nanowires was determined by electron dispersive spectroscopy and the crystallinity was measured by X-ray diffractometer.     

Effect of annealing on the microstructure of NiFe1.925Dy0.075O4 thin films

Dysprosium-doped nickel-ferrite (NiFe_1.925Dy_0.075O₄) thin films were fabricated using RF sputter-deposition. Structural studies indicate that the effect of post-deposition annealing is significant on structural evolution in NiFe_1.925Dy_0.075O₄ films. As-grown NiFe_1.925Dy_0.075O₄ films were amorphous. Annealing (T_a) in air at 450-1000 °C results in the formation of nanocrystalline NiFe_1.925Dy_0.075O₄ films, which crystallize in the inverse spinel structure. The average grain size (L) increases from 5 to 40 nm with increasing T_a from 450 to 1000 °C. Lattice constant of NiFe_1.925Dy_0.075O₄ films is higher compared to that of NiFe₂O₄ due to partial substitution of Dy³⁺ ions for Fe³⁺ ions. The lattice parameter increases from 8.353 to 8.362 Å with increasing T_a from 450 to 1000 °C which is attributed to the lattice-strain developed in the NiFe_1.925Dy_0.075O₄ films with increasing T_a. The corresponding density of NiFe_1.925Dy_0.075O₄ films increases from 3.2 to 3.9 g/cm³ with increasing annealing temperature. Magnetization measurements indicate the ferromagnetic behavior of all the films while the coercive field values at 300 K are found to be 0.0134 T and 0.0162 T for as grown and T_a = 1000 °C films, respectively.     

Influence of Annealing Conditions on Nanocrystalline and Ultra-Soft Magnetic Properties of Fe75.5Cu1Nb1Si13.5B9 Alloy

The magnetic and structural properties of FINEMET alloy with a composition of Fe75.5Cu1Nb1Si13.5B9 were investigated after primary and secondary crystallization of amorphous ribbon sample.The crystallization behavior and the nanocrystal formation of the samples were performed by differential thermal analysis(DTA) which in turn was supported by X-ray diffraction(XRD) study.Temperature dependence of initial permeability of amorphous and devitrified toroid shaped samples has been measured.Enhancement of Curie temperature of the amorphous alloy has been observed due to the irreversible structural relaxation.With the appearance of nanocrystalline phase the Curie temperature of the residual amorphous phase gradually decrease with the increase of annealing temperature.Their temperature dependence reflects the characteristic annealing temperature evolution of the basic magnetic parameters in these nanocrystalline systems.Saturation magnetization,Ms,increases with annealing temperature Ta for the samples and finally decreases during annealing at a temperature much higher than peak crystallization temperature.